A p r i o r i calculation of the vibron band and of the vibron–phonon and two-phonon combination bands in the Raman spectrum of solid α-N2

Abstract

The observed shift, splitting, and intensity ratio of the vibrational Raman band in solid α-nitrogen as reported by Anderson et al. have been reproduced in a calculation which is based on the quadrupole moments and polarizabilities of N2 in the gas phase. Furthermore, the intensities and shapes of the weak phonon sideband in the N2 stretching region, as well as of the two-phonon sideband in the lattice region, have been calculated by treating these as combination bands which derive their intensities from electrical anharmonicities, i.e., from quadratic dependences of the polarizability on internal and external nuclear displacements. The contributions from mechanical anharmonicities, i.e., from vibron–phonon coupling through third and higher order terms in the vibrational potential, are found to be negligible in these band intensities. The computations of the lattice dynamics are based on a Lennard-Jones plus quadrupole–quadrupole potential.