JPH0256133B2 - - 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 has isotopes with mass numbers 28, 29, and 30 [ ²⁸ Si]: [ ²⁹ Si]: [ ³⁰ Si] = 92.23: 4.67: 3.10
It exists in the ratio of Until now, Si isotope separation by infrared multiphoton dissociation has hardly been studied, but enrichment of ²⁹ SiF ₄ and ³⁰ SiF ₄ was reported in an experiment using a carbon dioxide laser using only SiF ₄ as the working material. (JLLyman
and SDRockwocd；J.Appl.Phys., Vol.47, No.
2, P.595-601, (1976)). (Problem to be solved by the invention) However, the selectivity of enrichment in this experiment was extremely low, and the concentrations of ²⁹ Si and ³⁰ Si increased only to about 5%, so the practical significance is recognized. hard. Today, demand for Si isotopes is increasing in pharmaceutical and agrochemical research and the development of electronic materials, and the development of more efficient separation methods is desired. An object of the present invention is to provide a laser isotope separation method and working material that efficiently separates Si isotopes. (Means for solving the problem) The above problem is SiaXbHc (2≦a≦3, 0≦b≦
This problem is essentially solved by using a polysilane compound represented by 2a+2, 2a+2=b+c, where X is the same or different halogen atom, as a working substance. By irradiating this polysilane compound with an infrared laser, Si isotopes are separated. The _SiaXbHc polysilane compounds as working _substances include _{Si2F6 , Si3F8 , Si2F3Cl} , _Si2F5Br ,
Examples include Si ₂ F ₅ H and Si ₂ FH ₅ , and infrared lasers include carbon dioxide lasers, HF lasers, and lasers whose wavelengths are converted into infrared rays (for example, hydrogen Raman lasers). Among these, carbon dioxide laser is particularly preferred because of its good wavelength matching with molecular vibration and high laser beam intensity. (Function) Ordinary infrared multiphoton dissociation of molecules is induced only in a region of high energy density near the focal point obtained by focusing laser light, and it is difficult to obtain a high yield. Polysilane compounds decompose efficiently even when irradiated with laser pulses of very low energy density. This is thought to be because the bonds between Si atoms are extremely weak. The SiaXbHc polysilane compound has absorption corresponding to molecular vibration in the infrared laser oscillation region of 930 to 1060 cm ^-1 , and when irradiated with infrared laser pulse light in this area, it can perform infrared multiphoton dissociation extremely efficiently. and decomposes into lower silanes. In addition to ²⁸ Si, ²⁹ Si and ³⁰ Si exist in natural Si compounds in a certain proportion, and the infrared absorption peak of ²⁹ Si is on the lower wavenumber side than the absorption peak of ²⁸ USi.
It is known that the absorption peak of ³⁰ Si is located on the lower wavenumber side. Therefore, natural said
When a SiaXbHc polysilane compound is irradiated with a laser pulse of an appropriate wave number, molecules containing each isotope are selectively excited reflecting the difference in absorption spectra, and in the subsequent decomposition reaction, ²⁹ Si or
³⁰ Si is concentrated in lower order silanes. (Example) The present invention will be described below with reference to Examples. FIG. 1 is a schematic diagram of the experimental apparatus used to carry out the present invention. This experimental apparatus is configured as follows. Carbon dioxide TEA laser 1
uses a gas mixture of helium and carbon dioxide as the laser medium. This carbon dioxide TEA laser 1
The pulsed laser beam 2 generated from is 1.5cm in diameter.
After passing through the iris 3, the light is projected into the reaction vessel 4, and the working substance filled inside is irradiated.
The reaction container 4 is a cylindrical container with a length of 1 m, and is installed inside a constant temperature bath 5 and maintained at a predetermined temperature. The energy density of the laser beam is measured by a power meter 6 installed at the tip of the reaction vessel 4. The yield of the reaction decomposition product lower-order silane and the concentration of ²⁹ Si or ³⁰ Si concentrated therein vary in a complex manner depending on the laser wave number, energy density, irradiation temperature, and sample pressure, but depending on the choice of separation. The selectivity generally improves as the energy density, irradiation temperature, and sample pressure are lowered, and the influence of laser wave number on selectivity often reflects differences in absorption spectra. Next, one embodiment according to the present invention will be described. Using the apparatus shown in Figure 1, using 2 Torr Si ₂ F ₆ kept at room temperature as the working material, and using a pulsed laser beam with a wave number of 952.88 cm ^-1 and an energy density of 0.32 Jcm ^-2 as the laser beam, The work material was irradiated with this laser light as parallel light. The number of irradiation pulses is
It was 500. After irradiation, the sample was condensed and collected in a trap cooled to liquid nitrogen temperature, followed by cryogenic distillation to separate the product SiF ₄ . FIG. 2 shows the infrared absorption spectrum of SiF ₄ thus obtained. The absorption peak of ²⁸ _SiF4 is
It is located at 1031.8 cm ^-1 , but another absorption peak is observed on the lower wavenumber side of 18 cm ^-1 , which corresponds to ³⁰ SiF ₄ . That is, from this infrared absorption spectrum,
It can be seen that ³⁰ Si is concentrated in the product at a high concentration. The following table summarizes the mass spectrometry results of the product _SiF4 . ²⁸ SiF ₄ ⁺ resulting from SiF ₄ and
The intensity of the ion signal of ²⁸ SiF ₃₊ is set as 100 ^.
The intensity of the ion signals of ²⁹ SiF ₄ ⁺ , ³⁰ SiF ₄ ^{+, 29} SiF ₃ ⁺ , ³⁰ SiF ₃ ⁺ and the results obtained
The abundance ratios of ²⁸ Si, ²⁹ Si and ³⁰ Si are shown.

