Enrichment of Silicon Isotopes with Infrared Free-Electron Laser Radiation

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 103; no. 21; pp. 4227 - 4232
• Main Authors: Lyman, John L, Newnam, Brian E, Noda, Tetsuji, Suzuki, Hiroshi
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27.05.1999
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp984699v

We have used the FELIX infrared free-electron laser (FEL) at the FOM Institute for Plasma Physics in The Netherlands to enrich silicon isotopes by multiple-photon dissociation of the molecule Si2F6. The absorption of infrared radiation induces the reaction Si2F6 → SiF4 + SiF2. Much of the SiF2 product further reacts to form additional SiF4. The Si2F6 molecule has absorption bands in the 10, 12, and 25 μm spectral regions. FEL-induced reactions occurred in all three regions. The reaction fraction was highest for the stronger band in the 10 μm region. Reactions in all three bands were isotopically selective. Irradiation in the 10 μm region at 952 cm-1 gave an isotopic selectivity of 5.6 for 30Si. For comparison, the published isotopic selectivity using a CO2 laser in the same spectral region is in excess of 17. We attribute the lower selectivity obtained with an FEL to its longer macropulse, its broader spectral width, and differences in experimental procedure. FEL irradiation in the region of the 12 μm band produced isotopic selectivities in excess of 20 for 30Si. Selective production of 28Si was high in the 25 μm region. We used changes in the infrared spectra of the irradiated samples for all analyses of reaction and isotope enrichment except for a single confirmation of enrichment with a mass spectrometer.