Spectroscopic evidence of interstellar solid hydrogen

Infrared bands observed in the ISO-SWS mission are explained as being emitted from inside hydrogen solids, probably in the relaxation process of recombined H2. Double rotational transitions in solid hydrogen are discussed, and an approximate formalism developed by Van Kranendonk is applied to show the crucial role of the delocalized j = 2 states in the explanation of the observed intensities and widths of zero-phonon bands at wavelengths between 6 and 12 μm. Emission rates and column densities of the prominent features have been estimated with reasonable accuracy.