The frequency shifts of the vibrational and rotational transitions of H2, D2, and HD mols. trapped in solid Ar are calcd. at zero temp. and at pressures 0 ? P ? 373 kbar. 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 calcd. 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, (1984), but less so with those of Prochaska and Andrews (1977). The calcd. local-mode frequencies of the impurity mols. in the solid at P = 0 are also in good agreement with expt., esp. 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. [on SciFinder (R)]