RU1783389C - Method of determination of concentration of oscillation-excites molecules of hydrogen - Google Patents

Abstract

The invention is based on the effect of nonequilibrium electron emission from the surface of solid samples discovered by the authors, stimulated by the transfer of energy of vibrational quanta from excited hydrogen molecules to electrons localized in a solid. The method includes the interaction of the molecules of the test gas and the molecules of the titrating substance and registration of the electrical signal caused by this interaction. A solid-state sensor sample a - AtaOa, previously irradiated with ultraviolet light (which ensures high sensitivity of the method) is introduced into the measuring cell as a titrating substance. A beam of vibrationally excited hydrogen molecules is directed to this solid-state sensor. In the course of measurements, the flow of vibrationally excited Hα molecules entering the measuring cell is modulated using a special damper. When the shutter is open, the total current of thermally stimulated and stimulated by a beam of vibrationally excited hydrogen (H2) molecules of electron emission is recorded, and when the shutter is closed, only the current of thermally stimulated electron emission from the photoexcited sample is recorded. 2 ill.

Description

The invention relates to measurement techniques, in particular to methods for determining the concentration of vibrationally excited molecules in gas mixtures, and can be used to measure the concentration of hydrogen molecules at high vibrational levels (v 2.

Known methods are: vacuum ultraviolet spectroscopy, vibroluminescence, Raman spectroscopy, isothermal calorimeter, EPR, used to register vibrationally excited diatomic homohedral molecules.

For example, when using the microcalorimetric method, the concentration of vibrationally excited molecules is judged by the measured signal from a thermocouple placed in the atmosphere of the test gas, which is proportional to the concentration of vibrationally excited molecules. Moreover, a qualitative determination of the desired concentration requires an appropriate graduation of the system.

Significant disadvantages of this method and the above methods are: the need for sophisticated hardware, lack of selectivity

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if the number of the excited vibrational level (microcalorimetric method), low sensitivity to small concentrations of vibrationally excited molecules.,

The technical solution closest to the invention is a vibro-aluminescent method for determining the content of vibrationally excited deuterium molecules. The method of vibroluminescence is based on the fact that the energy of the sixth rotational sublevel of the first vibrational level in D2 turns out to be exactly equal to the energy needed to stimulate the radiative transition in electronically excited nitrogen molecules No.e. This method is free from the main disadvantages inherent in the above methods.

In this method, the studied beam of vibrationally-excited deuterium molecules at the first vibrational level is sent to a measuring cell from a special source. Then, nitrogen enters the same volume. Nitrogen molecules play the role of a titrating substance and interact with the molecules of the studied beam. Since the energy of the sixth rotational sublevel of the first vibrational level of vibrationally excited deuterium molecules (D) is equal to the energy required for the radiative transition in electronically excited N2e nitrogen molecules, the nitrogen molecules are excited as a result of this interaction. The resulting luminescence of electronically excited nitrogen molecules is detected by known equipment. According to the intensity of the luminescent luminescence of excited nitrogen molecules, su

However, the known method described above has the following disadvantages. The technical solution implemented in it has selective sensitivity only to deuterium D2V molecules excited to the first vibrational level, and is not applicable for measuring the concentration of other vibrationally excited molecules, for example, hydrogen. Moreover, the use of electronically excited nitrogen molecules for chemiluminescent titration can introduce additional perturbations into the studied system, in particular, change the concentration of vibrationally excited molecules DЈ, which will be especially noticeable at low contents X in the test volume of these molecules

In addition, the known method has a low spatial resolution, which is a significant drawback in determining the distribution profiles of vibrationally excited molecules.

The purpose of the invention is to expand the class of analyzed gases and selectivity in relation to numbers of populated vibrational levels, increase the range of recorded concentrations of vibrationally excited molecules, and achieve high reliability and reproducibility of measurement results.

