Free radical bimolecular reaction rate constant measuring system and method

Abstract

The invention discloses a free radical bimolecular reaction rate constant measuring system and a free radical bimolecular reaction rate constant measuring method, and relates to the technical field of atmospheric environment measurement. Free radical precursors and / or reactants are introduced into a reaction cavity, and photolysis light beams are used for photolysis of the free radical precursors to generate free radicals; the absorption detection module emits absorption light beams to the reaction cavity, the absorption light beams are absorbed by free radicals and collect absorption light beam signals, and the fluorescence detection module collects the free radicals generated by the reaction module into the fluorescence cavity, emits laser to the fluorescence cavity to excite the free radicals to generate fluorescence signals and collects the fluorescence signals; the free radical concentration change is measured according to the light intensity change of the absorbed light beam, the free radical activity is obtained, the free radical activity is obtained according to the change of the fluorescence signal, and the two modes are mutually verified; measuring free basic substrate activity without reactants and free radical activity under different reactant concentrations, and performing linear fitting to obtain a bimolecular reaction rate constant of the free radicals. The method solves the problem that the error of the free radical bimolecular reaction rate is large.

Description

Technical Field

[0001] The present invention relates to the technical field of atmospheric environment measurement, and in particular to a measurement system and method for the rate constant of free radical bimolecular reactions. Background Art

[0002] Free radicals in the atmosphere rapidly convert primary pollutants into secondary pollutants, determining the level of atmospheric oxidizing ability. However, the reactions of free radicals with some trace gases in the atmosphere are not well understood (such as Criegee radicals), and research has only started in recent years. First, some research groups have realized laboratory measurements of free radical bimolecular reaction kinetics using methods such as vacuum ultraviolet photoionization mass spectrometry, ultraviolet absorption spectroscopy, laser-induced fluorescence, and infrared-visible light. For the measurement of the reaction rate constant of free radicals, including direct measurement, indirect measurement, and theoretical calculation, most of the results between different measurement methods and different measurement systems are inconsistent. Second, the total amount of relevant research on the measurement of the free radical bimolecular reaction rate constant is small, and there are contradictions between some bimolecular reaction results, which need to be further explored. Accurately measuring the bimolecular reaction rate constant of free radicals with atmospheric trace gases is of great research significance for the accurate quantification of atmospheric oxidizing ability. In addition, basic data related to free radicals are lacking, so the measurement of their rate constants can be used to supplement the basic parameters of the model.

[0003] Exploring the kinetics of free radical bimolecular reactions is of scientific significance for improving the research on atmospheric oxidizing ability and the formation mechanism of secondary pollutants. It is necessary to develop a device and method that can directly measure the bimolecular reaction rate constant of free radicals with various primary pollutants in the same system using different detection methods. Summary of the Invention

[0004] In order to overcome the above defects in the prior art, the present invention provides a measurement system and method for the rate constant of free radical bimolecular reactions, specifically involving laboratory measurements of the bimolecular reaction rate constant of free radicals in the atmosphere, and solving the problem of large errors in the rate of free radical bimolecular reactions.

[0005] To achieve the above object, the present invention adopts the following technical solutions, including:

[0006] A measurement system for the rate constant of free radical bimolecular reactions, the system includes: a sampling module, a reaction module, an absorption detection module, a fluorescence detection module, and a collection module;

[0007] The sampling module is connected to the reaction module and is used to introduce free radical precursors and / or reactants into the reaction chamber of the reaction module;

[0008] The reaction module uses a photolysis beam to photolyze free radical precursors in the reaction chamber to generate free radicals;

[0009] The absorption detection module is used to emit an absorption beam into the reaction chamber for radicals to absorb, and collect the signal of the absorption beam after being absorbed by the radicals;

[0010] The fluorescence detection module is used to collect the radicals generated by the reaction module into the fluorescence chamber, emit a laser into the fluorescence chamber to excite the radicals to generate fluorescence signals, and collect the fluorescence signals;

[0011] The acquisition module is used to receive various signals collected in the system and monitor various controllable devices in the system, and calculate the bimolecular reaction rate constant of radicals according to the detected signals.

[0012] Preferably, the sample injection module includes: a bubbler filled with a radical precursor, a blowing gas, a dilution gas, oxygen, and a reaction gas;

[0013] The blowing gas is connected to the bubbler through a second mass flow controller and is used to blow out the radical precursor in the bubbler;

[0014] The dilution gas is combined with the radical precursor blown out of the bubbler through a first mass flow controller and is used to dilute the radical precursor to obtain a first synthesis gas;

[0015] The oxygen passes through a third mass flow controller, and the reaction gas passes through a fourth mass flow controller and is combined with the first synthesis gas to obtain a second synthesis gas;

[0016] The second synthesis gas is introduced into the reaction chamber of the reaction module.

[0017] Preferably, the reaction module includes: a reaction chamber, a first window, a second window, a first light source, beam expansion, a first energy probe, a temperature and humidity probe, a first pressure gauge, and a first air pump;

[0018] The photolysis beam emitted by the first light source is collimated through beam expansion. After expanding the spot diameter, it enters the reaction chamber through the first window at one end of the reaction chamber, photolyzes the radical precursor in the reaction chamber to generate radicals, and then the photolysis beam exits through the second window at the other end of the reaction chamber and is monitored for energy by the first energy probe;

[0019] The temperature and humidity probe and the first pressure gauge are used to collect the temperature, humidity, and pressure in the reaction chamber; the first air pump is used to pump out the gas in the reaction chamber.