[Table] From the above results, the isotope ratio in the product SiF ₄ is [
²⁸ Si]: [ ²⁹ Si]: [ ³⁰ Si] = 50.2: 13.1: 36.7, and compared to the natural isotope ratio, ²⁹ Si is 2.8 times, ³⁰ Si
It can be seen that it is 11.8 times more concentrated. Further, a product SiF ₄ was obtained by the same operation as in the above example except that Si ₃ F ₈ was used as the working material. From the results of mass spectrometry, the isotope ratio of this substance is [ ²⁸ Si]: [ ²⁹ Si]: [ ³⁰ Si] = 75.3: 6.6: 18.1, which shows that it is clearly more concentrated than the natural isotope ratio. . Furthermore, when similar experiments were performed on other SiaXbHc polysilane compounds, it was possible to efficiently separate Si isotopes. (Effects of the Invention) As described above, the present invention irradiates a working material made of the SiaXbHc polysilane compound with an infrared laser to separate Si isotopes.
²⁹ Si and ³⁰ Si can be efficiently separated.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the experimental equipment used to carry out the invention, Figure 2 is a working material.
1 is an infrared absorption spectrum of the product SiF ₄ obtained using Si ₂ F ₆ . 1... Carbon dioxide laser, 2... Laser light,
3...Iris, 4...Reaction container, 5...Thermostat, 6...Power meter.

Claims (1)

[Claims] 1 SiaXbHc (2≦a≦3, 0≦b≦2a+2, 2a
A working material for laser isotope separation of Si, characterized in that it is a polysilane compound represented by +2=b+c and X is the same or different halogen atom. 2. The working material according to claim 1, wherein the polysilane compound is a halogenated disilane or trisilane having a fluorine atom. 3. The working material according to claim 2, wherein the halogenated disilane having a fluorine atom is Si ₂ F ₆ . 4. The working material according to claim 2, wherein the halogenated trisilane having a fluorine atom is Si ₃ F ₈ . 5 SiaXbHc (2≦a≦3, 0≦b≦2a+2, 2a
A laser isotope separation method in which a polysilane compound represented by +2=b+c (where X is the same or different halogen atom) is irradiated 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.