Atomic Emission of the Helium Afterglow

Abstract

The spectral emission from a dc pulsed helium discharge for pressures from 5 to 20 Torr has been investigated during the early afterglow using interference filters with gated photomultiplier. The radiation transmitted by the filters consists generally of both atomic lines and molecular bands and after the termination of the active discharge shows characteristically an initial rapid decrease in intensity followed by a much slower rate. The rapid decrease is due to the atomic radiation, the slower to molecular. By subtracting the molecular emission from the total emission transmitted through an interference filter, the atomic emission is obtained. From the decay curves of the atomic emission, which is the result of collisional‐radiative recombination of He⁺, and the known diffusion loss of He⁺, the rate of conversion of He⁺ into He₂⁺ is found to be 109±6 sec^—1·Torr^—2.