Abstract
The equilibrium geometries, harmonic vibrational frenquencies, and the dissociation energies of the N2H+−X (X = He, Ne, Ar, Kr, Xe, and H2) complexes were calculated at the DFT, MP2, MP4, CCD, CCSD, and CCSD(T) levels of theory. In all of the rare gas complexes, the DFT, MP2, and MP4 methods tend to produce longer X−H+ (X = He, Ne, Ar, Kr, Xe, and H2) distances than the CCSD(T)-level-predicted value, while the CCD- and CCSD-level X−H+ bond lengths are slightly shorter. For the free N2H+ ion, all level calculations yield reliable results and are congruous with experiments. The predictions of geometrical parameters, dissociation energies, and the red shift of the H+−N stretching mode (ΔωH+-N) in N2H+−He and N2H+−Ne complexes are highly dependent upon the level of electron correlation and the size of the basis set. The DFT method is not reliable for studies of fairly weak interactions between He, Ne and N2H+, however, may be used to obtained the qualitatively correct results for N2H+−Ar and N2H+−H2. For complexes involving heavier atoms, N2H+−X (X = Kr and Xe), the relativistic effects have a minor effect on the geometrical parameters and the H+−N stretching mode. However, the dissociation energy is highly dependent upon the relativistic effects. Moreover, the dissociation energies and the geometrical parameters are sensitive to the size of the basis set.