Observation of theΔJ=4Pure Rotational Transitions in SolidH2and the Inference of the Phonon Density of States

A pure rotational $U$-type transition ($\Delta J=4\mathrm{}$) in solid parahydrogen has been recorded by using a high sensitivity infrared spectrometer. On the assumption of a rigid lattice, the measured intensity led to a value of 0.335 (in atomic units) for the hexadecapole moment of molecular hydrogen. Electric quadrupole-quadrupole interaction effects have been identified in the spectra. It appears possible to extract the phonon density of states in solid ${\mathrm{H}}_2$ from the phonon branch ${U_0}^R\mathrm{}\left(J\right)\mathrm{}$.