Theoretical investigation on intermolecular interactions between HCN and HNC: The nature and thermodynamic properties

Geometries, interaction energies, atomic charges and charges transfer for four hydrogen-bonded dimers between HCN and HNC (HCN-HCN, HCN-HNC, HNC-HCN and HNC-HNC) were studied at the MP2/aug-cc-pVTZ level. After MP2 electron correlation, BSSE and ZPE correction, the greatest corrected intermolecular interaction among the dimers is −25.932 kJ mol−1. To reveal the nature of intermolecular interactions in the dimers, a SAPT decomposition analysis on interaction energy was performed. Based on the statistical thermodynamic method, the thermodynamic properties of the title system had been also calculated at different temperature and pressure, the results show that at an analogous environment of comets (the temperature is lower than 100.00 K and the pressure is larger than 0.01 Pa), the formation process of the dimers is spontaneous, indicating that either HCN or HNC could probably exist as dimers rather than as monomers.