Total Cross Sections for the Scattering of Potassium by Helium, Neon, Argon, Krypton, and Xenon

Abstract

Abstract Total cross sections for the scattering of potassium by He, Ne, Ar, Kr, and Xe have been measured in the thermal energy range. The potassium beam and the scattering gases had Maxwellian velocity distributions. The angular resolution of the apparatus was 2.62 min of arc, so that quantum mechanical calculations could be applied. If a van der Waals potential, V=−C⁄r6, is assumed for the long range intermolecular forces, the total cross section may be related to the constant, C, as follows;(Remark: Graphics omitted.), where p is a constant. In the present experiments care was taken to avoid the pumping effect of a McLeod gauge in the measurement of the pressure in the scattering chamber. The Ga0 function denned by Berkling et al. was used to derive an absolute total cross section from a measured effective total cross section. The van der Waals constants calculated from the measured total cross sections were compared with the theoretical values. The present values were about 25 percent smaller than the theoretical values for the Ar, Kr, and Xe systems. The differences for the He and Ne were considerably larger, with the theoretical values larger than the experimental by a factor of two or three.