Frequency shifts of vibrational and rotational states of dilute H2, D2, and HD impurities in solid Ar under pressure

The frequency shifts of the vibrational and rotational transitions of H2, D2, and HD molecules trapped in solid Ar are calculated at zero temperature and at pressures 0< or =P< or =373 kbar. It is found that the pure vibrational and rotational-vibrational transition frequencies are strongly red-shifted in the solid at P = 0, compared to gas-phase values, and the agreement with Raman scattering measurements is generally good. The calculated pure rotational transitions also show a small red shift at P = 0 in the solid and are in generally good agreement with the measurements of Jodl and Bier, but less so with those of Prochaska and Andrews, who, except for D2(Ar), measure small blue shifts. The calculated local-mode frequencies of the impurity molecules in the solid at P = 0 are also in good agreement with experiment, especially when thermal corrections are considered. With increasing pressure all transition frequencies and the local-mode frequencies are strongly blue-shifted with respect to P = 0 solid values