Sharp spectral lines observed in gamma-ray ionized parahydrogen crystals

We have observed sharp infrared spectral lines ( Deltanu approximately 60 MHz FWHM) in gamma-ray ionized para- H2 crystals. The lines are assigned to the Q1(0) transition of H2 near H+3 and H-, which becomes optically active and Stark shifted by the Coulomb fields of the ions. A simple model calculation gives a spectrum which agrees approximately with the observation. The spectrum stays the same over many days, demonstrating the stability of the ionized system. The remarkable sharpness and reproducibility of the line positions indicate uniformity of the local structure surrounding the charges.