[0020] Preferably, the absorption detection module includes a second light source, a first high reflector, a second high reflector, a first detector, and a first timing control module;

[0021] The absorption beam emitted by the second light source passes through the first highly reflective mirror at one end of the reaction chamber and enters the reaction chamber, where it is reflected multiple times between the first highly reflective mirror and the second highly reflective mirror at both ends of the reaction chamber and is absorbed by free radicals at the same time. Subsequently, it passes through the second highly reflective mirror at the other end of the reaction chamber and exits, and the absorption beam signal is collected by the first detector; the first timing control module is used to control the first detector to collect the absorption beam intensity at different times after each emission of the absorption beam.

[0022] Preferably, the fluorescence detection module includes a fluorescence chamber, a third light source, an optical fiber coupling module, a second energy probe, a free radical collection module, a second air pump, a second pressure gauge, a second detector, and a second timing control module;

[0023] The laser emitted by the third light source is collimated by the optical fiber coupling module and then enters the fluorescence chamber; the free radical collection module uses a nozzle to collect the free radicals in the reaction chamber into the fluorescence chamber in a jet manner; the free radicals in the fluorescence chamber are excited by the laser to generate fluorescence signals; the second detector is used to collect the fluorescence signals; the second timing control module is used to control the opening or closing of the second detector; the second air pump is used to pump out the gas in the fluorescence chamber; the second pressure gauge is used to collect the pressure in the fluorescence chamber; the second energy probe is used to monitor the energy of the laser emitted through the fluorescence chamber.

[0024] The present invention also provides a method for measuring the bimolecular reaction rate constant of free radicals, which is applicable to the above-mentioned system for measuring the bimolecular reaction rate constant of free radicals. The method is as follows:

[0025] Step 1: Only introduce the free radical precursor into the reaction chamber. At this time, the measured free radical activity is the reaction activity of the free radicals themselves, that is, the free radical background activity ko;

[0026] Step 2: Introduce the free radical precursor and reactants with different concentrations into the reaction chamber, and measure the free radical activity k at different reactant concentrations, where Y is the reactant concentration;

[0027] Step 3: Perform linear fitting based on the measured free radical background activity ko and the free radical activity k at different reactant concentrations, and the bimolecular reaction rate constant of the free radicals can be obtained. The fitting expression is: k = ko + v×Y; where v is the bimolecular reaction rate constant of the free radicals.

[0028] Preferably, there are two ways to measure the free radical activity:

[0029] First, calculate the free radical concentration according to the absorption beam signal collected by the absorption detection module; and based on the change in the free radical concentration, fit to obtain the free radical activity;

[0030] Second, based on the fluorescence signals collected by the fluorescence detection module and the changes in the fluorescence signals, the radical activity is obtained by fitting.

[0031] Based on the two measurement methods, the measurement results of the radical activity are mutually verified. If the difference in the radical activity obtained by the two measurement methods does not exceed the set threshold, it indicates that the measurement result of the radical activity is reliable, and the test result of one of the measurement methods or the test results of the two measurement methods are weighted and fused; otherwise, it indicates that the measurement result of the radical activity is unreliable.

[0032] Preferably, the first measurement method is as follows:

[0033] Detect the change in the intensity of the absorption beam, and measure the radical concentration in real time according to the Lambert-Beer law. The calculation formula is as follows:

[0034]

[0035] Wherein, X is the radical concentration measured in real time; R L is the effective cavity length, that is, the ratio of the cavity length to the single-pass absorption optical path length of the gas in the cavity; c is the speed of light; σ is the absorption cross-section of the gas to be measured; τ is the decay time when there are radicals in the reaction cavity, and τ 0 is the background decay time when there are no radicals in the reaction cavity;

[0036] Perform exponential fitting on the radical concentration X measured in real time and the time t. The exponential fitting formula is:

[0037]

[0038] Wherein, X t is the radical concentration at time t, and X 0 is the radical concentration at the initial time; k 1 is the radical activity obtained by the first measurement method.

[0039] Preferably, the second measurement method is as follows:

[0040] Perform double-exponential fitting on the fluorescence signal measured in real time and the time t. The double-exponential fitting formula is:

[0041]

[0042] Wherein, S radical is the fluorescence signal measured in real time, and A 0 , A 1 and a are all parameters of the double-exponential fitting; k 2 is the radical activity obtained by the second measurement method.

[0043] The present invention also provides a computer program product, which is characterized in that it includes a computer program / instructions, and when the computer program / instructions are executed by a processor, the method for measuring the rate constant of a radical bimolecular reaction is implemented.

[0044] The advantages of the present invention are as follows:

[0045] (1) The present invention solves the problem of large errors in the rate of radical bimolecular reactions. For the same reaction state of radicals, the rate constants of the bimolecular reactions between radicals and atmospheric pollutants are synchronously measured by different techniques, and the advantages of different measurement techniques are combined to improve the accuracy of measurement.

[0046] (2) The rate constant of the radical bimolecular reaction is measured by combining fluorescence detection and absorption detection. Both of these methods are highly sensitive absolute measurement methods, and the measurement results of the two can be mutually verified, avoiding the interference of overlapping absorption spectra that may be brought about by relying solely on the absorption detection method.

[0047] (3) The free radical background activities measured by the two measurement methods ensure the stability and reliability of the background activity under mutual verification, and ensure the accuracy of the measurement results of the bimolecular reaction rate constant in the subsequent linear fitting.

[0048] (4) In the actual measurement process of the rate constant of the radical bimolecular reaction by combining fluorescence detection and absorption detection, a radical precursor and a reactant participating in the radical bimolecular reaction are introduced into the reaction module, and the activity values at different concentration gradients are obtained by adjusting the concentration of the reactant. A linear fit is performed on the reactant concentrations at different gradients and the apparent reaction activities to obtain the rate constant of the radical bimolecular reaction; on the premise of having obtained an accurate free radical background activity, the accuracy of the bimolecular reaction rate constants obtained by the two methods is also ensured.

