Spectroscopic Identification of Excited Atomic and Molecular States in Electron-Bombarded Liquid Helium

Abstract

Optical and infrared emission spectra of electron-bombarded liquid helium reveal the presence of a number of excited singlet and triplet states of the ${\mathrm{He}}_2$ molecule, including the $a{{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}$ metastable state. The observed liquid spectra show vibrational and unresolved rotational structure. There is also preliminary evidence that excited atomic states, including the metastable $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ state, are populated in the liquid.