The multiphoton absorption and decomposition of fluoroform-d: Laser isotope separation of deuterium

Abstract

Multiphoton absorption (MPA) studies of fluoroform-d, a molecule of interest for potential laser based hydrogen isotope separation processes, are reported for CDF3 pressures 0.2–1.3 kPa, and for a variety of 10 μm CO2 laser lines with pulse widths of 2 or 6 ns and fluences within the range 10−3–70 J/cm2. Unlike SF6, no red shift of the MPA spectrum relative to the small signal spectrum was observed at high fluence. Selective multiphoton decomposition (MPD) experiments using the 10R(26) line, 6 ns pulse to excite the CDF3 component in natural-abundance CHF3 (∼ 150 ppm D/H) at a pressure of 13.3 kPa resulted in the recovery of water enriched up to 30% in deuterium—a measured isotope enrichment of ⩾2000 fold. This demonstrates that a product, highly enriched in deuterium, can be recovered from the selective MPD of fluoroform.

Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed 13CO2 laser

“…The observed peak of the large signal spectrum is shifted to lower energy by 2 5 cm-' from that of the small signal spectrum. This is a larger shift than was observed for CDF, (10) and suggests that anharmonicity bottle-necking (34, 35) is more severe for CDC1, than CDF, (33, 36).…”

“…This probably indicates that the small anharmonicity bottle-necking for the pumped mode of CDF, (9,10,41) compensates for the more slowly rising p v l~ versus excitation energy for CDF, compared to CDC1,. Selective MPD measured elsewhere (23) indicates that D/H selectivity is smaller for CDCI, (with excitation at 11 pm) than for CDF,.…”

“…[lo] DCI + Hz0 = HDO + HCI A similar exchange was observed for selective MPD of fluoroform (10). Attempts to study selective MPD of CHC1,/CDCl3 mixtures by observing FTIR depletion of CHC1, and CDC1, peaks was also unsuccessful since product FTIR peaks interfere with the CDC1, peaks in the spectrum.…”

“…The absorption cross sections u(@) were corrected for the Gaussian distribution of the beam and for changes in fluence along the beam as previously described (9,10). The values of u(@) were then found to fit well to the empirical form of (4, 9, 10, 29) of eq.…”

“…Of these, fluoroform is currently the one most promising (6)(7)(8)(9)(10)(11)(12)(13)(14) and may also be suitable for tritium recovery (1 5-18). However, there are two major obstacles to the use of fluoroform in a heavy water process: ( a ) efficient MPD of fluoroform requires fluences in excess of 20 J/cm2, which, combined with the need to use short pulses (9) (AT .= 1-2 ns) leads to laserinduced damage of windows which complicate the design of the photolysis cell and (b) exchange of fluoroform with water or natural gas is too slow for a practical exchange step without ' AECL Contribution Number 8869 the use of a catalyst ( 1 1).…”