[0049] (5) A reaction chamber with a hexagonal cross-section is designed to implement the two measurement methods synchronously, and a scheme of introducing gas in the middle and light on both sides is adopted. First, this ensures the consistency of the measurement of the sampling gas by the two methods while measuring as many sampling gases as possible; second, the light is introduced on both sides through two window plates and two total reflection mirrors. The absorption beam and the photolysis beam cross in the reaction chamber, and the photolysis of the precursor and the simultaneous detection of the radical concentration are completed at the beam crossing point, ensuring the accuracy of the radical concentration measurement.

[0050] (6) The sampling port of the fluorescence detection module is located directly below the intersection of the absorption beam and the photolysis beam. The sampling port is in contact with the intersection of the beams, thus enabling real-time detection of the free radical concentration. Therefore, this design ensures the synchronous realization of precursor dissociation, free radical generation, free radical absorption detection, and free radical fluorescence detection. In addition, the window and the total reflection mirror are equipped with customized pressing plates and pressing rings, which also ensure the airtightness of the reaction module. Good airtightness guarantees the stability of the measurement results.

[0051] (7) Design a timing control module to achieve continuous dual measurement methods, which is realized by using a timing control card and timing design. The absorption detection module controls the opening and closing of the corresponding first detector through the first timing control module. At a certain moment t 0 after the ultraviolet light emission, it is turned on, and at t 0 +△t after the next ultraviolet light emission, it is turned on. After accumulating a certain amount of △t, the decay curve of the free radical concentration changing with time is obtained. After the third light source emits a TTL square wave signal, the second timing control module controls the opening and closing of the corresponding second detector through timing settings, ensuring that as many fluorescence signals as possible are collected while also protecting the detector from laser damage. The second timing control module controls the second detector to perform multiple acquisitions between adjacent laser pulses, and then obtains the fluorescence decay signal generated after the free radicals are excited. Such timing control settings ensure the synchronous continuous detection of the two measurement methods and also achieve the purpose of protecting the detector from laser damage. Description of the Drawings

[0052] Figure 1 It is an overall schematic diagram of a measurement system for the reaction rate constant of a free radical bimolecular reaction.

[0053] Figure 2 It is a schematic diagram of the fluorescence detection module.

[0054] Figure 3 It is a schematic diagram of the reaction module.

[0055] Description of the Reference Numerals:

[0056] 1 - Reaction chamber, 2 - Beam expander, 3 - First light source, 401 - First total reflection mirror, 402 - Second total reflection mirror, 101 - First window, 102 - Second window, 103 - First high reflection mirror, 104 - Second high reflection mirror, 5 - Second light source, 601 - Third total reflection mirror, 602 - Fourth total reflection mirror, 7 - First detector, 8 - First timing control module, 9 - First energy probe, 10 - Third light source, 11 - Fiber optic coupling module, 12 - Conical aperture, 13 - Second energy probe, 14 - Free radical collection module, 15 - Second air pump, 16 - Second pressure gauge, 17 - Second detector, 18 - Second timing control module, 19 - Temperature and humidity probe, 20 - First pressure gauge, 21 - First air pump, 22 - Sampling module, 2301 - First mass flow controller, 2302 - Second mass flow controller, 2303 - Third mass flow controller, 2304 - Fourth mass flow controller, 2401 - Diluent gas, 2402 - Oxygen, 2403 - Reaction gas, 25 - Bubbler, 26 - Industrial control computer. Detailed implementation

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] Embodiment 1

[0059] As Figures 1 - 3 shown, a measurement system for the bimolecular reaction rate constant of free radicals includes a sampling module 22, a reaction module, an absorption detection module, a fluorescence detection module, and a collection module.

[0060] The sampling module 22 is connected to the reaction module and introduces free radical precursors and / or reactants into the reaction chamber 1 of the reaction module.

[0061] The reaction module is used for the generation of free radicals, and photolyzes the free radical precursors in the reaction chamber 1 using a photolysis beam to generate free radicals.

[0062] The absorption detection module emits an absorption beam towards the reaction chamber 1 and is absorbed by the free radicals, and collects the signal of the absorption beam after being absorbed by the free radicals for measuring the free radical concentration at a certain wavelength. The absorption detection module and the reaction module are located within the same mechanical structure.

[0063] The fluorescence detection module is used to collect the free radicals generated by the reaction module into the fluorescence cavity, emit a laser into the fluorescence cavity to excite the free radicals to generate fluorescence signals, and collect the fluorescence signals while monitoring the energy intensity of the emitted laser. The fluorescence detection module is located below the left side of the reaction module and is connected to the reaction module through an adapter mechanical structure and screws.

[0064] The acquisition module is used to receive various signals collected in the system and monitor various controllable devices, and connect the devices in the system to the industrial control computer through various signal connection lines.

[0065] The following is a detailed description of the system structure:

[0066] The sample injection module 22 includes a first mass flow controller 2301, a second mass flow controller 2302, a third mass flow controller 2303, and a fourth mass flow controller 2304, as well as various gases for generating free radicals, including a dilution gas, a blowing gas, oxygen 2402, and a reaction gas (reactant) 2403, and a bubbler 25 containing a free radical precursor (such as diiodomethane CH 2 I 2 ).) In this embodiment, both the dilution gas and the blowing gas are nitrogen 2401.

[0067] Nitrogen 2401, as the blowing gas, passes through the second mass flow controller 2302 and is introduced into the bubbler 25 to blow out the free radical precursor; nitrogen 2401, as the dilution gas, passes through the first mass flow controller 2301 and merges with the free radical precursor blown out by the bubbler 25 to obtain a first synthesis gas, and the concentration of the free radical precursor is adjusted by controlling the flow ratio of the two gases; oxygen passes through the third mass flow controller (2303), and the reaction gas passes through the fourth mass flow controller (2304) and then merges with the first synthesis gas through a tee joint to obtain a second synthesis gas. The second synthesis gas is introduced into the reaction cavity 1 of the reaction module.

