Knowledge Bank

The observed forbidden pure rotational transitions in solid $H2$ are characterized by a sharp ``zero phonon line'' that is always accompanied by a broad phonon branch. The absorption coefficient for solid hydrogen has been calculated for the pure rotational transitions where the rotational quantum number increases by two or four units. For a particular assumption of the dispersion relationship, the absorption coefficient can be simply related to the single phonon density of states. The density of states obtained from the measured absorption coefficient in solid $H2$ and this calculation is compared with that obtained by neutron scattering measurements.