Deexcitation of Helium2S1and2S3Atoms in Fast Collisions with Normal Helium Atoms

Abstract

Cross sections for deexcitation of helium $2{}_{}{}^1{}_{}{}^{}S$ and $2{}_{}{}^3{}_{}{}^{}S$ atoms in collisions of a helium metastable atomic beam with normal helium atoms have been measured in the laboratory energy range 150-2200 eV. The singlet cross sections are from 20 to 75% larger than the triplet cross sections. Both cross sections were found to obey the general relationship $Q^{\frac{1}{2}}=a-b\ln v$ with an oscillatory structure superimposed upon this monotonic velocity dependence. The magnitude of the triplet cross sections compare favorably with calculated values of the cross section for the symmetric excitation-transfer reaction between $2{}_{}{}^3{}_{}{}^{}S$ and $1{}_{}{}^1{}_{}{}^{}S$ atoms.