[0068] The reaction module includes a reaction cavity 1, a first light source 3, a beam expander 2, a first total reflection mirror 401, a second total reflection mirror 402, a first window 101, a second window 102, a first energy probe 9, a temperature and humidity probe 19, a first pressure gauge 20, and a first air pump 21.

[0069] The reaction chamber 1 is a place for generating free radicals. The reaction chamber 1 is a cavity structure with a hexagonal cross-section, with gas inlet in the middle and light inlets on both sides. The photolysis beam emitted by the first light source 3 enters the beam expander 2 after passing through the first total reflection mirror 401 and the first total reflection mirror 402. After being collimated by the beam expander 2 and expanding the beam spot diameter, it enters the reaction chamber 1 through the first window 101 at one end of the reaction chamber 1. The photolysis beam with an expanded spot diameter can more fully photolyze the free radical precursor to generate sufficient free radicals. Subsequently, the photolysis beam exits through the second window 102 at the other end of the reaction chamber 1 and is monitored for energy by the first energy probe 9.

[0070] The temperature and humidity probe 19 and the first pressure gauge 20 are used to collect the temperature, humidity and pressure in the reaction chamber 1; the first air pump 21 is used to pump out the gas in the reaction chamber 1.

[0071] The absorption detection module includes a second light source 5, a third total reflection mirror 601, a fourth total reflection mirror 602, a first high reflection mirror 103, a second high reflection mirror 104, a first detector 7 and a first timing control module 8.

[0072] The absorption beam emitted by the second light source 5 is reflected by the third total reflection mirror 601 and the fourth total reflection mirror 602, then passes through the first high reflection mirror 103 at one end of the reaction chamber 1 and enters the reaction chamber 1. Since the free radicals absorb the beam of a certain wavelength, the absorption beam is reflected multiple times between the first high reflection mirror 103 and the second high reflection mirror 104 at both ends of the reaction chamber 1 and is absorbed by the free radicals at the same time. Subsequently, it passes through the second high reflection mirror 104 at the other end of the reaction chamber 1 and exits, and the first detector 7 is used to detect the change in the light intensity of the absorption beam in real time; the first timing control module 8 controls the first detector 7 to collect the intensity of the absorption beam at different moments after each passage of the absorption beam by setting the timing of the timing control card channel and using self-written software.

[0073] The fluorescence detection module includes a fluorescence chamber, a third light source 10, an optical fiber coupling module 11, a tapered aperture 12, a second energy probe 13, a free radical collection module 14, a second air pump 15, a second pressure gauge 16, a second detector 17 and a second timing control module 18.

[0074] The laser emitted by the third light source 10 is collimated by the optical fiber coupling module 11 and then enters the fluorescence cavity; the free radical collection module 14 collects the free radicals in the reaction cavity 1 in a jet manner through a nozzle with an extremely small aperture into the fluorescence cavity. The sampling port, i.e., the nozzle, is located directly below the intersection of the absorption beam and the photolysis beam. The free radical jet intersects with the collimated laser beam, and the free radicals at the intersection are excited by the laser to generate fluorescence signals; the second detector 17 is used to receive the fluorescence signals generated after the free radicals are excited by the laser; the second timing control module 18 controls the opening or closing of the second detector 17 by setting the timing of the timing control card channels and using self-written software; the second air pump 15 is used to pump out the gas in the fluorescence cavity; the second pressure gauge 16 is used to collect the pressure in the fluorescence cavity; the second energy probe 13 is used to monitor the energy of the laser emitted from the fluorescence cavity; conical diaphragms 12 with a certain diameter are respectively arranged at the light inlet end and the light outlet end of the fluorescence cavity, and the conical diaphragms 12 are used to reduce the interference of laser stray light on the signal collection in the fluorescence detection module.

[0075] The collection module includes an industrial control computer 26, which is used to receive various signals collected in the system and control various controllable devices; the industrial control computer 26 directly receives the signals of the first energy probe 9, the second energy probe 13, the first detector 7, the second detector 17, the temperature and humidity probe 19, the first pressure gauge 20, and the second pressure gauge 16; the industrial control computer 26 directly controls the flow rates of the first mass flow controller 2301, the second mass flow controller 2302, the third mass flow controller 2303, and the fourth mass flow controller 2304; the industrial control computer 26 is used to connect to the timing control card, and through the first timing control module 8 and the second timing control module 18, realizes the control of the opening and closing of the corresponding detectors in the absorption detection module and the fluorescence detection module to obtain the decay curve of the free radicals changing with time.

[0076] A measurement system for the reaction rate constant of free radical bimolecular reactions, and the principles of each part are as follows:

[0077] (1) Nitrogen 2401 is connected to the front end of the second mass flow controller 2302, and the back end is connected to the bubbler 25 to blow out the free radical precursor. The bubbler 25 contains the free radical precursor. The free radical precursor is combined with nitrogen 2401 (diluent gas) passing through the first mass flow controller 2301 to obtain the first synthesis gas. The concentration of the free radical precursor is adjusted by controlling the flow rate ratio of the two gases; oxygen 2402 passes through the third mass flow controller 2303 and the reaction gas 2403 for free radical bimolecular reaction passes through the fourth mass flow controller 2304 and is connected to a tee joint and then jointly connected to the reaction module with the first synthesis gas; the concentration of free radical generation is controlled by regulating the flow rates set by the above-mentioned various mass flow controllers.