The claimed method is implemented as follows. To determine the concentration of vibrationally excited molecules, the molecules of the test gas and the molecules of the titrating substance are interacted and the electrical signal resulting from this interaction is recorded. A solid-state sensor is introduced into the measuring cell as a titrating substance: sample a — AlaOs, previously irradiated with ultraviolet light, and a beam of vibrationally excited hydrogen molecules is sent to it: during the measurements, the flow of vibrationally excited H2V molecules entering the measuring cell, using a special damper, and with the damper open, the total current r of thermostimulated and stimulated by a beam of vibrationally excited hydrogen molecules (H24 ) electron emission, and when the shutter is closed, only the current is recorded And the thermally stimulated emission of electrons of a photoexcited sample a - the desired concentration of vibrationally excited hydrogen molecules is judged by the relative increment of the current emis-12-I

these electrons Ј

formula H2 (v 2) - 8.0 10

in accordance with

cm

- for molecules at the second vibrational level, it is in accordance with the formula

H2 (v 5) 200

"2nd, ..- 3

cm

(at H2 (V 2) 4-105 H2 (v-5) - for molecules located at the fifth vibrational level.

The claimed method is based on the discovered effect of nonequilibrium electron emission from the surface of samples a-. Stimulated energy transfer of vibrational quanta from excited hydrogen molecules to electrons localized on traps in a solid. The same effect of nonequilibrium electron emission is observed from the surface of CaSCM-Eu, CaSO4-Mn samples.

A solid-state sensor made, for example, from a-. pre-irradiated with ultraviolet light from a mercury lamp in order to photo-excite the population of traps in the structure of a solid by electrons, and place them in a measuring cell. Vibrationally excited hydrogen (H2) molecules are obtained in a high-temperature source (T 1750 K) and sent to a solid-state sensor in a measuring cell. As a result of the interaction, the energy of vibrational quanta is transferred from excited hydrogen molecules to electrons localized on traps in a solid (sample a - A1203), and electron emission from the surface a - occurs. Emission current I is recorded by apparatus including a signal amplification unit. During the measurements, the flow of vibrationally excited Na molecules entering the measuring cell is modulated using a special damper. With the damper open, the equipment records the total electron emission current (la), which is thermally stimulated and stimulated by a beam of vibrationally excited hydrogen (H) molecules, directed to the solid-state sensor. When the shutter is closed, the access of hydrogen molecules to the measuring cell is stopped and only the current of thermally stimulated emission of electrons I (T 330 K) from the photo-excited sample a-A1aOz is recorded using the apparatus.

Based on the experiments, an analytical dependence is obtained that relates the relative increment of current measured by the apparatus

Gi

emissions | -j- from sample-s: - A120s s

the concentration of hydrogen molecules located at the second (V - 2) and fifth (v 5) vibrational level:

gbg

H2 () + 2, () - 200 ....

ABOUT)

According to expression (1), the desired concentration of vibrationally excited hydrogen molecules Hav, located at the fifth vibrational level, is determined:

H2 ()} 200

cm

5 10 15 20 25 0 5

0.

5

0

5

and when

H2 () 4-105 H2 (). - the concentration of hydrogen molecules located at the second vibrational level:

H2 () 8.0-107- -cm 3.

By selecting solid samples with different work function and the corresponding energy spectrum of electron traps and their concentration, one can determine in this way the concentration of molecules of various types located at different vibrationally excited levels.

The use of the claimed method for determining the concentrations of vibrationally excited hydrogen molecules provides, in comparison with existing methods, including the prototype, the following advantages.

The method has a selective sensitivity to H2V molecules. at a given vibrational level. In particular, the choice of sample a as the sensor ensures the determination of the concentration of molecules located at the fifth and second vibrational levels of excitation.

The preliminary population of electron traps by ultraviolet irradiation of a solid-state sensor with the light of a mercury lamp provides high sensitivity of the method (up to 104 Na (V-5) molecules).

The method provides simplicity and reliability of measurements, as well as good reproducibility of measurement results.

Figure 1 shows a diagram of a measuring apparatus for determining the concentration of vibrationally excited hydrogen molecules by the proposed method; figure 2 is a graph illustrating the proposed method.

