Deexcitation cross sections of He (2 3S, 2 1S, and 2 1P) by molecules containing group-IV elements

Abstract

Deexcitation cross sections of He(2 ³S), He(2 ¹S), and He(2 ¹P) by C₂H₆, Si₂H₆, CF₄, SiF₄, and SiCl₄ have been measured at a mean collisional energy corresponding to room temperature (295 K) and compared systematically with those by CH₄, SiH₄, and GeH₄ (previously reported) to understand general features of the cross section values dependent on both the electronic states of excited helium atoms and the target molecules containing group‐IV elements and to substantiate further the deexcitation mechanism. In the de‐excitation of the metastable atoms, He(2 ³S) and He(2 ¹S), the magnitude of the cross sections has mainly been ascribed to a short‐range electron exchange interaction. The obtained cross section values for He(2 ³S) are compared with a semiempirical formula and it is concluded that the number of the equivalent electrons which can be ionized with the excitation energy of He(2 ³S) and the lowest ionization potential of the target molecule are of great importance in determination of the cross section values. Systematic comparisons of the deexcitation cross section values of the resonant atom, He(2 ¹P), with theoretical ones have shown an importance of not only deexcitation transition mainly ascribed to a long‐range dipole–dipole interaction between He(2 ¹P) and a target molecule but also a bent trajectory caused by an attractive interaction potential between them to determine the cross section values.