Previous work on the HM+–He complexes (M = Be–Ra) has been extended to the cases of the heavier rare gas atoms, HM+–RG (RG = Ne–Rn). Optimized geometries and harmonic vibrational frequencies have been calculated using MP2 theory and quadruple-ζ quality basis sets. Dissociation energies for the loss of the rare gas atom have been calculated at these optimized geometries using coupled cluster with single and double excitations and perturbative triples, CCSD(T)theory, extrapolating interaction energies to the basis set limit. Comparisons are made between the present data and the previously obtained helium results, as well as to those of the bare HM+ molecules; furthermore, comparisons are made to the related M+–RG and M2+–RG complexes. Partial atomic charge analyses have also been undertaken, and these used to test a simple charge-induced dipole model. Molecular orbital diagrams are presented together with contour plots of the natural orbitals from the quadratic configuration with single and double excitations (QCISD) density. The conclusion is that the majority of these complexes are physically bound, with very little sharing of electron density; however, for M = Be, and to a lesser extent M = Mg, some evidence for chemical effects is seen in HM+–RG complexes involving RG atoms with the higher atomic numbers.
The authors are grateful for the provision of computing time by the EPSRC under the auspices of the NSCCS. We are also grateful for access to the University of Nottingham High Performance Computing Facility. The EPSRC are thanked for funding (Grant No. EP/I012303/1) and for the provision of a studentship to J.P.H. W.H.B. is grateful to the Department of Chemistry at the University of Utah for travel funding, allowing visits to the University of Nottingham.
I. INTRODUCTION II. COMPUTATIONAL METHODOLOGY III. RESULTS AND DISCUSSION A. Geometries B. Harmonic vibrational frequencies C. Atomic charges and dissociation energies D. Contour plots, molecular orbital (MO) diagrams and H(R) IV. CLOSING REMARKS AND CONCLUSIONS