A free radical bimolecular reaction rate constant measurement system and method

Abstract

The present invention discloses a free radical bimolecular reaction rate constant measurement system and method, which relates to the field of atmospheric environment measurement technology. Free radical precursors and / or reactants are introduced into a reaction chamber, a photolysis beam is used to photolyze the free radical precursors to produce free radicals, an absorption detection module emits an absorption beam into the reaction chamber, which is absorbed by the free radicals and collects the absorption beam signal, a fluorescence detection module collects the free radicals generated by the reaction module into a fluorescence chamber, and emits a laser into the fluorescence chamber to excite the free radicals to produce a fluorescence signal and collect the fluorescence signal; the free radical concentration change is measured based on the light intensity change of the absorption beam and the free radical activity is obtained, and the free radical activity is obtained based on the change in the fluorescence signal, and the two methods are mutually verified; the free radical base activity in the absence of reactants and the free radical activity under different reactant concentrations are measured, and a linear fit is performed to obtain the free radical bimolecular reaction rate constant. The present invention solves the problem of large errors in free radical bimolecular reaction rates.

Description

Technical Field

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

[0002] Free radicals in the atmosphere rapidly transform primary pollutants into secondary pollutants, determining the level of atmospheric oxidizing properties. However, the reactions of free radicals with some atmospheric trace gases (such as Kriging radicals) are not well understood, and research has only begun in recent years. First, some research groups have achieved laboratory measurements of the kinetics of free radical bimolecular reactions using methods such as vacuum ultraviolet photoionization mass spectrometry, ultraviolet absorption spectroscopy, laser-induced fluorescence, and infrared-visible spectroscopy. Measurements of free radical reaction rate constants have been conducted directly, indirectly, and theoretically, but the results are often inconsistent across different methods and measurement systems. Second, research on the measurement of free radical bimolecular reaction rate constants is relatively limited, and some bimolecular reaction results are conflicting, requiring further investigation. Accurately measuring the bimolecular reaction rate constants of free radicals with atmospheric trace gases is crucial for the accurate quantification of atmospheric oxidizing properties. Furthermore, fundamental data on free radicals are scarce, so measurements of their rate constants can be used to supplement fundamental model parameters.

[0003] Exploring the kinetics of bimolecular reactions of free radicals is of scientific significance for improving the study of atmospheric oxidizability and the causes of secondary pollutants. It is necessary to develop a device and method that can directly measure the bimolecular reaction rate constants of free radicals and various primary pollutants using different detection methods in the same system. Summary of the Invention

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

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

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

[0007] The injection 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 to the reaction chamber to be absorbed by the free radicals, and collect the absorption beam signal after being absorbed by the free radicals;

[0010] The fluorescence detection module is used to collect the free radicals generated by the reaction module into the fluorescence cavity, emit laser into the fluorescence cavity to excite the free 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 free radical bimolecular reaction rate constant based on the detected signals.

[0012] Preferably, the sampling module comprises: a bubbling bottle filled with a free radical precursor, a blowing gas, a diluent gas, oxygen and a reaction gas;

[0013] The blowing gas is connected to the bubbling bottle through a second mass flow controller to blow out the free radical precursors in the bubbling bottle;

[0014] The dilution gas passes through a first mass flow controller and is combined with the free radical precursor blown out of the bubbling bottle to dilute the free 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, a beam expander, 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 and expanded, and after the spot diameter is enlarged, it is emitted into the reaction chamber through a first window at one end of the reaction chamber, and the free radical precursor in the reaction chamber is photodecomposed to produce free radicals. The photolysis beam is then emitted through a second window at the other end of the reaction chamber, and the energy is monitored by a 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 extract the gas in the reaction chamber.

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

[0021] The absorption beam emitted by the second light source passes through the first high-reflection mirror at one end of the reaction chamber and enters the reaction chamber, is reflected multiple times between the first high-reflection mirror and the second high-reflection mirror at both ends of the reaction chamber and is absorbed by free radicals at the same time, and then passes through the second high-reflection mirror at the other end of the reaction chamber and is emitted, 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 corresponding absorption beam intensity at different times after each absorption beam is emitted.

