Molecular librations of solid CO2 under high pressure based on Kihara core potentials

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Abstract
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.