Effects of addition gases on the IR multiphoton dissociation of haloethanes

Abstract

The effects of addition gases on the rate of the IR multiphoton dissociation (IRMPD) of CClF₂CH₂Cl have been studied. He, CF₄, CF₃CDBrCl and CCl₂CF₂ were employed as the addition gases and IRMPD yield was measured as a function of addition gas mole fraction. The results revealed that molecular collisions play an important role in the excitation process and that the reaction rate is determined by the competition of two collision induced processes, one of which suppresses, and the other enhances, the reaction. In the case of 961.9 cm^–1 irradiation, both effects have been clearly observed, whereas in the case of 1023.2 cm^–1 irradiation, the latter effect seems weak. The results also show that the addition of CF₄ or He always lowers the reaction rate. We conclude that the relaxation of the anharmonicity bottleneck by a resonant vibrational-energy transfer is important for IRMPD of this molecule.