[0022] Preferably, the fluorescence detection module includes a fluorescence cavity, a third light source, a 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 fluorescent cavity; the free radical collection module uses a nozzle to collect the free radicals in the reaction cavity in a jet manner into the fluorescent cavity; the free radicals in the fluorescent cavity generate a fluorescent signal after being excited by the laser; the second detector is used to collect the fluorescent signal; the second timing control module is used to control the opening or closing of the second detector; the second air pump is used to extract the gas in the fluorescent cavity; the second pressure gauge is used to collect the pressure in the fluorescent cavity; and the second energy probe is used to monitor the energy of the laser emitted through the fluorescent cavity.

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

[0025] Step 1: Only the free radical precursor is introduced into the reaction chamber. 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;

[0026] Step 2: introducing a free radical precursor and reactants of different concentrations into the reaction chamber, and measuring 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 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.

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

[0029] 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 free radical concentration, the free radical activity is fitted;

[0030] 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;

[0031] 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.

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

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

[0034]

[0035] Where X is the free radical concentration measured in real time; R L is the effective cavity length, that is, the ratio of the cavity length to the optical path length of a single absorption 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, and τ0 is the background ring-down time when there are no free radicals in the reaction cavity;

[0036] The free radical concentration X measured in real time is subjected to exponential fitting with time t. The exponential fitting formula is:

[0037]

[0038] 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.

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

[0040] The real-time fluorescence signal was fitted with a double exponential fitting with time t. The double exponential fitting formula is:

[0041]

[0042] Among them, S radical is the real-time fluorescence signal, A0, A1 and a are the parameters of the double exponential fitting; k2 is the free radical activity obtained by the second measurement method.

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

[0044] The advantages of the present invention are:

[0045] (1) The present invention solves the problem of large errors in the bimolecular reaction rate of free radicals. For the same reaction state of free radicals, the bimolecular reaction rate constants of free radicals and atmospheric pollutants are measured synchronously through different technologies, combining the advantages of different measurement technologies to improve the accuracy of measurement.

[0046] (2) The free radical bimolecular reaction rate constant is measured by combining fluorescence detection and absorption detection. Both methods are highly sensitive absolute measurement methods. The measurement results of the two methods can be verified by each other, avoiding the interference of absorption spectrum overlap that may be caused by relying solely on the absorption detection method.

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

[0048] (4) In the actual measurement process of the free radical bimolecular reaction rate constant by combining fluorescence detection and absorption detection, free radical precursors and reactants participating in the free radical bimolecular reaction are introduced into the reaction module, and the activity values ​​under different concentration gradients are obtained by adjusting the reactant concentrations. The reactant concentrations at different gradients are linearly fitted with the apparent reaction activity to obtain the free radical bimolecular reaction rate constant; on the premise that the accurate free radical base activity has been obtained, the accuracy of the bimolecular reaction rate constant obtained by the two methods is also ensured.

[0049] (5) A hexagonal reaction chamber with dual measurement modes was designed, with air entering from the center and light entering from both sides. This ensures that the two methods achieve consistency in measuring the sampled gas while measuring all sampled gases as much as possible. Secondly, the light entering from both sides is achieved through two windows and two fully reflective mirrors. The absorption beam and the photolysis beam intersect in the reaction chamber, and the photolysis of the precursor and the detection of the free radical concentration are completed at the intersection of the beams, thus ensuring the accuracy of the free 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 contacts the intersection of the beams, thereby realizing real-time detection of the free radical concentration. Therefore, this design result ensures the simultaneous realization of precursor dissociation, free radical generation, free radical absorption detection, and free radical fluorescence detection. In addition, the window and the total reflector are equipped with customized pressure sheets and pressure rings, which ensure the airtightness of the reaction module. Good airtightness ensures the stability of the measurement results.