[0078] (2) The photolysis beam (266nm laser) emitted by the first light source 3 enters the beam expander 2 after passing through the first total reflection mirror 401 and the second total reflection mirror 402. After passing through the beam expander 2, a larger-diameter and collimated light spot is generated. The photolysis beam enters the reaction chamber 1 through the lens with an anti-reflection coating, i.e., the first window 101. The larger-diameter photolysis beam can more fully and uniformly photolyze the radical precursor to generate sufficient radicals. The photolyzed beam passes through the same lens with an anti-reflection coating, i.e., the second window 102, and irradiates the first energy probe 9. The first energy probe 9 is used to monitor the energy of the 266nm laser to ensure the efficient photolysis of the radical precursor.

[0079] (3) The absorption detection module and the reaction module are in the same place. Using the absorption characteristics of radicals in the ultraviolet band, the concentration attenuation of radicals is indirectly detected and recorded. The absorption beam (ultraviolet light) emitted by the second light source 5 enters the reaction chamber 1 through the third total reflection mirror 601 and the fourth total reflection mirror 602. The absorption beam passes through the first highly reflective mirror 103 and is incident on the second highly reflective mirror 104 located opposite it. The absorption beam is reflected multiple times between the highly reflective mirrors 103 and 104 at both ends of the reaction chamber 1, and at the same time, the absorption detection of the radicals generated in the reaction chamber 1 is realized. Radicals absorb light beams of a certain wavelength, and the change in the light intensity of the absorption beam is detected in real time by the first detector 7. According to the change in the light intensity of the absorption beam and the Lambert-Beer absorption law, the change in the radical concentration in the reaction chamber 1 is calculated in real time. Using the absorption characteristics of the gas to be measured in a specific band, the transmitted light intensity attenuated in the optical resonator is collected to obtain the absorption spectrum, and the absorption spectrum is fitted to obtain the background decay time and decay time of the laser in the reaction chamber 1. The concentration of radicals in the reaction chamber 1 is obtained through the calculated decay time, and the change in the radical concentration in the reaction chamber 1 is calculated in real time. The calculation formula is as follows:

[0080]

[0081] Among them, X is the radical concentration measured in real time; R L is the effective cavity length, that is, the ratio of the cavity length to the single-pass absorption optical path length of the gas in the cavity; c is the speed of light; σ is the absorption cross-section of the gas to be measured; τ is the decay time when there are radicals in the reaction chamber 1, and τ 0 is the background decay time when there are no radicals in the reaction chamber 1;

[0082] The calculation formula for the decay time τ when there are radicals in the reaction chamber 1 is as follows:

[0083]

[0084] Among them, L is the cavity length, R is the reflectivity of the highly reflective mirror surface, and α is the absorption coefficient of the gas.

[0085] The background decay time τ of free radicals in the reaction chamber 1 0 The calculation formula is as follows:

[0086]

[0087] The first timing control module 8 controls the first detector 7 to turn on at a fixed time t after the ultraviolet light emission by setting the corresponding timing, 0 0 and turn on at t + △t after the next ultraviolet light emission, and so on to obtain the decay curve of the free radical concentration changing with time within a certain time range; the apparent activity of the free radical decay is obtained through exponential fitting. According to the input of different concentrations of precursors or reactants, the linear fitting of the free radical activities at different concentrations can be done again to obtain the decay rate constant of the free radical itself or the reaction rate constant of the bimolecular reaction between the free radical and a certain reactant. 0 Among them, the free radicals generated by photolyzing the free radical precursor react with the introduced reaction gas in a bimolecular reaction, and the free radical concentration decays with time. The exponential fitting is performed on the measured real-time free radical concentration X and the reaction time t. The exponential fitting formula is as follows:

[0088]

[0089]

[0090]

[0090] Among them, X t is the free radical concentration at time t, X 0 is the free radical concentration at the initial time; t is the reaction time, and k 1 is the apparent result of the free radical activity measured by the absorption detection module.

[0091] When the reaction gas is not introduced, the decay of free radicals in the system comes from the bimolecular collision reaction between free radicals. At this time, the result after exponential fitting is the free radical background activity ko of this system under this experimental condition. When measuring the bimolecular reaction activity of free radicals subsequently, the free radical background activity ko is used for linear fitting.

[0092] According to the steady-state approximation, the k 1 obtained by exponential fitting includes the free radical background activity ko and the activity kr of the free radical participating in the bimolecular reaction; kr is positively correlated with the reactant concentration. A gradient experiment is performed on the bimolecular reaction of different concentrations of reactants and free radicals, and a linear fitting is performed on the apparent activity k 1 and the reactant concentration Y. The slope obtained is the bimolecular reaction rate constant v of the free radical and the reaction gas, and the intercept is the background value ko of the instrument. The formula is as follows:

[0093] k 1 = ko + kr

[0094] kr = v × Y

[0095] (4) The fluorescence detection module is connected to the reaction module through a sampling nozzle, and is used to excite free radicals to generate fluorescence signals and collect fluorescence signals; in the reaction module, OH free radicals are generated by the dissociation of free radical single molecules, and there is a concentration relationship between free radicals and OH free radicals; in the fluorescence detection module, OH free radicals generated by the dissociation of free radical single molecules are excited by a 308 nm laser and undergo energy level transitions, and fluorescence signals are emitted during the transition process.

