Measurements of Total Cross Sections for the Scattering of Potassium Atoms by Rare Gases

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 velocity of potassium beam is selected by a velocity selector of a slotted disk type. To obtain accurate total cross sections, the pumping effect of a McLeod gauge for the pressure measurements, the fringe effect of the scattering chamber, corrections for angular resolution and for thermal motion of the target gases are taken into consideration. A new type of scattering chamber with a variable length is used to eliminate the error of the effective scattering path length. Velocity dependence of total cross sections has been obtained and glory undulations are observed for potassium-xenon systems. For argon, krypton, and xenon the van der Waals constants are calculated from the absolute total cross sections. The values of CK–Ar, CK–Kr, and CK–Xe are 237, 354, and 535×1060 erg·cm6, respectively, and are in good agreement with the theoretical ones of Dalgarno and Davison. For neon the velocity dependence of the total cross section can not be explained by the van der Waals potential, −C⁄rs, where s=6. For helium the correction factors for thermal motion of the scattering gas are large and the value of s for attractive potential can not be determined unambiguously.