Enhanced isotope separation in CF2Cl2 by infrared multiphoton dissociation at elevated temperatures

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Abstract
Isotopic specificity in the infrared multiphoton dissociation of CF2Cl2 has been found to be significantly enhanced by irradiation at elevated temperatures. We have observed the extent of this effect to depend sensitively on laser wavelength. Frequencies to the blue of the ν8 fundamental at 927 cm−1 produce a systematic pattern of varying enhancements, while increased temperatures for irradiation to the red of ν1 at 1120 cm−1 destroy isotopic specificity evident at room temperature. We explain these results by introducing a pumping-frequency specific temperature dependence for the rate of multiphoton excitation, such that, in the bulk gas phase, isotopically selective, temperature dependent pumping competes with collisional scrambling to yield a temperature dependent selectivity. We show that a simple kinetic model, incorporating the quantitative expression of this temperature dependence developed in earlier work, adequately accounts for our observations.