Stability of solid hydrogen coated graphite particles

Abstract

Recently, Wickramasinghe and K. S. K. S. have shown that the extinction curves for graphite particles coated with solid hydrogen reproduce well the observed reddening curve over the observed spectral region. The albedo and phase function for the particles were also shown to be consistent with observations. It was suggested in a qualitative manner that the solid hydrogen mantles could be stable in an interstellar radiation field due to the presence of optically active transitions at frequencies ~10 cm^-1. It is quite possible to get such transitions due to the presence of ortho molecules of hydrogen in the mantle. In this paper we make some detailed calculations on the temperature of grains coated with solid hydrogen and their evaporation rates in interstellar space. It turns out that the temperature of the grains is considerably higher than the temperature required to maintain them.