Vibrational motion effects on molecular polarizabilities. Shifts in vibrational transition frequencies and transition moments of lithium hydride from applied electrical fields

Abstract

Lithium hydride has been used to provide representative information on the effects of vibrational motion on molecular polarizabilities. Dipole and quadrupole polarizability and hyperpolarizability tensors were calculated using derivative Hartree–Fock (DHF) theory. Many of the calculated tensor elements were found to be changing with internuclear separation even in the vicinity of the equilibrium. Vibrational wave functions obtained from a numerical vibrational analysis were used to vibrationally average the electrical properties (tensor elements) of the lowest four vibrational states, and this showed that the averaged polarizabilities of the states have important differences. A manifestation of these differences is that there are shifts in the vibrational transition frequencies along with changes in the transition moments of LiH from applying electrical fields and field gradients. Field gradients can augment the shifts arising from uniform axial fields. This was determined by variationally finding vibrational state energies and transition frequencies as a function of the applied electrical potential.