Nuclear quantum effect on the dissociation energies of cationic hydrogen clusters

Ab initio path integral molecular dynamics based on MP2/cc-pVTZ method has been carried out for a series of small hydrogen cluster cations, H3+,H5+,H7+ and H9+. Our dissociation enthalpy for the reaction H3+(H2)n→H3+(H2)n−1+H2 is found to be 5.4, 2.1, and 3.2 kcal/mol, respectively, which are slightly smaller than the corresponding experimental values. It is found that energies of quantum zero-point vibration and anharmonic vibration of the respective cations are important factors to estimate the value of dissociation energy.