Multiphoton dissociation and vibrational mediated dissociation of chlorinated methanes, CH4−nCln (n = 2, 3, 4) at 355 nm
In this paper, the experimental results for the photodissociation, PD, and photoionization, PI, of chlorinated methanes, CH2Cl2, CHCl3, and CCl4, studied by cooled molecular jets and Time of Fly Mass Spectrometry detection, ToF-MS, are presented. Photodissociation processes outcome from multiphoton absorption at 109–1010 W cm−2 intensities at 355 nm laser radiation. The results indicated that photodissociation dominates over photoionization processes as some detected ions are originated from the absorption of up to five photons. The main dissociative channels lead to the formation of H+, C+, CH+, CH2+, 35Cl+, 37Cl+, C35Cl+, and C37Cl+. The analysis of the ratio of ion yield from different isotopologues for each molecule, as a function of the energy per pulse, showed that the formation of the more abundant ions: Cl+ and CCl+, is strongly influenced by changes in the vibrational structure of the excited states as a consequence of the two different stable chlorine atoms. As a first approach to get some insight of the experimental results, the ground state vibrational energy levels for chlorinated methanes, were calculated using Density Functional Theory. From the abovementioned calculations was possible to think that the changes in energy of the vibrational levels drive the ion yield of observed ions due to different isotopic composition of chlorinated methanes.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 220, Issue 1, 30 April 2011, Pages 31–38