Hydroxyl radical magnetic rotation spectrum reference pool

Abstract

The invention discloses a hydroxyl radical magnetic rotation spectrum reference cell, which relates to the technical field of laser spectrum measurement of hydroxyl radical concentration, and comprises a cavity, a magnet and an electrode, the cavity comprises a flowing pipe for introducing water vapor; the magnet comprises a magnet framework and a winding wire wound on the magnet framework; the magnet sleeves the middle section of the cavity; the electrode comprises a first electrode ring and a second electrode ring which are located in the flow pipe and coaxially installed at the two ends of the flow pipe. And the detection light beam passes through the centers of the flow tube, the first electrode ring and the second electrode ring. The reference pool device is simple, high-concentration OH can be stably generated under the Doppler absorption line type condition of OH, the signal-to-noise ratio of OH absorption spectrum signals is high, and detection of laser wavelength locking is facilitated. The implementation mechanism of the invention is as follows: water molecules are electrolyzed to form OH free radicals in the alternating current discharge process of low-pressure water vapor;

Description

Technical Field

[0001] This invention relates to the field of laser spectroscopy measurement technology for hydroxyl radical concentration, and in particular to a hydroxyl radical magnetic rotation spectroscopy reference cell. Background Technology

[0002] The total reactivity of hydroxyl radicals (OH) is a key atmospheric photochemical parameter, characterizing the total amount of all trace components in the atmosphere that can be oxidized from an oxidizing perspective, and directly reflecting the degree of air pollution. Time-resolved laser-flash photolysis-magnetic rotation spectrometry is the only laser absorption spectroscopic method for measuring the total reactivity of OH (Time-resolved laser-flash photolysis Faraday rotation spectrometer: a new tool for total OH reactivity measurement and free radical kinetics research, Analytical Chemistry, 2020, 92, 4334-4339; Development of a portable laser-flash photolysis Faraday rotation spectrometer for measuring atmospheric total OH reactivity, Atmospheric Measurement Techniques, 2025, 18, 1243-1256). In this method, the emission wavelength of the probe laser is tuned to the OH absorption peak. By recording the concentration decay process caused by the reaction of OH generated by the flash with atmospheric components in a magnetic field, a time-resolved magnetic rotation spectral decay signal is obtained. Fitting this signal yields the total OH reactivity.

[0003] During long-term continuous operation of a laser flash photolysis-magnetic rotation spectroscopy device, due to the inherent characteristics of the laser, the emitted wavelength, which is fixed at the OH absorption peak by current bias, will drift, leading to a decrease in the measurement signal-to-noise ratio or even signal loss, severely affecting the observation quality. Chinese invention patent CN109856065A, a hydroxyl radical reactivity measurement device, discloses a laser flash photolysis-magnetic rotation spectroscopy device in which the frequency of the probe laser is locked to a reference cell, achieving long-term stability of the laser emitted wavelength. However, this patent does not disclose information about the reference cell structure. Utilizing the high concentration of molecular absorption within the reference cell to stabilize the laser wavelength is a classic approach in laser spectroscopy detection. Since there are no standard samples for OH and its lifetime is less than 1 second, it cannot be sealed and stored in a reference cell, making the fabrication of an OH reference cell extremely challenging. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a hydroxyl radical magnetic rotation spectral reference cell. The device is simple and can stably generate high concentrations of OH under the Doppler absorption line shape of OH. The OH absorption spectral signal has a high signal-to-noise ratio, which is beneficial for detection laser wavelength locking.

[0005] To achieve the above objectives, the present invention adopts the following technical solution, including:

[0006] A hydroxyl radical magnetic rotation spectroscopy reference cell includes a cavity, a magnet, and electrodes;

[0007] The cavity includes: a flow tube, windows installed at both ends of the flow tube, and air inlets and exhaust ports opened at both ends of the flow tube.

