Multiphoton decomposition of 10BCl 3 and 11BCl 3 by CO 2 TEA laser

Abstract

The infrared multiphoton decomposition of enriched 10BCl 3, enriched 11BCl 3, and their mixtures has been studied in the presence of oxygen. The CO 2 TEA laser used was tuned to the P(20) line of the 10.6 μm band (944.2 cm −1), which is in resonance with the v 3 mode of 11BCl 3. The dependences of the apparent decomposition rate and luminescence intensity on the laser fluence indicate the initial decomposition of BCl 3 followed by radical scavenging of oxygen. The ratio of the apparent decomposition rates obtained separately with 98% 10BCl 3 and 97% 11BCl 3 under the same experiment conditions was found to be 4.7 ± 1.3. On the other hand, the corresponding ratio obtained with natural BCl 3 was about 1.3. The large decrease should be due to the V—V energy transfer between highly excited 11BCl 3 and unexcited 10BCl 3 molecules. The dependences of apparent decomposition rates and isotope selectivity were examined as functions of 10BCl 3 or 11BCl 3 pressure. The isotope selectivity depends on only the pressure of 11BCl 3 which absorbs laser radiation, whereas it remains constant over 10BCl 3 pressure. The observed results can be explained consistently by the mechanism involving the two kinds of excited molecules, BCl + 3 and BCl * 3, where one has a lifetime of a few microseconds and the other decomposes instantaneously.