JPH0513685B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a working material used in laser isotope separation for separating isotopes of Si, and a method for laser isotope separation of Si using this working material. (Prior Art) The absorption spectrum of molecules in the infrared region with wave numbers of 10 ² to ^{10 3} cm ^-1 corresponds to changes in the vibrational state of the molecule and often shows significant isotopic effects. Therefore, it is possible to focus on molecules containing a specific isotope and selectively excite the molecules by irradiating them with light near the wave number where absorption is large, inducing a chemical reaction and leading to separation. If a normal molecule absorbs only one photon of light in the above-mentioned region, the energy is insufficient and no chemical reaction occurs. However, when exposed to powerful infrared laser light, the molecules absorb up to several dozen photons and break down. This kind of decomposition is called infrared multiphoton dissociation. Natural Si isotopes with masses 28, 29, and 30 exist in the ratio of [ ²⁸ Si]:[ ²⁹ Si]:[ ³⁰ Si]=92.23:4.67:3.10. Until now, Si has been analyzed by infrared multiphoton dissociation
The isotope separation of _SiF4 has been little studied, and only the enrichment of ^29SiF4 and _30SiF4 has been reported in a carbon dioxide laser ^experiment using _SiF4 as the working material (JLLyman
and SDRockwocd；J.Appl.Phys., Vol.47, No.
2, P.595-601, (1976)). However, the selectivity of enrichment in this experiment is extremely low, and the enrichment of ²⁹ Si and ³⁰ Si increases only to about 5%, so it is difficult to recognize the practical significance. On the other hand, the present inventors previously discovered that SiaXbHc (2≦a
≦3, 0≦b≦2a+2, 2a+2=b+c, X is the same or different halogen atom) is the oscillation region of the infrared laser
It has absorption corresponding to molecular vibrations in the range 930 to 1060 cm ^-1 , and when irradiated with pulsed infrared laser light in the vicinity, it causes infrared multiphoton dissociation extremely efficiently.
He discovered that it decomposed into lower-order silanes and filed a patent application (see Japanese Patent Application No. 21577/1983). (Object of the Invention) The object of the present invention is to provide a laser isotope separation method and working material for efficiently separating Si isotopes, which were obtained as a result of intensive research by the present inventors after the application was filed. It is in. (Structure of the invention) The present invention uses SiFnX _4-o (X is H,
Using a fluoromonosilane compound represented by any one of Cl, Br, I, where 1≦n≦3) or SiFnR _4-o (R is an alkyl group or its halogen derivative, but 1≦n≦3), By irradiating a fluoromonosilane compound with an infrared laser
Isotopes of Si are separated. The fluoromonosilane compounds as working substances include SiF ₃ H, SiF ₃ Cl, SiF ₃ Br, SiF ₂ H ₂ ,
Examples include SiFCl ₃ , SiF ₃ CH ₂ , SiF ₃ CF ₂ and SiF ₂ (CH ₃ ) _2. Examples of infrared lasers include carbon dioxide laser, HF laser, and lasers that convert wavelength into infrared light (for example, hydrogen Raman laser). laser)
etc. are included. Among these, carbon dioxide laser is particularly preferred because of its good wavelength matching with molecular vibration and high laser beam intensity. The above fluoromonosilane compounds are all Si
It has a strong absorption band corresponding to the stretching vibration of the -F bond in the infrared laser oscillation region. When irradiated with an infrared laser oscillation line near the absorption band of each compound, either as parallel light or lightly focused with a lens, each compound is easily dissociated. The product obtained in this way is separated from the unreacted parent compound by low-temperature distillation or gas chromatography, and the isotope ratio in Si is measured using a mass spectrometer ^. It can be seen that ³⁰ Si is concentrated and ²⁸ Si is concentrated in the unreacted parent compound. In addition,
It is appropriate that the irradiation wavenumber be 20 to 50 cm ^-1 lower than the peak of the infrared absorption band of the parent compound, and if the wavenumber is lower than this, the yield of the product will drop significantly. The lower the irradiation temperature, the better the selectivity, and the preferable pressure is around 1 Torr; if the sample pressure is raised too much, the selectivity will decrease. (Effects of the Invention) According to the present invention, ²⁹ Si and ³⁰ Si can be efficiently separated by irradiating the work material made of the fluoromonosilane compound with an infrared laser to separate Si isotopes. It is effective in the production of Si isotopes, which are in increasing demand in research on pharmaceuticals and agrochemicals, and the development of electronic materials. Furthermore, compared to the mass spectrometry method currently used for Si isotope separation, the manufacturing cost of this laser method is extremely reduced, and it is possible to provide Si isotopes in large quantities at low cost. (Example) The present invention will be explained below using examples. The laser device used was Lumnics model 103-2.
A CO ₂ TEA laser device produces a mixture of He and CO ₂ gas,
Alternatively, a gas mixture of He, CO ₂ and N ₂ was used to generate laser oscillation. In the case of the former gas mixture, the time width of the laser pulse is short, but the energy of the pulse is small. In the case of the latter gas mixture, the laser pulse oscillates over a long time width, increasing the energy of the pulse several times or more. FIG. 1 is a schematic diagram of the experimental setup used to carry out the invention. The pulsed laser beam 2 oscillated by the CO ₂ TEA laser device 1 and emitted to the outside passes through a circular iris 3 with a diameter of 1.0 or 1.6 cm, and then remains as a parallel beam or remains as a parallel beam.
After being focused by the BaF ₂ lens 4, the light is guided into the reaction vessel 5. The infrared absorption spectrum of the sample before and after laser irradiation is measured by an infrared spectrophotometer 6. After the sample has been irradiated with laser light, the product SiF ₄ is once separated in a low-temperature distillation device 7, and then it is introduced directly into a mass spectrometer 8 and a gas chromatograph 9. <First Example> In this example, SiF ₃ CH ₃ was used as the working material. FIG. 2a is a diagram showing the infrared absorption spectrum of this working material before irradiation with laser light.
The pressure of the sample was 1 ^Torr ; Si
-A strong absorption band due to the stretching vibration of F is observed. Next, this sample was irradiated with a pulsed laser beam of the P(22) line (942.38 cm ^-1 ) in the 10.6μ band, which was oscillated using a gas mixture of He, CO ₂ and N _{2 ,} as parallel light. Laser light fluence is 0.62J
It was warm at cm ^-2 . The infrared absorption spectrum measured after irradiation up to 5000 pulses is shown in Figure 2b.
The newly appeared absorption shoulder near 1020 cm ^-1 is due to SiF ₄ . The irradiated sample is introduced into a gas chromatograph and mass spectrometer, and the product
We measured the isotope ratios of ²⁸ Si, ²⁹ Si, and ³⁰ Si in _SiF4 , but
The values are fragment ions ²⁸ SiF ₃ ⁺ , ²⁹ SiF ₃ ⁺ ,
³⁰ Based on the ionic strength ratio of SiF ₃ ⁺ . The results are shown in Table 1. ²⁹ Si and ³⁰ Si are each 12.42% in SiF ₄ ,
Concentrated to 9.94%.

