Vacuum-ultraviolet emission from proton-excited helium gas

Vacuum-ultraviolet (vuv) studies were made of the emission from helium gas excited by 4-MeV protons, under conditions where the gas purity was monitored by concomitant total-ionization measurements. The relative intensity of the 584- resonance line was studied from 0.01 to 100 Torr. Three continua, near 600, 675, and 800, respectively, were investigated from a few Torr to 800 Torr. Our studies of intensity as a function of pressure are consistent with the interpretation that the 675- continuum is the bound-continuum transition Du+1→Xg+1 in the helium diatomic molecule, where the D state is formed by three-body collisions involving the atomic 2P1 state. Some of the 800- continuum, as well as the narrow continuum near 600, is produced, most likely, from a similar process involving emission from the Au+1 molecular state, created from three-body conversion of a 2S1 atomic state. Certain other details are given on the energy pathways following charged-particle excitation of helium gas, and comments are made on some of the recently published emission data for liquid helium.