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, H 3 + , H 5 + , H 7 + and H 9 + . Our dissociation enthalpy for the reaction H 3 + ( H 2 ) n → H 3 + ( H 2 ) n − 1 + H 2 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.