Absolute Total Scattering Cross Sections for 7Li on He, Ne, Kr, and Xe

Abstract

Absolute total scattering cross sections were measured for the systems Li–He, Li–Ne, Li–Kr, and Li–Xe over a range of primary beam velocities of 0.75–4.75×105 cm/sec corresponding to a range of kinetic energies of 0.04–0.33 eV for Li–He to 0.02–0.79 eV for Li–Xe. The standard deviations of the cross sections were less than 1.2% of the observed cross section and the maximum systematic errors were between −0.3% and +1.4%. The data were deconvoluted for the effect of target motion and were statistically smoothed. The smoothed data had a standard deviation of 0.2%–0.4% which was about 4 times smaller than the standard deviation of the raw data points and which provided a criterion for judging the adequacy of fits for various model potentials. Model potentials with up to 5 variable parameters were fit to the smoothed cross sections by a least squares method. For Li–Kr and Li–Xe 4 potential parameters were determined simultaneously. These experiments were most sensitive to the potential value over a range of limiting impact parameters. For Li–Kr and Li–Xe this range was 6.5–9.2 Å and 7.8–9.7 Å, respectively, and in this region the potential was determined to an accuracy of 3%–4%, with the error arising primarily from systematic errors in the measurement of the cross section.