[0051] (7) Design and implement a timing control module for continuous dual measurement, 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, turning on at a certain time t0 after the ultraviolet light is emitted, and turning on at time t0+△t after the next ultraviolet light is emitted. After accumulating a certain amount of △t, the decay curve of the free radical concentration over 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, thereby obtaining the fluorescence decay signal generated after free radical excitation. This type of timing control setting ensures the synchronous and continuous detection of the two measurement methods and also achieves the purpose of protecting the detector from laser damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of a free radical bimolecular reaction rate constant measurement system.

[0053] Figure 2 Schematic diagram of the fluorescence detection module.

[0054] Figure 3 Schematic diagram of the reaction module.

[0055] Description of reference numerals:

[0056] 1-reaction chamber, 2-beam expansion, 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 coupling module, 12-conical aperture, 13-second energy probe, 14-free radical Acquisition 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-injection module, 2301-first mass flow controller, 2302-second mass flow controller, 2303-third mass flow controller, 2304-fourth mass flow controller, 2401-dilution gas, 2402-oxygen, 2403-reaction gas, 25-bubbling bottle, 26-industrial computer. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] Example 1

[0059] like Figure 1-3 As shown, a free radical bimolecular reaction rate constant measurement system includes a sampling module 22, a reaction module, an absorption detection module, a fluorescence detection module, and a collection module.

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

[0061] The reaction module is used for generating free radicals, and utilizes a photolysis beam to photolyze free radical precursors in the reaction chamber 1 to generate free radicals.

[0062] The absorption detection module emits an absorption beam into the reaction chamber 1, which is absorbed by the free radicals. The absorption beam signal after absorption by the free radicals is collected and used to measure the free radical concentration at a certain wavelength. The absorption detection module and the reaction module are located in the same mechanical structure.

[0063] The fluorescence detection module collects free radicals generated by the reaction module into a fluorescence cavity. Laser light is emitted into the cavity to excite the free radicals, generating a fluorescence signal. This signal is then collected while monitoring the energy intensity of the emitted laser light. The fluorescence detection module is located on the lower left side of the reaction module and is connected to the reaction module via a mechanical adapter and screws.

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

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

[0066] The 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 diluent gas, a purge gas, oxygen 2402, and a reaction gas (reactant) 2403, and a bubbling bottle 25 containing a free radical precursor (such as diiodomethane (CH2I2)). In this embodiment, the diluent gas and the purge gas are both nitrogen 2401.

[0067] Nitrogen 2401, acting as a blowing gas, is introduced into the blowing bottle 25 through the second mass flow controller 2302 to blow out a free radical precursor. Nitrogen 2401, acting as a diluent gas, is passed through the first mass flow controller 2301 and combined with the free radical precursor blown out of the blowing bottle 25 to produce a first synthesis gas. The concentration of the free radical precursor is adjusted by controlling the flow ratio of the two gases. Oxygen passes through a third mass flow controller (2303), and the reaction gas passes through a fourth mass flow controller (2304). Afterwards, the oxygen is combined with the first synthesis gas through a three-way connector to produce a second synthesis gas. The second synthesis gas is introduced into the reaction chamber 1 of the reaction module.

[0068] The reaction module includes a reaction chamber 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] Reaction chamber 1 is a chamber for generating free radicals. Reaction chamber 1 has a hexagonal cross-section, with air entering the center and light entering from both sides. The photolysis beam emitted by first light source 3 passes through first total reflection mirrors 401 and 402, then enters beam expander 2. After being collimated and having its spot diameter expanded by beam expander 2, it is then emitted into reaction chamber 1 through first window 101 at one end of reaction chamber 1. With this expanded spot diameter, the photolysis beam can more fully photodecompose free radical precursors to produce sufficient free radicals. The photolysis beam then exits through second window 102 at the other end of reaction chamber 1, where its energy is monitored by 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 extract 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 light beam emitted by the second light source 5 is reflected by the third total reflection mirror 601 and the fourth total reflection mirror 602, and then enters the reaction chamber 1 through the first high-reflection mirror 103 at one end of the reaction chamber 1. Since free radicals absorb light beams of a certain wavelength, the absorption light 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. It then passes through the second high-reflection mirror 104 at the other end of the reaction chamber 1 and is emitted. The intensity change of the absorption light beam is detected in real time by the first detector 7. The first timing control module 8 controls the first detector 7 to collect the corresponding absorption light beam intensity at different times after each absorption light beam passes through by setting the timing of the timing control card channel and using self-compiled software.

