Effective Collision Cross Sections of the Alkali Atoms in Various Gases

Abstract

The mean free paths and effective collision cross sections of neutral atoms of Li, Na, K, Rb and Cs were measured in ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, He, Ne and A by the method of molecular beams. The beams were sufficiently narrow and the scattering gas was confined to a region sufficiently small that a resolution of one minute of arc was attained. The results show a larger collision cross section in ${\mathrm{D}}_2$ than in ${\mathrm{H}}_2$ for all the alkalis with the exception of Li. This effect is interpreted as a consequence of the smaller spacing of the ${\mathrm{D}}_2$ rotational levels. The results in general are in qualitative agreement with the quantum theory of collisions.