Infrared laser multiple-photon dissociation of CTCl3: Wavelength dependence, collisional effects, and tritium/deuterium isotope selectivity

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Abstract
Isotopically selective infrared multiple‐photon dissociation of CTCl3 in CDCl3 was investigated using a pulsed CO2 laser‐pumped NH3 laser in the 12 μm region. The wavelength dependence of CTCl3 MPD in the ν4 absorption band was studied and the observed MPD peak was found to be shifted ∼10 cm−1 to the red of the absorption peak at 835 cm−1, consistent with the anharmonicity of the CTCl3 ν4 mode. The CTCl3 dissociation probability per pulse was investigated under various experimental conditions, including laser energy, pulse duration, and CDCl3 and buffer gas pressure. A rate equation model was used to analyze the CTCl3 experiments assuming various multiple‐photon absorption and collisional relaxation mechanisms; this modeling effort was extended to a brief, more general, investigation of multiple‐photon absorption by molecules with prespecified dissociation probability profiles. Lower limit single step T/D enrichment factors in chloroform MPD exceeding 15 000 were achieved under optimized conditions of the above parameters. No evidence of any CDCl3 depletion or decomposition product was observed in irradiated 200 ppm CTCl3/CDCl3 mixtures. CDCl3 absorption measurements were made using an optically pumped NH3 laser, and the observed high fluence T/D optical selectivity was found to be sufficiently high for practical tritium recovery.