MOLECULAR LIBRATIONS OF SOLID CO2 UNDER HIGH-PRESSURE BASED ON KIHARA CORE POTENTIALS

Molecular librations at k=0 of solid α-CO2 under high pressure at T=0°K have been studied in terms of Kihara models consisting of both 6-n type potential (n=12 or 9) and the electrostatic quadrupole-quadrupole interaction. A rod-shaped molecular core was utilized to describe the molecular shape. The potential parameters were determined from the observed lattice constant and heat of sublimation at P=0 bar. The calculated libration frequencies at P=0 bar for either n=12 or n=9 models were in good agreement with observed Raman and neutron data. The crystal energies and the libration frequencies at high pressures were computed to obtain, respectively, the P-V relation and the Grüneisen parameters associated with the k=0 modes. Good agreement of the calculated Grüneisen parameters with observed data was attained for the n=9 models. The calculated P-V relation should be compared with experimental data which is not currently available. © 1980 American Institute of Physics.