[0096] The third light source 10 emits a 308 nm laser, which enters the optical fiber after being focused by a lens. The light emitted from the optical fiber is collimated by the optical fiber coupling module 11 and then enters the fluorescence detection module; the free radical collection module 14 collects OH free radicals in the reaction chamber 1 in the form of a jet through a nozzle with a very small aperture; the OH free radical jet intersects with the collimated 308 nm laser beam, and the OH free radicals at the intersection are excited by the laser to generate fluorescence signals; the attenuation of the fluorescence signals is collected and recorded by the second detector 17; conical diaphragms 12 with a certain diameter are respectively arranged at the light inlet end and the light outlet end of the fluorescence chamber, and the conical diaphragms are used to reduce the interference of laser stray light on the collected signals in the fluorescence detection module. Since under low-pressure conditions, the fluorescence lifetime of OH free radicals excited by a 308 nm laser becomes longer, which is more conducive to signal collection, the second air pump 15 uses a commercial vacuum scroll dry pump to regulate the pressure of the fluorescence detection module. The pressure is monitored by the second pressure gauge 16. To ensure the efficient excitation of fluorescence signals, the second energy probe 13 is suspended at the center of the light outlet of the 308 nm laser through an adapter to monitor the energy intensity of the light outlet for real-time regulation. The second timing control module 18 controls the second detector 17 to perform multiple collections between adjacent two laser pulses, and controls the opening and closing of the second detector 17 through timing settings, ensuring that as many fluorescence signals as possible are collected while protecting the second detector 17 from being damaged by the laser, and then obtaining the fluorescence decay signals generated after the excitation of free radicals; the fluorescence signals are controlled by timing to enable the photon acquisition card in the industrial control computer 26 to start acquisition and close after the acquisition is completed.

[0097] The free radicals generated by the photolysis precursor react with the introduced reaction gas in a bimolecular reaction, and the concentration of free radicals decays with time. A double-exponential fitting is performed on the fluorescence photon decay signals of OH free radicals measured in real time. The double-exponential fitting formula of the fluorescence signals is as follows:

[0098]

[0099] where, S radical is the fluorescence signal measured in real time, A 0 , A 1 and a are all parameters of the double-exponential fitting;,, k 2is the apparent result of the radical activity measured by the fluorescence detection module, and t is the reaction time;

[0100] When the reaction gas is not introduced, the decay of radicals in the system comes from the bimolecular collision reaction between radicals. At this time, the result after exponential fitting is the free radical background activity ko of this system under this experimental condition. When measuring the bimolecular reaction activity of radicals subsequently, the free radical background activity ko is used for linear fitting.

[0101] According to the steady-state approximation, the k of double-exponential fitting is derived 2 includes the background signal ko and the activity kr of the radicals participating in the bimolecular reaction; kr is positively correlated with the reactant concentration. Gradient experiments are performed on the bimolecular reactions of reactants with different concentrations and radicals, and the apparent activity k 2 is linearly fitted with the reactant concentration Y, and the obtained slope is the bimolecular reaction rate constant v of the radicals with this reaction gas, and the intercept is the background value ko of the instrument. The formula is as follows:

[0102] k 2 = ko + kr

[0103] kr = v × Y

[0104] Example 2

[0105] A method for measuring the bimolecular reaction rate constant of radicals using the system of the present invention is as follows:

[0106] Step 1. Measurement of free radical background activity ko and verification of system stability: Only introduce the radical precursor into the reaction chamber 1, measure the free radical background activity ko, and verify the system stability according to the free radical background activity ko measured under different measurement methods (based on the absorption detection module and based on the fluorescence detection module).

[0107] Specifically as follows:

[0108] S11, load the radical precursor (diiodomethane CH 2 I 2 ) into the bubbler 25, turn on the first air pump 21 and the second air pump 15, so that the fluorescence detection module is first in a low-pressure state to avoid affecting the normal measurement of the fluorescence signal; turn on the first light source 3, the second light source 5, and the third light source 10, so that the photolysis beam and the absorption beam for photolyzing the precursor enter the reaction chamber 1, and the fluorescence detection beam enters the fluorescence detection module.

[0109] S12, turn on the first mass flow controller 2301, the second mass flow controller 2302, and the third mass flow controller 2303 through the industrial control computer 26.

[0110] S13. In the case where no reaction gas is introduced, the free radicals generated by the photolysis of the radical precursor by the first light source 3 undergo bimolecular reactions with themselves, and the concentration of free radicals decays with time.

[0111] S14. The absorption detection module measures the change in the light intensity of the absorption beam and calculates in real time the change in the concentration of free radicals in the reaction chamber 1 according to the Lambert-Beer law; by using the absorption characteristics of the gas to be measured in a specific wavelength band, the attenuated transmitted light intensity in the optical resonator is collected to obtain the absorption spectrum, and the absorption spectrum is fitted to obtain the background decay time and the decay time of the laser in the reaction module; the concentration of free radicals in the reaction chamber 1 is obtained through the decay time, and the change in the concentration of free radicals in the reaction chamber 1 is calculated in real time. The concentration calculation formula is as follows:

[0112]

[0113] Where X is the concentration of free radicals measured in real time; R L is the effective cavity length, that is, the ratio of the cavity length to the single-pass absorption optical path length of the gas in the cavity; c is the speed of light; σ is the absorption cross-section of the gas to be measured; τ is the decay time when there are free radicals in the reaction chamber 1, and τ 0 is the background decay time when there are no free radicals in the reaction chamber 1.

[0114] An exponential fit is performed on the concentration X of the free radicals measured in real time and the reaction time t. The exponential fit formula is as follows:

[0115]

[0116] Where X t is the concentration of free radicals at time t, and X 0 is the concentration of free radicals at the initial time; k0 1 is the free radical background activity obtained by the first measurement method (the measurement method based on the absorption detection module).

[0117] S15. The fluorescence detection module measures and collects the real-time fluorescence photon decay signal; the reaction activity of the free radicals themselves is obtained through double exponential fitting. The double exponential fitting formula of the fluorescence signal is as follows:

[0118]

[0119] Where S radical is the fluorescence signal measured in real time, and A 0 , A 1 and a are all parameters of the double exponential fitting; k0 2 is the free radical background activity obtained by the second measurement method (the measurement method based on the fluorescence detection module).

