Rotational energy effect upon the branching fraction for reactive decay of the RbF+K collision complex

Abstract

The influence of the rotational energy of the RbF molecule upon its reactivity with K has been measured by the crossed molecular beam technique over a range of relative translational energy ?tr from 3.0–4.5 kcal mol−1. The experiments involve the exoergic reaction RbF+K?[RbFK]→Rb+KF+1.5 kcal mol−1, for which the reactive branching fraction FR(?tr) had been previously measured using velocity-selected but otherwise ’’thermal’’ beams. Following procedures similar to those of Stolte et al. (1977), rotationally cold (’’low-J’’) beams of RbF have been prepared (by a quadrupole state selector) and crossed with a K beam. The reactive yield (Rb flux) and thus the reactive branching fraction FR is found to be significantly greater for the ’’low-J’’ beam than for the ’’thermal’’ beam of RbF. The magnitude of this rotational energy effect, associated with a reduction of some 2.0 kcal mol−1 in the rotational energy of the reagent molecules, is similar to the effect of a comparable reduction in ?tr. Thus, within the uncertainty of the present results, rotational energy of the RbF is equivalent in importance with relative translational energy in influencing the decay of the RbFK collision complex.