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

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.