[0073] The fluorescence detection module includes a fluorescence cavity, a third light source 10, a fiber coupling module 11, a conical 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 light emitted by the third light source 10 is collimated by the fiber coupling module 11 and then enters the fluorescence cavity. The free radical collection module 14 collects the free radicals in the reaction chamber 1 into the fluorescence cavity in the form of a jet through an extremely small nozzle. 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 the collimated laser beam, and the free radicals at the intersection are excited by the laser to produce a fluorescence signal. The second detector 17 is used to receive the fluorescence signal generated by the free radicals excited by the laser. The second timing control module 18 controls the opening and closing of the second detector 17 by setting the timing of the timing control card channel and using self-programmed software. The second air pump 15 is used to pump gas from 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 light emitted from the fluorescence cavity. The fluorescence cavity is provided with a conical aperture 12 of a certain diameter at the light input and light output ends, respectively. The conical aperture 12 is used to reduce the interference of laser stray light on the signal collected by the fluorescence detection module.

[0075] The acquisition module includes an industrial computer 26, which is used to receive various signals collected in the system and control various controllable devices; the industrial computer 26 directly receives signals from 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 computer 26 directly controls the flow 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 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, it controls 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 free radical bimolecular reaction rate constant measurement system, the principles of each part are as follows:

[0077] (1) The front end of the second mass flow controller 2302 is connected to nitrogen 2401, and the rear end is connected to the bubbling bottle 25 to blow out free radical precursors. The bubbling bottle 25 is filled with free radical precursors. The free radical precursors are combined with the nitrogen 2401 (diluent gas) passing through the first mass flow controller 2301 to obtain the first synthesis gas. The concentration of the free radical precursors is regulated by controlling the flow ratio of the two gases; the oxygen 2402 is connected to a three-way through the third mass flow controller 2303 and the reaction gas 2403 used for bimolecular reaction of free radicals through the fourth mass flow controller 2304, and then connected to the reaction module together with the first synthesis gas; the concentration of free radicals generated is controlled by adjusting the flow setting of each of the above 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, and generates a larger diameter and collimated light spot after the beam expander 2. The photolysis beam enters the reaction chamber 1 through the lens coated with an anti-reflection film, namely the first window 101; the photolysis beam with a larger diameter can more fully and evenly photolyze the free radical precursor and generate sufficient free radicals; the light beam after photolysis passes through the same lens coated with an anti-reflection film, namely the second window 102, and irradiates the first energy probe 9; the first energy probe 9 is used to monitor the 266nm laser energy to ensure efficient photolysis of the free radical precursor.

[0079] (3) The absorption detection module and the reaction module are located in the same place, and the absorption characteristics of free radicals in the ultraviolet band are used to indirectly detect and record the concentration decay of free radicals. 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, and then passes through the first high-reflection mirror 103 and is incident on the second high-reflection mirror 104 located opposite it. The absorption beam is reflected multiple times between the high-reflection mirrors 103 and 104 at both ends of the reaction chamber 1, and absorption detection is simultaneously performed on the free radicals generated in the reaction chamber 1. Free radicals absorb light beams of a certain wavelength, and the intensity change of the absorption beam is detected in real time by the first detector 7. Based on the intensity change of the absorption beam and the Lambert-Beer absorption law, the change in the free radical concentration in the reaction chamber 1 is calculated in real time. The absorption characteristics of the gas to be measured in a specific wavelength band are used to collect the attenuated transmitted light intensity in the optical resonant cavity and then obtain an absorption spectrum. The absorption spectrum is fitted to obtain the background ring-down time and ring-down time of the laser in the reaction chamber 1. The concentration of free radicals in the reaction chamber 1 is obtained by calculating the ring-down time, and the change in the free radical concentration in the reaction chamber 1 is calculated in real time. The calculation formula is as follows:

[0080]

[0081] Where X is the free radical concentration measured in real time; R Lis the effective cavity length, that is, the ratio of the cavity length to the optical path length of a single absorption 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;

[0082] The formula for calculating the ring-down time τ when there are free radicals in the reaction chamber 1 is as follows:

[0083]

[0084] Where L is the cavity length, R is the reflectivity of the high-reflection mirror, and α is the absorption coefficient of the gas.

