Emission spectra of three isotopomers of helium hydride (4HeH, 3HeH, and 3HeD) in the visible spectral region have been acquired using proton-beam irradiation of dense helium gas ( 150 Torr) at 4.2 K in the presence of some solid hydrogen or deuterium. Besides the previously reported D 2l:+ -A 2l:+ transition, near 550 nm, a second transition near 640 nm, identified as the D 2l: + _ B 2n, has been acquired and analyzed. The spectroscopic constants for both transitions have been obtained and

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... ared to the theoretical results based on the latest published potential curves. Further insight into the mechanism for forming HeH will be presented, which indicates that the formation process is sensitive to the hydrogen vapor pressure above the solid.