Isotope-selective IR multiphoton dissociation of CHClF2 in the presence of NO2

Addition of NO2 to the CHClF2/He mixture irradiated by a Q-switched CO2 laser leads to oxidation of the dissociation product according to the reaction: CF2 + NO2 --> COF2 + NO. The resulting COF2 with a C-13 content near 50% is easy to convert to CO2 or CO for further enrichment by a nonlaser process. We measured the dependence of the fraction of dimerised CF2 on NO2 pressure p(NO2) and the amount of NO2 required to suppress dimerisation on the dissociation yield. Both agree with a kinetic model using known rate constants. For the range of the dissociation parameters ((CF2)-C-13 yield of 10% per pulse, isotope selectivity of 130) of practical interest, 95% of the CF2 produced is oxidized at p(NO2) approximate to 1/2p(CHClF2). In the absence of NO2, major (20%-35%) losses of CF2 at the metal walls of the irradiation system were observed. Addition of NO2 suppresses them. For comparison, we also used O-2 as a scavenger in CHClF2 dissociation. NO2 is by orders of magnitude more efficient.