Quantum Lattice Dynamics of Molecular Solids. II. Application to the Librations of Solid CO2, α-N2, and o-H2

Abstract

The quantum mechanical lattice dynamics formalism developed in the preceding paper for molecular solids is applied to the librational modes at k=0 in solid α‐N₂, CO₂, and o‐H₂, interacting through a quadrupole‐quadrupole potential. Librational wavefunctions are constructed for α‐N₂ and CO₂, and free rotor wavefunctions were used for librons in solid o‐H₂. It is found that the quantum‐mechanical lattice frequencies provide nonnegligible, though not dramatic, corrections to the frequencies calculated in the classical harmonic approximation. For α‐N₂ the quadrupole potential provides a satisfactory description of the anisotropic potential, with the quantum‐mechanical frequencies significantly closer to experiment than the classical ones. For CO₂ the quadrupole potential provides only part of the anisotropic potential.