Infrared multiphoton dissociation of CClF2CH2Cl by relatively low-fluence CO2 laser irradiation

Abstract

Infrared multiphoton absorption (IRMPA) and dissociation (IRMPD) of CClF₂CH₂Cl have been studied by low-fluence CO₂ laser irradiation (< 1.0 J cm^–2). Laser beams of spatially uniform intensity, obtained by mild focusing and a short irradiation cell length, were used. The IRMPD yields were measured as a function of reactant pressure, added-gas pressure, laser-energy fluence and laser wavenumber, and the IRMPA was measured as a function of reactant pressure, added-rare-gas pressure, and laser-energy fluence. The results of the IRMPD yields plotted against reactant and added-gas pressure show that molecular collisions play an important role in the excitation process. The effects of the reactant pressure and added-rare-gas concentration upon the product yield can be interpreted by a combination of some positive and negative effects of molecular collisions. On the other hand, the dissociation yields obtained as a function of added CF₂CHCl pressure suggest that the relaxation of anharmonicity bottlenecking by resonant vibrational energy transfer is also important for IRMPD of this molecule. It can be seen that the other experimental results, i.e. the results of the IRMPA experiments and the frequency dependence of the IRMPD yield are consistent with the above interpretation.