[Table] In addition, the same experiment was conducted using the same SiF ₃ CH ₃ as the working material and changing the laser light irradiation conditions. A pulsed laser beam (10.6 μ band, P(22) line) of 942.38 cm ^-1 oscillated using a gas mixture of He and CO ₂ was used as the laser beam. This laser light was attenuated through a polyethylene film, then focused by a lens with a focal length of 40 cm, and then introduced into a reaction vessel filled with 1 Torr of SiF ₃ CH ₃ . The laser fluence at the focus was 5.6 Jcm ^-2 . The infrared absorption spectrum after irradiation up to 2000 pulses is shown in Figure 2c. When the sample was introduced into a gas chromatograph and a mass spectrometer and measured, it was found that ²⁹ Si was concentrated in SiF ₄ to 8.87% and ³⁰ Si was concentrated to 11.19%, as shown in Table 2.

[Table] <Second Example> In this example, SiF ₃ Br was used as the working substance. A pulsed laser beam (10.6 μ band R(14) line) of 971.93 cm _-1 oscillated using a gas mixture of He, CO ₂ and N ₂ was applied to a reaction vessel filled with 1 Torr of SiF ₃ Br. It was introduced as parallel light. The fluence of the laser light was 0.59 Jcm ^-2 and the number of irradiation pulses was 500. Figures 4a and 4b are graphs showing infrared absorption spectra before and after laser irradiation, respectively. It is clear from these graphs that SiF ₄ was generated by laser light irradiation. Next, the sample in the reaction container after irradiation with laser light was introduced into a gas chromatograph and a mass spectrometer. The gas chromatogram obtained at that time is shown in FIG. SiF ₄ and
The SiF ₃ Br peak appears. Table 3 shows the results of mass spectrometry for the obtained _SiF4 .
It can be seen that ²⁹ Si and ³⁰ Si are concentrated to 6.35% and 7.81%, respectively.

【table】 [Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the experimental equipment used to carry out the present invention, and Figs. 2a to 2c show infrared absorption before laser beam irradiation when SiF ₃ CH ₃ is used as the working material. Diagram showing the spectrum, 3rd
Figures a and 3b show the infrared absorption spectra before laser light irradiation when SiF ₃ Br is used as the working material, and Figure 4 shows the infrared absorption spectrum when SiF 3 Br is used as the working material.
FIG. 3 is a diagram showing a gas chromatogram after laser light irradiation when SiF ₃ Br is used. 1... Laser device, 2... Laser light, 3...
...Iris, 4...Lens, 5...Reaction vessel, 6
...Infrared spectrophotometer, 7...Cryogenic distillation device, 8...
...Mass spectrometer, 9...Gas chromatography.

Claims (1)

[Claims] 1 SiFnX _4-o (X is H, Cl, Br, I, 1≦n≦3) or SiFnR _4-o (R is an alkyl group or its halogen derivative, 1 ≦n≦
3) A working material for laser isotope separation of Si, which is a fluoromonosilane compound represented by: 2. The working material according to claim 1, wherein the fluoromonosilane compound is a trifluoromonosilane compound. 3 The trifluoromonosilane compound is
The working material according to claim 2, characterized in that it is SiF ₃ Br. 4 The trifluoromonosilane compound is
The working material according to claim 2, characterized in that it is SiF ₃ CH ₃ . 5 SiFnX _4-o (X is H, Cl, Br, I, 1≦n≦3) or SiFnR _4-o (R is an alkyl group or its halogen derivative, 1≦n≦
3) A laser isotope separation method that irradiates the fluoromonosilane compound represented by (3) with an infrared laser to separate Si isotopes. 6. The laser isotope separation method according to claim 5, wherein the infrared laser is a carbon dioxide laser.