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 high vibrational overtone state, its electronic properties vary significantly since the energy of excitation is a sizable fraction of the energies of the excited electronic states. Thus the vibrational excitation leads to a significant variation of the intermolecular potential and resultant local distortion of the crystal lattice. Such an effect is sensed by the variation of the splitting of M sublevels of the $J=1$ H₂ impurity 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 ΔB and ε2c upon the v=3←0 vibrational excitation. Using the ab initio anisotropic intermolecular pair potential and simplified models on the vibrational dependence of the potential and crystal distortion, observed values are well explained.