VIBRATIONAL DEPHASING OF A POLAR SOLUTE IN A FUSED SALT

We calculate the classical-mechanical vibrational line shape of a pola r, harmonic diatomic molecule dissolved in a fused salt. This model sy stem is chosen to allow exploration of the effects of Coulomb interact ions on vibrational dynamics. The Coulomb interaction is scaled by an effective dielectric constant, whose magnitude is varied to alter rela tive contributions of long- and short-ranged forces to the line shape. Calculations are performed with an analytical theory based on the ins tantaneous normal mode approximation, in which the dynamics of a liqui d are mapped onto the motions of a disordered harmonic network. Result s are compared to calculations based on molecular dynamics simulations of a fused salt. The vibrational line shape predicted by this approac h may be expressed in the form associated with the generalized Langevi n equation, allowing the identification of a frequency-dependent bond friction. The contribution to this generalized friction coefficient fr om long-ranged electrostatic interactions is analyzed.