[0008] The magnet includes: a magnet frame and a winding wound around the magnet frame; the magnet is sleeved on the outer side of the middle section of the cavity;

[0009] The electrode includes: a first electrode ring and a second electrode ring located inside the flow tube and coaxially mounted at both ends of the flow tube;

[0010] The probe beam passes through the center of the flow tube, the first electrode ring, and the second electrode ring.

[0011] Preferably, the electrode operates in a high-voltage AC discharge mode.

[0012] Preferably, the electrode's power supply voltage is greater than 1kV and the AC frequency is greater than 1kHz.

[0013] Preferably, the magnet further includes: a coolant inlet and a coolant outlet disposed at both ends of the magnet frame, and a cooling interlayer formed by the magnet frame and the flow tube.

[0014] Preferably, the flow tube is made of quartz and the working air pressure is less than 20 mbar.

[0015] Preferably, the magnet skeleton is made of non-metallic material and operates in DC or AC mode.

[0016] Preferably, the sample in the reference cell is flowing water vapor with a flow rate of less than 1 L / min.

[0017] Preferably, the windows at both ends of the flow tube are calcium fluoride wedge-shaped windows.

[0018] Preferably, the detection beam is a tunable beam in the mid-infrared 2.8μm band.

[0019] Preferably, the electrode further includes: a first terminal and a second terminal electrically connected to the first electrode ring and the second electrode ring respectively; the first electrode ring and the first terminal are electrically connected to form an integral unit, and the second electrode ring and the second terminal are electrically connected to form an integral unit.

[0020] The advantages of this invention are:

[0021] (1) The reference cell device of the present invention is simple and can stably generate high concentration of OH under the Doppler absorption line condition of OH. The signal-to-noise ratio of OH absorption spectrum signal is high, which is beneficial for detection laser wavelength locking.

[0022] (2) The implementation mechanism of the present invention is: during the alternating discharge process of low-pressure water vapor, water molecules are electrolyzed to form OH free radicals. Attached Figure Description

[0023] Figure 1 This is a structural diagram of a hydroxyl radical magnetic rotation spectroscopy reference cell according to the present invention.

[0024] Figure 2 This is a high signal-to-noise ratio OH absorption spectrum obtained from actual experiments of this invention.

[0025] Explanation of reference numerals in the attached figures:

[0026] Cavity 1, magnet 2, electrode 3, flow tube 11, first calcium fluoride wedge window 12, second calcium fluoride wedge window 13, air inlet 14, air outlet 15, coolant inlet 21, coolant outlet 22, magnet frame 23, winding 24, first electrode ring 31, first terminal block 32, second electrode ring 33, and second terminal block 34. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Depend on Figure 1 As shown, a hydroxyl radical magnetic rotation spectroscopy reference cell of the present invention includes a cavity 1, a magnet 2, an electrode 3 and a probe beam;

[0029] The cavity 1 includes: a quartz flow tube 11 with a length of 70cm and an outer diameter of 1 inch; a 1-inch first calcium fluoride wedge window 12 and a 1-inch second calcium fluoride wedge window 13 that are glued and sealed at both ends of the flow tube 11; and an air inlet 14 and an air outlet 15 with an outer diameter of 6mm at both ends of the flow tube 11.

[0030] The magnet 2 includes: an epoxy glass magnet frame 23, a coolant inlet 21 and a coolant outlet 22 with an outer diameter of 12 mm at both ends of the magnet frame 23, and a 1 mm diameter enameled copper wire 24 wound around the magnet frame 23.

[0031] The magnet frame 23 is sleeved on the outside of the middle section of the flow tube 11, and a cooling jacket 25 with a thickness of 1 cm is formed between the magnet frame 23 and the flow tube 11, which is used to simultaneously control the temperature of the magnet 2 and the flow tube 11 by the coolant.

