Infrared spectroscopic studies of the rare gas atom perturbed S1(0) rovibron band of solid parahydrogen

We report high resolution infrared absorption studies of rare gas (Rg) atom doped solid parahydrogen in the hydrogen S₁(0) region around 4486 cm⁻¹. At low Rg atom concentrations (∼0.1%), satellite transitions appear in the S₁(0) region due to rovibrational excitation of parahydrogen molecules with one nearest-neighbor Rg atom. The Ne satellite feature differs qualitatively from the Ar, Kr, and Xe satellite features for reasons described within. The frequency of the S₁(0) satellite features linearly shift to lower energy as the polarizability of the Rg atom increases while the absorption coefficients increase with the square of the Rg atom polarizability. Rotational calculations are performed for H₂ with a nearest-neighbor Rg atom assuming a rigid hexagonal close-packed lattice structure. The calculated fine structure of the S₁(0) satellite features agree qualitatively with lifting of the 2J+1 degeneracy of the v = 1, J = 2 upper state caused by the anisotropy in the Rg-H₂ intermolecular potential. The discrepancy between the calculated and measured Rg atom S₁(0) satellite features may signal partial delocalization of the J = 2 roton onto neighboring parahydrogen molecules.