The measuring installation comprises: measuring cell 1; a connecting flange 2, which is joined vacuum-tightly with a closed volume of the measuring cell, into which vibrationally excited hydrogen molecules enter, the second part of the flange having a slot 3, with the help of which an effusive molecular beam of Na1 is introduced into the cell; a damper (modulator) 4 bellows type, overlapping the beam; a sensitive element (sensor) 5 - a fine sample of a-A12Oz applied from an alcohol suspension to a substrate; electron emission registration system consisting of a secondary electron

a multiplier 6 and a standard system for amplifying and recording pulse signals 7; a system 8 for pre-exciting a solid-state sensor with ultraviolet light (mercury lamp); pumping system 9.

Example, Determination of concentrations of vibrationally excited hydrogen molecules located at the fifth vibrational level.

The source of vibrationally excited hydrogen molecules entering the measuring cell is made in the form of an alundum tube filled with hydrogen. The hydrogen in the tube is heated to 1750 K, the pressure At in the source is 2-3 Pa. The pressure in the measuring volume in the mode without a beam (the valve is closed) 1, Pa, and with a beam of vibrationally excited molecules Na (the valve is open) (8-10) Pa. The thermally equilibrium population of H2V, at T 1600 K and Pn 2.7 Pa, corresponds to the following concentrations of hydrogen molecules in the HvfKe source:

H2 () 7-6-1010CM 3;

H2 (v 5) 8.5-106CM 3.

These concentration values are determined based on the Boltzmann distribution.

On samples a-A1203 (sample temperature T 330 K), the electron emission current was measured in the measuring volume in the non-beam mode (Fig. 2, curve 1) and in the mode corresponding to the supply of the molecular beam into the cell with the sample (Fig. 2, curve 2). Thus, FIG. 2 shows the increment of the emission current h with an open beam H29 (V 5) relative to the emission current 11 with a closed beam (y-5). From the graph in figure 2 it can be obtained that the relative increment of the emission current in this case is equal to

t t2-H 175-100

$ M100

-0.75

(emission current values are taken, for example, for an exposure time of t 44 min). According to expression (1), the obtained value corresponds to the following concentrations of hydrogen molecules of the у sample:

H2 (a) 1200 150 cm 3;

H2 () 6-10 7CM 3.

These concentrations of H2 (V-5), H2 (y-2) in the measuring cell correspond to the following concentrations of H2 in the source tube (at T 1600 K, P 2.7 Pa):

H2 (v 5) 8.5-106CM 3 H2 (V 2) 7.6-1010CM 3.

These concentration values are determined based on the geometry of the experiment, which determines the course of the molecular beam in the measuring cell, taking into account the obtained value of Ј.

The relative error of the method is determined by the spread of the measurement results of the emission current and does not exceed 15%.

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Claims (1)

SUMMARY OF THE INVENTION A method for determining the concentration of vibrationally excited hydrogen molecules, including the interaction of gas molecules and molecules of a titrating substance and registration of an electrical signal resulting from this interaction, characterized in that, in order to expand the class of analyzed hydrogen molecules and selectivity with respect to numbers of populated vibrational levels, increasing the range recorded concentrations of vibrationally excited molecules, increasing the reliability and reproducibility of the result in measurements, a solid-state sensor is introduced into the measuring cell as a titrating substance - sample a - A120z, previously irradiated with ultraviolet light, and a beam of vibrationally excited hydrogen molecules is sent to it, while the measurement process, the flow of vibrationally excited H2 molecules is modulated ° entering the measuring cell through the damper, and when the damper is open, the total current 1 of thermostimulated and stimulated by a beam of vibrationally excited hydrogen molecules is recorded ( ) Emission of electrons, and when the valve is closed and thermally stimulated current register emission of electrons from the photoexcited sample ss-A12Oz. and the desired concentration of vibrationally excited hydrogen molecules is judged by the relative increment of the emission current of electrons Ј -j- in accordance with the formula H2 () 8.0-10 7 2 il, cm 3 - for molecules located at the second vibrational level, and in accordance with the formula . with. 3 1 H2 () 200 cm (at H2 (v - 2) 4 105 tH2 (V 5)) - for molecules at the fifth vibrational level. I EKGroU etu s. about tfQO300 100iOO Champions League Fng. 1  -fvUMJl.