Translational and rotational spectra in the fundamental infrared band of liquid and solid parahydrogen

The Q₁(0) and Q₁(0)+S₀(0) infrared bands have been studied in liquid and solid para-H₂ with particular regard to their translational sidebands. In the liquid, their line shapes are well fitted by a model in which the excited particle is encapsulated. In the solid, the phonon sidebands reproduce the main features of the density of states (DOS), as extracted from neutron scattering. The S₁(0)+S₀(0) band shows a pure rotonic line shape which is well described by recent DOS calculations.