Collisionally Induced Bottleneck Weakening in IR Multiphoton Dissociation

Abstract

An extension of the method of McRae et al. is proposed to quantify the contribution of the distinct collisional processes to the total yield obtained in infrared multiphoton dissociation experiments. The extension consists of the introduction of a substrate pressure dependence in the parameter representing one homogeneous collision. This allows the application of the method at a pressure where the collision time is of the order of the temporal width of the laser pulse and the discrimination between the different processes associated in a given collisional sequence. We have tested the reliability of this extended method by applying it to the multiphoton dissociation of CF2HCl, where the dependence of the dissociation yield on initial pressure and laser fluence has been investigated. We have shown that the homogeneous collisions occurring during the laser pulse may play a fundamental role in the weakening of the bottleneck absorption effects. It has been also suggested that fluence is the main excitation parameter for fixing the pressure interval along which dissociation can be regarded as collisionless.