Atomic-Beam Scattering Studies on the Li–Hg System: Quantum Effects and Velocity Dependence of the Cross Sections

Abstract

Measurements of the velocity dependence of the angular intensity distribution of 6Li and 7Li beams scattered by a crossed Hg beam are reported. The Li beams were velocity selected, the Hg beam Maxwellian. Angular intensity distributions were measured at various relative velocities (vr) from 700–1200 m/sec, relative total cross sections (q) from vr=300 to 1350 m/sec. The differential cross sections show expected quantum interferences. Scattering patterns for 6Li— and 7Li–Hg are found to be identical at the same de Broglie wavelength. The over-all angular dependence of the scattering at low angles follows the θ−7/3 relationship characteristic of an r−6 long-range potential. Extrema in the total cross sections q(vr) were also observed. The experimental data were analyzed in terms of a Lennard-Jones (12, 6) potential, but it was not possible to determine a unique set of potential parameters. Comparison of observed and calculated results has yielded three nearly equivalent sets of σ, ε lying within the ranges 2.5≤σ≤3.5 Å, 480°≤ε/k≤1000°K.