[0120] S16. The free radical basic activity ko is obtained through multiple groups of experiments and exponential fitting to verify the stability of the system itself. Based on the free radical basic activities obtained by the two measurement methods, they can be mutually verified. If the difference in the free radical activities obtained by the two measurement methods does not exceed the set threshold, it indicates that the measurement result of the free radical activity is reliable; otherwise, it indicates that the measurement result of the free radical activity is unreliable.

[0121] Step 2: Introduce free radical precursors and reactants with different concentrations into the reaction chamber 1, measure the activity of free radicals participating in the bimolecular reaction, and obtain the free radical activity k at different reactant concentrations.

[0122] S21. Turn on the first air pump 21 and the second air pump 15; turn on the first light source 3, the second light source 5, and the third light source 10, so that the photolysis light beam and absorption light beam for photolyzing the precursor enter the reaction module, and the fluorescence detection light beam enters the fluorescence detection module.

[0123] S22. Through the industrial control computer 26, turn on the first mass flow controller 2301 and the second mass flow controller 2302 for controlling the inlet flow rates of the synthesis gas and the dilution gas 2401, turn on the third mass flow controller 2303 for controlling the flow rate of oxygen 2402, and turn on the fourth mass flow controller 2304 for controlling the reaction gas 2403.

[0124] S23. The free radicals generated by the photolysis of the precursor by the first light source 3, under the condition of introducing the reaction gas, the bimolecular reaction occurs between them, and the free radical concentration decays with time.

[0125] S24. The absorption detection module measures the change in the light intensity of the absorption light beam and calculates the decay time according to the Lambert-Beer law, inversely obtains the free radical concentration, and performs exponential fitting on the real-time measured free radical concentration X and the reaction time t. The exponential fitting formula is as follows:

[0126]

[0127] where k 1 is the free radical activity obtained by the first measurement method (the measurement method based on the absorption detection module).

[0128] S25. The fluorescence detection module measures and collects the decay signal of the fluorescence photons; the reaction activity of the free radicals in the bimolecular reaction is obtained through double exponential fitting. The double exponential fitting formula of the fluorescence signal is as follows:

[0129]

[0130] where k 2 is the free radical activity obtained by the second measurement method (the measurement method based on the fluorescence detection module).

[0131] Step 3: Perform linear fitting based on the measured free radical basic activity ko and the radical activities k at different reactant concentrations, and the bimolecular reaction rate constant of the free radicals can be obtained. The fitting expression is: k = ko + v × Y; where v is the bimolecular reaction rate constant of the free radicals.

[0132] Among them, the free radical basic activity ko obtained according to the first method 1 and the radical activities k at different reactant concentrations 1 are subjected to linear fitting to obtain the bimolecular reaction rate constant v of the free radicals 1 ; the free radical basic activity ko obtained according to the second method 2 and the radical activities k at different reactant concentrations 2 are subjected to linear fitting to obtain the bimolecular reaction rate constant v of the free radicals 2 . In this embodiment, the bimolecular reaction rate constants of the free radicals obtained by the two measurement methods can be mutually verified, and the test results of one of the measurement methods can be selected or the test results of the two measurement methods can be weighted and fused.

[0133] Since the bimolecular reaction rate constant of the free radicals with SO 2 (reactant) has been fully verified, therefore, in this embodiment, the reactant introduced is SO 2 gas, and the accuracy of the present invention can be verified by using the measured bimolecular reaction rate constant v.

[0134] It has been found through experiments that the fluorescence detection result is more accurate and can exclude the interference of absorption spectral lines. Therefore, when measuring the free radical basic activity, the free radical basic activity obtained by the fluorescence detection module (the second measurement method) is used as the reference. When there is a difference between the background result of absorption detection and the background result of fluorescence detection, the background value of the fluorescence detection result is selected and incorporated into the subsequent use of the absorption detection method. The advantage is that it can ensure the accuracy of the background and eliminate the interference spectral line problem that may occur in absorption detection.

[0135] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A free radical bimolecular reaction rate constant measurement system, characterized in that: The system includes: Injection module (22), reaction module, absorption detection module, fluorescence detection module, collection module; The injection module (22) is connected to the reaction module and is used to introduce free radical precursors and / or reactants into the reaction chamber (1) of the reaction module; The reaction module uses a photolysis beam to photolyze a free radical precursor in the reaction chamber (1) to generate free radicals; The absorption detection module is used to emit an absorption light beam to the reaction chamber (1) to be absorbed by the free radicals, and to collect the absorption light beam signal after being absorbed by the free radicals; The fluorescence detection module is used to collect the free radicals generated by the reaction module into the fluorescence cavity, emit laser to the fluorescence cavity to excite the free radicals to generate fluorescence signals, and collect the fluorescence signals; The acquisition module is used to receive various signals collected in the system and monitor various controllable devices in the system, and calculate the free radical bimolecular reaction rate constant according to the detected signals.

2. A free radical bimolecular reaction rate constant measurement system according to claim 1, characterized in that: The sample injection module (22) comprises: a bubbling bottle (25) containing a free radical precursor, a blowing gas, a diluent gas, oxygen and a reaction gas; The blowing gas is connected to the bubbling bottle (25) through the second mass flow controller (2302) to blow out the free radical precursor in the bubbling bottle (25); The dilution gas passes through the first mass flow controller (2301) and is combined with the free radical precursor blown out of the bubbling bottle (25) to dilute the free radical precursor to obtain a first synthesis gas; The oxygen passes through a third mass flow controller (2303), and the reaction gas passes through a fourth mass flow controller (2304) and is combined with the first synthesis gas to obtain a second synthesis gas; The second synthesis gas is introduced into the reaction chamber (1) of the reaction module.

