Molecular beam infrared spectroscopy and complex-forming reactions of CH3F in argon clusters

Abstract

A molecular beam of medium-large argon clusters containing CH3F has been characterized by means of photoevaporation infrared laser spectroscopy at several stagnation pressures and CH3F concentrations. Bolometric detection and line tunable, isotopically substituted CO2 lasers have been used. Two spectral features have been assigned to the CH3F monomer and the dependence of their shifts and widths on stagnation pressure has been measured. Concentration studies have allowed us to identify the features produced by the CH3F dimer and to recognize tentatively the effect of the higher polymers. CH3F has also been deposited on the clusters surface by means of the previously introduced pick-up technique. In contrast to the results obtained with the SF6/Ar combination, no peaks could be associated with surface adsorbed species. The CH3F/Ar clusters thus characterized have been made to interact with a side flux of HCl and the ensuing complex-forming reaction has been studied. Both the decrease in the CH3F monomer absorption intensity, and the extra absorption due to the newly formed (CH3F-HCl) complexes, have been used to monitor this dynamic process, which has been found to proceed to completion in a time shorter than 100 μs even for the large clusters (approx. 103 argon atoms) produced by our source at the largest viable stagnation pressure.