Direct determination of the dissociation probability in highly focused IR multiple photon dissociation

Abstract

Laser-induced fluorescence (LIF) has been used to directly determine the dissociation probability per pulse in highly focused infrared multiple-photon dissociation (IRMPD). The fluence dependence of CDCl₃ IRMPD has been determined by LIF and FTIR spectrometry. The particular LIF irradiation and detection system’s geometry implemented allowed us to monitor the local CCl₂ radicals concentration in the intersection zone of the observation and the dissociation volumes. The fluence dependence of the LIF intensity was modeled with the cumulative log-normal distribution. The dependence of the global values of the fraction of molecules dissociated per pulse on fluence was obtained from FTIR spectrometry. The dissociation probabilities per pulse were derived from the deconvolution of these values using the cumulative log-normal distribution. A very good agreement between the values of the parameters σ and Φ _sat obtained from the deconvolution technique with those resulting from the fluorescence intensity fit was found, showing the validity of the method proposed.