Hydrogen isotope effects on covalent and noncovalent interactions: The case of protonated rare gas clusters

We investigate hydrogen isotope and nuclear quantum effects on geometries and binding energies of small protonated rare gas clusters (Rg(n)X, Rg = He,Ne,Ar, X = H,D,T, and n = 1-3) with the any particle molecular orbital (APMO) MP2 level of theory (APMO/MP2). To gain insight on the impact of nuclear quantum effects on the different interactions present in the Rg(n)X systems, we propose an APMO/MP2 energy decomposition analysis scheme. For RgH(+) ions, isotopic substitution leads to an increase in the stability of the complex, because polarization and charge transfer contributions increase with the mass of the hydrogen. In the case of Rg(2)H(+) complexes, isotopic substitution results in a shortening and weakening of the rare gas-hydrogen ion bond. For Rg(3)X(+) complexes, the isotope effects on the rare gas binding energy are almost negligible. Nevertheless, our results reveal that subtle changes in the charge distribution of the Rg(2)X(+) core induced by an isotopic substitution have an impact on the geometry of the Rg(3)X(+) complex. (c) 2012 Wiley Periodicals, Inc.