Comparison of reagent translation and vibration on the dynamics of the endothermic reaction Sr+HF

Abstract

The endothermic reaction Sr+HF(v=0)→SrF+H has been studied as a function of collision energy (4–14 kcal/mole) using a crossed beam geometry in which a seeded HF beam intersects a thermal Sr beam. At the same total energy this reaction is compared to the Sr+HF(v=1, J=1) reaction carried out under beam-gas conditions with a pulsed HF laser as the excitation source. In both cases the SrF products are detected by laser induced fluorescence. Using the Ba+HF→BaF+H reaction as an internal reference, the cross section of the Sr+HF(v=1) reaction is found to be 1–10 times greater than for the Sr+HF(v=0) reaction when the same total energy is supplied as reagent translation. Product internal energy distribution and total relative cross sections as a function of collision energy are also measured. Phase space calculations are able to reproduce most of these results. This agreement and other arguments suggest that the Sr+HF reaction often proceeds via multiple encounters which scramble the reagent energy modes during the course of a reactive collision.