[0085] The calculation formula for the background ring-down time τ0 without free radicals in the reaction chamber 1 is as follows:

[0086]

[0087] The first timing control module 8 controls the first detector 7 to turn on at a fixed time t0 after the ultraviolet light is emitted by setting the corresponding timing, and to turn on at time t0+△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 by exponential fitting, and according to the input of different concentrations of precursors or reactants, the free radical activity at different concentrations can be linearly fitted 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.

[0088] The free radicals generated by the photolysis of the free radical precursor undergo a bimolecular reaction with the introduced reaction gas, and the free radical concentration decays over time. The real-time measured free radical concentration X and the reaction time t are subjected to an exponential fitting. The exponential fitting formula is as follows:

[0089]

[0090] Among them, X t is the free radical concentration at time t, X0 is the free radical concentration at the initial time; t is the reaction time, and k1 is the apparent result of the free radical activity measured by the absorption detection module.

[0091] When no reaction gas is introduced, the decay of free radicals in the system results from bimolecular collisions between free radicals. The result of exponential fitting is the free radical activity (ko) of the system under these experimental conditions. This free radical activity (ko) is used for linear fitting in subsequent measurements of free radical bimolecular reaction activity.

[0092] According to the steady-state approximation, the exponential fitting k1 includes the free radical base activity ko and the activity kr of the free radical participating in the bimolecular reaction; kr is positively correlated with the reactant concentration. Gradient experiments are performed on the bimolecular reactions of reactants with free radicals at different concentrations. A linear fit is performed on the apparent activity k1 and the reactant concentration Y. The slope obtained is the bimolecular reaction rate constant v of the free radical and the reactant gas, and the intercept is the background value ko of the instrument. The formula is as follows:

[0093] k1=ko+kr

[0094] kr=v×Y

[0095] (4) The fluorescence detection module is connected to the reaction module through a sampling nozzle, which is used to excite free radicals to generate fluorescence signals and collect fluorescence signals; in the reaction module, the free radical single molecule dissociates to generate OH free radicals, and there is a concentration relationship between the free radicals and the OH free radicals; in the fluorescence detection module, the OH free radicals generated from the free radical single molecule dissociation undergo energy level transition after being excited by the 308nm laser, and the emission during the transition generates a fluorescence signal.

[0096] A third light source 10 emits a 308nm laser beam, which is focused by a lens and then enters an optical fiber. The optical fiber's output light is collimated by a fiber coupling module 11 and then enters a fluorescence detection module. A free radical collection module 14 collects OH radicals in the reaction chamber 1 as a jet through a very small nozzle. The OH radical jet intersects the collimated 308nm laser beam, where the OH radicals are excited by the laser to produce a fluorescence signal. The decay of the fluorescence signal is collected and recorded by a second detector 17. The fluorescence chamber is equipped with conical apertures 12 of a certain diameter at both the light inlet and light outlet ends. These apertures are used to reduce interference from stray laser light on the signal collected by the fluorescence detection module. Because the fluorescence lifetime of OH radicals excited by the 308nm laser is prolonged under low pressure, facilitating signal collection, a second air pump 15, a commercial vacuum vortex dry pump, is used to control the pressure in the fluorescence detection module. The pressure is monitored by a second pressure gauge 16. To ensure efficient fluorescence signal excitation, a second energy probe 13 is suspended in the center of the 308nm laser light outlet using an adapter to monitor the energy intensity at the outlet for real-time control. The second timing control module 18 controls the second detector 17 to perform multiple acquisitions between two adjacent laser pulses, and controls the opening and closing of the second detector 17 through timing settings to ensure that as many fluorescence signals as possible are collected while also protecting the second detector 17 from damage by the laser, thereby obtaining a fluorescence attenuation signal generated after free radical excitation; the fluorescence signal is controlled by timing to enable the photon acquisition card in the industrial computer 26 to start acquisition and close after acquisition is completed.

