Anharmonic lattice vibrations in solid N2

Publisher Website
Google Scholar
Abstract
Perturbation theory in terms of the Green's function method is applied to the anharmonic lattice vibrations in solid α-N2. A Lennard-Jones type 6–12 atom-atom potential is used for the intermolecular potential. Cubic and quartic anharmonic terms are retained in the crystal hamiltonian and the phonon correlation functions of one-phonon processes perturbed by these terms are calculated. Band profiles of the optical modes at q = 0 are obtained at temperatures 1, 10, 20 K under a constant volume. It is found that the frequencies of the modes shift to the high-frequency side by 3·9–14 cm-1 from those of the harmonic calculation, because the potential employed here has considerably strong repulsion, and weaker anisotropy than that possessed by the EQQ potential. The large width of the Tg + band and the abnormally wide one of Tu + band are reproduced theoretically. The change of frequency and band width of the Eg mode by temperature at a constant volume are compared with the experiment by Medina and Daniels.