[0032] The electrode 3 includes: a first electrode ring 31, a first terminal block 32, a second electrode ring 33, and a second terminal block 34; the first electrode ring 31 and the first terminal block 32 are electrically connected to form a whole, and the second electrode ring 33 and the second terminal block 34 are electrically connected to form a whole; the first electrode ring 31 and the second electrode ring 33 are respectively installed at both ends of the flow tube 11 and are coaxially mounted; the first electrode ring 31 and the second electrode ring 33 are made of copper, with an outer diameter of 25 mm and an inner diameter of 15 mm; the first terminal block 32 and the second terminal block 34 are vacuum-sealed with the flow tube 11.

[0033] The detection beam is a tunable beam in the mid-infrared 2.8μm band with a diameter of less than 10mm, passing through the center of the flow tube 11, the first electrode ring 31, and the second electrode ring 33.

[0034] The electrode 3 operates in a high-voltage AC discharge mode.

[0035] The working pressure of the cavity 1 (flow tube 11) is less than 20 mbar, and the typical working air pressure is 10 mbar.

[0036] The magnet 2 can operate in DC mode with a typical magnetic field strength of 200 Gauss.

[0037] The supply voltage of electrode 3 is greater than 1kV and the AC frequency is greater than 1kHz, with typical values ​​of 1.5kV and 10kHz.

[0038] The sample in the reference cell is flowing water vapor, that is, flowing water vapor is introduced into the flow tube 11 at a flow rate of less than 1 L / min, with a typical value of 100 mL / min.

[0039] The mechanism of this invention is as follows: during the alternating discharge process of low-pressure water vapor, water molecules are electrolyzed to form OH free radicals.

[0040] Based on the typical values ​​in the above embodiments, the obtained OH absorption spectrum signal is as follows: Figure 2As shown, the OH absorption signal is stable and the spectral signal-to-noise ratio is high. The measured absorption peak for OH is at 3568.52 cm⁻¹. -1 The Q(1.5) line at the point yielded a stable OH concentration of 78 ppmv and a spectral signal-to-noise ratio of 52, which fully demonstrates the practical feasibility of the present invention.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydroxyl radical magnetic rotation spectral reference cell, characterized in that, Includes cavity (1), magnet (2), and electrode (3); The cavity (1) includes: a flow tube (11), windows installed at both ends of the flow tube (11), an air inlet (14) and an air outlet (15) opened at both ends of the flow tube (11); The magnet (2) includes: a magnet frame (23) and a winding (24) wound around the magnet frame (23); the magnet (2) is fitted outside the middle section of the cavity (1); The electrode (3) includes: a first electrode ring (31) and a second electrode ring (33) located inside the flow tube (11) and coaxially mounted at both ends of the flow tube (11); The probe beam passes through the center of the flow tube (11), the first electrode ring (31), and the second electrode ring (33).

2. The hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The electrode (3) operates in high-voltage AC discharge mode.

3. The hydroxyl radical magnetic rotation spectral reference cell according to claim 2, characterized in that, The power supply voltage of electrode (3) is greater than 1kV and the AC frequency is greater than 1kHz.

4. The hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The magnet (2) further includes: a coolant inlet (21) and a coolant outlet (22) disposed at both ends of the magnet frame (23), and a cooling jacket (25) formed by the magnet frame (24) and the flow tube (11).

5. The hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The flow tube (11) is made of quartz and has a working air pressure of less than 20 mbar.

6. The hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The magnet frame (23) is made of non-metallic material, and the winding (24) operates in DC mode or AC mode.

7. The hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The sample in the reference cell was flowing water vapor at a flow rate of less than 1 L / min.

8. A hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The windows at both ends of the flow tube (11) are calcium fluoride wedge-shaped windows.

9. A hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The detection beam is a tunable beam in the mid-infrared 2.8μm band.

10. A hydroxyl radical magnetic rotation spectral reference cell according to claim 1, characterized in that, The electrode (3) further includes a first terminal (32) and a second terminal (34) that are electrically connected to the first electrode ring (31) and the second electrode ring (33) respectively; the first electrode ring (31) and the first terminal (32) are electrically connected to form an integral whole, and the second electrode ring (33) and the second terminal (34) are electrically connected to form an integral whole.

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