Elastic and nonelastic cross sections for Ar* (3P)+HBr(X 1Σ)

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Abstract
The energy dependence of the differential scattering of metastable Ar* (3P) by ground state HBr(X 1Σ) has been studied at four relative kinetic energies from 60–160 meV over an angular range of 4–120 deg c.m. The position and curvature of rainbow maxima, which are observed at each energy, are used to obtain LJ(12,6) potential parameters. The position of the minimum rm=4.44±0.8 Å is the same as that for K+HBr, and the well depth, ε=25.2±1.1 meV, is about 4% larger than ε (K+HBr). The scattered intensity shows a distinct falloff at large angles compared to that expected for elastically‐scattered Ar*. This depletion, caused by quenching of Ar*, is analyzed in terms of an optical model to determine the threshold and energy dependence of the quenching cross section. The nonelastic cross section increases from a threshold of 25 meV to a nearly constant value of 41 Å2 at 160 meV. The optical analysis predicts a maximum of 42.5 Å2 at 215 meV.