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

[0098]

[0099] Among them, S radical is the real-time fluorescence signal, A0, A1 and a are the parameters of the double exponential fitting; k2 is the apparent result of free radical activity measured by the fluorescence detection module, and t is the reaction time;

[0100] When no reaction gas is introduced, the decay of free radicals in the system results from bimolecular collisions between free radicals. The result of exponential fitting is the free radical activity (ko) of the system under these experimental conditions. This free radical activity (ko) is used for linear fitting in subsequent measurements of free radical bimolecular reaction activity.

[0101] Based on the steady-state approximation, the biexponential fitting k2 is derived to include the background signal ko and the activity kr of the free radical participating in the bimolecular reaction; kr is positively correlated with the reactant concentration. Gradient experiments are performed on the bimolecular reaction of reactants with free radicals at different concentrations. A linear fit is performed on the apparent activity k2 and the reactant concentration Y. The slope obtained is the bimolecular reaction rate constant v of the free radical and the reactant gas, and the intercept is the background value ko of the instrument. The formula is as follows:

[0102] k2=ko+kr

[0103] kr=v×Y

[0104] Example 2

[0105] The method for measuring the free radical bimolecular reaction rate constant using the system of the present invention comprises the following steps:

[0106] Step 1: Measurement of free radical activity (ko) and verification of system stability: Only free radical precursors are introduced into the reaction chamber 1, and the free radical activity (ko) is measured. The system stability is verified based on the free radical activity (ko) measured under different measurement methods (based on the absorption detection module and based on the fluorescence detection module).

[0107] The details are as follows:

[0108] S11, a free radical precursor (diiodomethane CH2I2) is loaded into the bubbling bottle 25, and the first air pump 21 and the second air pump 15 are turned on, so that the fluorescence detection module is first in a low-pressure state to avoid affecting the normal measurement of the fluorescence signal; the first light source 3, the second light source 5, and the third light source 10 are turned on, so that the photolysis beam and the absorption beam of the photolysis precursor enter the reaction chamber 1, and the fluorescence detection beam enters the fluorescence detection module.

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

[0110] S13, the free radicals generated by the photolysis of the free radical precursor by the first light source 3 undergo a bimolecular reaction without the introduction of a reaction gas, and the concentration of the free radicals decays over time;

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

[0112]

[0113] Where X is the free radical concentration measured in real time; R L is the effective cavity length, that is, the ratio of the cavity length to the optical path length of a single absorption 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;

[0114] The concentration X of the free radical measured in real time is subjected to exponential fitting with the reaction time t. The exponential fitting formula is as follows:

[0115]

[0116] Among them, X t is the free radical concentration at time t, X0 is the free radical concentration at the initial time; ko1 is the free radical activity obtained by the first measurement method (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 radical itself is obtained by double exponential fitting. The double exponential fitting formula of the fluorescence signal is as follows:

[0118]

[0119] Among them, S radical is the real-time fluorescence signal, A0, A1 and a are all parameters of double exponential fitting; ko2 is the free radical activity obtained by the second measurement method (measurement method based on the fluorescence detection module).

[0120] S16, through multiple sets of experiments and exponential fitting, the free radical activity (ko) is obtained to verify the stability of the system. The free radical activities obtained by the two measurement methods can be mutually verified. If the difference in the free radical activity obtained by the two measurement methods does not exceed the set threshold, the free radical activity measurement result is reliable; otherwise, the free radical activity measurement result is unreliable.

[0121] Step 2: introducing a free radical precursor and reactants of different concentrations into the reaction chamber 1, measuring the activity of the free radicals in the bimolecular reaction, and obtaining 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 beam and the absorption beam of the photolysis precursor enter the reaction module, and the fluorescence detection beam enters the fluorescence detection module.

