Interstellar Hydrogen Atoms on Graphite Grains

Abstract

DULEY¹ has recently suggested that the cause of the deficiency of the stellar ultraviolet flux below the Lyman-α line may be due to hydrogen atoms near interstellar grains absorbing at wavelengths shifted from 1216 Å. Duley has calculated the shift in the 1s and 2p levels of an H atom near a pure dielectric grain by placing the atom at the centre of a spherical cavity of radius R₀ in a medium specified only by a dielectric constant K. For K = 1.1→1.4 and R₀ = 2→5a₀, the resultant shift in the Lyman-α line is positive, and on the order of a few tenths of an electron volt, so that absorption would occur at wavelengths shorter than 1216 Å.