VARIATION OF INTERMOLECULAR INTERACTION AND LOCAL LATTICE DISTORTION OF PARAHYDROGEN CRYSTALS UPON VIBRATIONAL-EXCITATION

When a hydrogen molecule in a parahydrogen crystal is excited to a hig h vibrational overtone state, its electronic properties vary significa ntly since the energy of excitation is a sizable fraction of the energ ies of the excited electronic states. Thus the vibrational excitation leads to a significant variation of the intermolecular potential and r esultant local distortion of the crystal lattice. Such an effect is se nsed by the variation of the splitting of M sublevels of the J=1 H-2 i mpurity that causes the overtone transition. In this paper we attempt to theoretically explain the observed large variations of the pair and crystal-field splitting parameters Delta B and epsilon(2c) upon the u psilon=3<--0 vibrational excitation. Using the nb initio anisotropic i ntermolecular pair potential and simplified models on the vibrational dependence of the potential and crystal distortion, observed values ar e well explained. [S0163-1829(98)04901-7].