3. A free radical bimolecular reaction rate constant measurement system according to claim 1, characterized in that: The reaction module (1) comprises: a reaction chamber (1), a first window (101), a second window (102), a first light source (3), a beam expander (2), a first energy probe (9), a temperature and humidity probe (19), a first pressure gauge (20), and a first air pump (21); The photolysis light beam emitted by the first light source (3) is collimated by a beam expander (2), and after the light spot diameter is enlarged, it is emitted into the reaction chamber (1) through a first window (101) at one end of the reaction chamber (1), and the free radical precursor in the reaction chamber (1) is photolyzed to generate free radicals. Subsequently, the photolysis light beam is emitted through a second window (102) at the other end of the reaction chamber (1), and energy is monitored by a first energy probe (9); The temperature and humidity probe (19) and the first pressure gauge (20) are used to collect the temperature, humidity and pressure in the reaction chamber (1); and the first air pump (21) is used to extract the gas in the reaction chamber (1).

4. A free radical bimolecular reaction rate constant measurement system according to claim 1, characterized in that: The absorption detection module comprises a second light source (5), a first high-reflection mirror (103), a second high-reflection mirror (104), a first detector (7) and a first timing control module (8); The absorption light beam emitted by the second light source (5) passes through the first high-reflection mirror (103) at one end of the reaction chamber (1) and is emitted into the reaction chamber (1), is reflected multiple times between the first high-reflection mirror (103) and the second high-reflection mirror (104) at both ends of the reaction chamber (1), and is absorbed by free radicals at the same time, and then is emitted through the second high-reflection mirror (104) at the other end of the reaction chamber (1), and the absorption light beam signal is collected by the first detector (7); the first timing control module (8) is used to control the first detector (7) to collect the corresponding absorption light beam intensity at different times after each absorption light beam is emitted.

5. A free radical bimolecular reaction rate constant measurement system according to claim 1, characterized in that: The fluorescence detection module comprises a fluorescence cavity, a third light source (10), an optical fiber coupling module (11), a second energy probe (13), a free radical collection module (14), a second air pump (15), a second pressure gauge (16), a second detector (17) and a second timing control module (18); The laser light emitted by the third light source (10) is collimated by the optical fiber coupling module (11) and then enters the fluorescent cavity; the free radical collection module (14) uses a nozzle to collect the free radicals in the reaction cavity (1) into the fluorescent cavity in a jet manner; the free radicals in the fluorescent cavity generate fluorescent signals after being excited by the laser light; the second detector (17) is used to collect the fluorescent signals; the second timing control module (18) is used to control the opening or closing of the second detector (17); the second air pump (15) is used to extract the gas in the fluorescent cavity; the second pressure gauge (16) is used to collect the pressure in the fluorescent cavity; and the second energy probe (13) is used to monitor the energy of the laser light emitted from the fluorescent cavity.

6. A method for measuring a free radical bimolecular reaction rate constant, characterized in that: A free radical bimolecular reaction rate constant measurement system applicable to any one of claims 1 to 5 above, the method is as follows: Step 1, only the free radical precursor is introduced into the reaction chamber (1), and the free radical activity measured at this time is the reaction activity of the free radical itself, that is, the free radical bottom activity ko; Step 2: introducing a free radical precursor and reactants of different concentrations into the reaction chamber (1), and measuring the free radical activity k at different reactant concentrations, wherein Y is the reactant concentration; Step 3: Linear fitting is performed based on the measured free radical activity ko and the free radical activity k at different reactant concentrations to obtain the bimolecular reaction rate constant of the free radical. The fitting expression is: k=ko+v×Y; where v is the bimolecular reaction rate constant of the free radical.

7. A method for measuring a free radical bimolecular reaction rate constant according to claim 6, characterized in that: There are two ways to measure free radical activity: The first method is to calculate the free radical concentration based on the absorption beam signal collected by the absorption detection module; and based on the change of the free radical concentration, the free radical activity is fitted; The second method is to fit the free radical activity based on the fluorescence signal collected by the fluorescence detection module and the change of the fluorescence signal; Based on the two measurement methods, the measurement results of free radical activity are mutually verified. If the difference in free radical activity obtained by the two measurement methods does not exceed the set threshold, it means that the measurement result of free radical activity is reliable, and the test result of one of the measurement methods is selected or the test results of the two measurement methods are weighted and fused; otherwise, it means that the measurement result of free radical activity is unreliable.

8. A method for measuring a free radical bimolecular reaction rate constant according to claim 7, characterized in that: The first measurement method is as follows: The change in the intensity of the absorption beam is detected, and the free radical concentration is measured in real time according to the Lambert-Beer law. The calculation formula is as follows: Where X is the free radical concentration measured in real time; R L is the effective cavity length, i.e., the ratio of the cavity length to the single absorption optical path length of the gas in the cavity; c is the speed of light; σ is the absorption cross section of the gas to be measured; τ is the ring-down time when there are free radicals in the reaction cavity (1), and τ0 is the background ring-down time when there are no free radicals in the reaction cavity (1); The free radical concentration X measured in real time is exponentially fitted with time t, and the exponential fitting formula is: Among them, X t is the free radical concentration at time t, X0 is the free radical concentration at the initial time; k1 is the free radical activity obtained by the first measurement method.

9. A method for measuring a free radical bimolecular reaction rate constant according to claim 7, characterized in that: The second measurement method is as follows: The real-time measured fluorescence signal and time t were subjected to a double exponential fitting, and the double exponential fitting formula was: Among them, S radical is the fluorescence signal measured in real time, A0, A1 and a are the parameters of double exponential fitting; k2 is the free radical activity obtained by the second measurement method.

10. A computer program product, characterized in that It includes a computer program / instruction, which, when executed by a processor, implements a method for measuring a free radical bimolecular reaction rate constant as described in any one of claims 6-9.

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