Temperature dependence of the 31P excitation transfer cross section of helium

Abstract

Inelastic collisions between helium atoms in 31P and 11S states can result in radiationless transfers of excitation. Measurements were made to determine the cross section of the excitation transfer and its variations with the relative velocity of interacting atoms. The collision process was investigated in low density (1015–1018 atoms/cm3) helium gas at four different temperatures between 296°K and 22°K. A 30 KeV electron beam provided primary excitation of the 31P state. The cross sections were found to be 1.6(± 0.3)× 10−15cm2 at 296°K, 1.3(± 0.8)× 10−15cm2 at 214°K, 1.1(± 0.2)× 10−15cm2 at 82°K, and 1.7(± 0.3)× 10−15cm2 at 22°K. A comparison of the experimental results with the predictions of the Stueckelberg theory for imperfect resonance excitation transfer was made. Results indicate possible dipole-quadrupole and quadrupole-quadrupole interactions.