Inelastic Excitation Transfer in Helium

When the positive column of a helium glow discharge is irradiated with intense 5016 Å (21S−31P) light, the population of the 31P state can be markedly increased without affecting the discharge parameters. The resulting enhancement of radiation from the n=3 states allows an upper limit of 4×10−17 cm2 to be placed on the cross section for transfer of excitation by neutral collision in the reaction He(31P)+He→He(33P)+He. This is to be compared on the one hand to reported values ranging from 1.3 to 7.8 times the gas-kinetic cross section, 1.5×10−15 cm2, and on the other to a different interpretation of similar experimental results that does not require the above reaction with its violation of the Wigner spin-conservation rule.