[0123] S22, through the industrial computer 26, open the first mass flow controller 2301 and the second mass flow controller 2302 for controlling the intake flow of the synthesis gas and the dilution gas 2401, open the third mass flow controller 2303 for controlling the flow of oxygen 2402, and open the fourth mass flow controller 2304 for controlling the reaction gas 2403.

[0124] S23, when the first light source 3 photodecomposes the precursor to generate free radicals, a bimolecular reaction occurs between the two when the reaction gas is introduced, and the concentration of the free radicals decays over time.

[0125] S24, the absorption detection module measures the change in the intensity of the absorption beam and calculates the ring-down time according to the Lambert-Beer law, inverts 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] Wherein, k1 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 attenuation signal of the fluorescence photons; the reaction activity of the free radical bimolecular reaction is obtained by double exponential fitting. The double exponential fitting formula of the fluorescence signal is as follows:

[0129]

[0130] Wherein, k2 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 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.

[0132] Among them, the free radical base activity ko1 obtained by the first method and the free radical activity k1 at different reactant concentrations are linearly fitted to obtain the bimolecular reaction rate constant v1 of the free radical; the free radical base activity ko2 obtained by the second method and the free radical activity k2 at different reactant concentrations are linearly fitted to obtain the bimolecular reaction rate constant v2 of the free radical. In this embodiment, the bimolecular reaction rate constants of free radicals obtained by the two measurement methods can be mutually verified, and the test results of one measurement method 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 free radicals and SO2 (reactant) has been fully verified, the reactant introduced in this embodiment is SO2 gas, and the measured bimolecular reaction rate constant v can be used to verify the accuracy of the present invention.

[0134] Experiments have shown that fluorescence detection provides more accurate results, eliminating interference from absorption spectral lines. Therefore, when measuring free radical background activity, the free radical background activity obtained using the fluorescence detection module (the second measurement method) is used as the benchmark. If the background results from absorption detection differ from those from fluorescence detection, the background value from the fluorescence detection method is used in subsequent absorption detection. This ensures background accuracy and eliminates interference from absorption detection.

[0135] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection 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 into 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 based on the detected signals; 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 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.

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) filled with 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 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 beam emitted by the first light source (3) is collimated by the beam expander (2), and after the diameter of the light spot is expanded, it is emitted into the reaction chamber (1) through the first window (101) at one end of the reaction chamber (1), and the free radical precursor in the reaction chamber (1) is photolyzed to produce free radicals. Subsequently, the photolysis beam is emitted through the second window (102) at the other end of the reaction chamber (1), and energy is monitored by the 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). It 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. It then passes through the second high-reflection mirror (104) at the other end of the reaction chamber (1) and is emitted. An 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 moments 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 a fluorescent signal after being excited by the laser; the second detector (17) is used to collect the fluorescent signal; 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 the rate constant of a free radical bimolecular reaction, characterized in that: A free radical bimolecular reaction rate constant measurement system according to any one of claims 1 to 5 is applicable, wherein the method is as follows: Step 1: Only the free radical precursor is introduced into the reaction chamber (1). 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: Perform linear fitting 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. The method for measuring a free radical bimolecular reaction rate constant according to claim 6, wherein: The first measurement method is as follows: The change in the absorption beam intensity 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 optical path length of a single absorption 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 subjected to exponential fitting with time t. 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 moment; k1 is the free radical activity obtained by the first measurement method.

8. The method for measuring the free radical bimolecular reaction rate constant according to claim 6, wherein: The second measurement method is as follows: The real-time fluorescence signal was fitted with a double exponential fitting with time t. The double exponential fitting formula is: Among them, S radical is the real-time fluorescence signal, A0, A1 and a are the parameters of the double exponential fitting; k2 is the free radical activity obtained by the second measurement method.

9. A computer program product, characterized in that The method comprises a computer program / instruction, which, when executed by a processor, implements a method for measuring a free radical bimolecular reaction rate constant according to any one of claims 6 to 8.

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