Calculation of the vibron band and of the vibron–phonon combination bands in the ir and Raman spectra of solid α-CO

Abstract

The observed gas‐to‐solid shift, splitting, and intensity ratio of the vibrational band in solid α‐CO and the shifts of CO isotopes suspended in solid ¹²C¹⁶O and in N₂ matrices have been studied by calculations based on known gas‐phase and matrix properties. Equations and numerical results for the crystal sums of the various intermolecular interactions are tabulated. It has been shown that the random distribution of the two possible orientations of the CO molecules modifies the dipole–dipole interaction in such a way that the ir spectrum is not affected whereas the Raman spectrum is spread over the entire vibron band. The splitting in the ir spectrum reported by Dubost is interpreted as LO–TO splitting which becomes visible because of nonnormal incidence. The vibron–phonon combination bands have been calculated using electrical anharmonicities, i.e., the bilinear dependence of the polarizability and of the dipole moment on internal and external coordinates. An ellipsoidal cavity has been assumed to compute the influence of the local field on the Raman intensity of the split vibron bands and on the intensity ratio of the vibron and the sideband in solid α‐CO and α‐N₂.