Intermolecular potential and lattice dynamics of orthorhombic acetylene

The crystal structure and lattice dynamics of orthorhombic acetylene have been calculated with an intermolecular potential consisting of atom-atom and multipole-multipole interactions and including a hydrogen bond. A new assignment of the Raman lattice vibrations is discussed and utilized in the refinement of the potential parameters. The non-transferability of the potential to the cubic phase is attributed to the breaking of the hydrogen bond at the phase transition, and to the large anharmonicity expected for the high-temperature phase.