Interstellar Hydrogen Atoms on Graphite Grains


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.

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  1. 1

    Duley, W. W., Nature, 222, 361 (1969).

  2. 2

    Wickramasinghe, N. C., Interstellar Grains, (Chapman and Hall, London, 1967).

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MCINTYRE, H., WILLIAMS, D. Interstellar Hydrogen Atoms on Graphite Grains. Nature 223, 487–488 (1969).

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