Lattice dynamics in solid oxygen

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Abstract
Lattice dynamical calculations for the bulk α, β, and γ phases of solid O2 and for the monolayer α and β phases have been made in the harmonic approximation. In the α and β phases, atom‐atom 6−12 potentials are employed. In the γ phase, effective potentials are used between molecular centers and only the translational lattice vibrations are calculated. It is found that Laufer and Leroi’s potential parameters give two k=O frequencies at 42.7 and 43.6 cm−1 in the bulk α‐O2, and at 40.7 cm−1 for the degenerate k=0 modes in the β phase. The observed Raman lines for α‐O2 at 43 and 79 cm−1, which are both known to exhibit isotope shifts, are thus tentatively assigned to an accidentally degenerate line and a two‐phonon band, respectively, In view of the possible contribution from anharmonic effects, the agreement of the calculation with experiment (48‐51 cm−1) in β‐O2 may be better than it seems. For the bulk γ‐O2, a discrepancy is observed between the calculated elastic constants and those derived from Brillouin scattering experiments. This discrepancy may be due to the neglect of translation‐rotation coupling. In the monolayer O2, Raman active modes at 28.3 and 40.6 cm−1 for the α phase, and 31.9 cm−1 for the β phase are predicted.