Vibrational spectroscopy of matrix isolated diatomics: The infrared line shape

Abstract

The vibrational line shape of a diatomic molecule imbedded in a solid matrix is computed with the aid of a one dimensional model. It is assumed that the broadening mechanism is the coupling between the vibrations of the system. As a zero order approximation, we use the harmonic vibrations of the lattice with the diatomic impurity. The harmonic modes are coupled by cubic and quartic force constants. All the necessary force constants are computed from semiquantitative interatomic potentials. The width obtained in this calculation is generally too small and nearly temperature independent. The lattice induced shift (total shift minus the shift caused by the anharmonicity of the diatomic) is toward the blue instead of the red, and is temperature dependent.