Molecular Beam Study of the K+I2 Reaction: Differential Cross Section and Energy Dependence

A molecular beam study of the reactive and nonreactive scattering of a velocity-selected K beam crossed with a thermal I2 beam is described. Velocity analysis yielded the recoil velocity-angle distribution of product KI flux. The energy dependence of this flux distribution was determined from measurements at several incident K beam velocities, corresponding to a range of collision energies Ē from 1.9 to 3.6 kcal/mole. Computational methods were developed to extract the c.m. differential reactive cross section functions (angular and recoil-energy distributions) from the laboratory data. In accord with previous literature on related systems, the reactive cross section is “forward peaked” and most of the exoergicity (some 40 kcal/mole) goes into internal excitation of the KI product. However, there is also significant KI scattering at wide angles and with large recoil energies. The c.m. angular and recoil-velocity distributions are some-what coupled (i.e., nonfactorizable). An increase in Ē from 1.9 to 3.6 kcal/mole produces only a slight change in the shape of the c.m. differential cross section, accompanied by a small decrease (<̃ 20%) in the magnitude of the reaction cross section. Measurements were also made on the angular and velocity distributions of the nonreactively scattered K over the same energy range.