Spectral Emission of the Helium Afterglow

Abstract

The spectral emission from a dc pulsed helium discharge for pressures from 5 to 30 Torr has been investigated during the early afterglow using a spectrometer with gated photomultiplier and from the early afterglow through the late afterglow using interference filters with gated photomultiplier. The afterglow spectrum was predominately that of molecular light which was attributed to the collisional-radiative recombination of molecular ions. The time-decay of molecular light at late times indicated ambipolar diffusion control by an ion with a Dap of 710±10 cm2/sec, which corresponds to a μ0 of 16.4±0.2 cm2/V·sec, in good agreement with values reported for the helium molecular ion employing other techniques.