We present a comprehensive overview of our current knowledge of the interactions of valence M(nsnp 3P) and M(nsnp 1P1) excited states with H−H, Si−H, and C−H bonds, where M = Mg, Zn, Cd, and Hg. It is proposed that the high reactivity of M(nsnp 3P1) states with H−H and Si−H bonds compared to C−H bonds is due to the lack of steric hindrance in the localized, side-on, M(npπ)−XH(σ*) donor−acceptor molecular orbital interactions, since the Si−H bond length in SiH4 is ∼1.5 Å compared to C−H bond lengths of ∼1.1 Å. It is also concluded that Mg(3s3p 1P1) and Zn(4s4p 1P1) efficiently activate C−H bonds as well as H−H and Si−H bonds not just because of their higher energy but because of better M(npπ)−XH(σ*) energy matches and overlap, which overcomes M(ns)−XH(σ) repulsion and the steric hindrance. It is further proposed that the striking differences in the microscopic mechanisms of attack of C−H bonds by Mg(1P1) versus Zn(1P1) may be due to the fact that the Zn(4s) “core” is substantially (∼0.2 Å) smaller than the Mg(3s) “core”, allowing true insertion of the Zn(1P1) state (but not the Mg(1P1) state) into C−H bonds to form (by surface hopping) long-lived ground-state zinc alkyl hydrides which decompose in a non-RRKM fashion to yield the observed ZnH product. Finally, the experimental results to date (as well as ab initio calculations) indicate that direct, end-on “abstractive” attack of M(nsnp 1P1) states [as well as O(1D2)] of H−H, Si−H, and C−H bonds probably does not occur.

High-level ab initio calculations are performed on the coinage metal cations ͑Cu + , Ag + , and Au + ͒ interacting with each of the rare gases ͓Rg ͑Rg=He to Rn͔͒. The RCCSD͑T͒ procedure is employed, with basis sets being of approximately quintuple-quality, but with the heavier species using relativistic effective core potentials. The interaction potentials are compared to experimental and theoretical data where they exist. In addition, transport coefficients for the mobility and diffusion of the cations in the rare gases are calculated. The latter have involved a rewriting of some of the programs used, and the required modifications are discussed. The mobility results indicate that, rather than being a rare occurrence, mobility minima may be common phenomena. Finally, a new estimate is put forward for the validity of zero-field mobilities in ion mobility spectrometry.

We present high level ab initio potential energy curves for the M(n+)-RG complexes, where n = 1, 2, RG = rare gas, and M = Be and Mg. Spectroscopic constants have been derived from these potentials, and they generally show very good agreement with the available experimental data. The potentials have also been employed in calculating transport coefficients for M(+) moving through a bath of RG atoms, and the isotopic scaling relationship is examined for Mg(+) in Ne. Trends in binding energies, D(e), and bond lengths, R(e), are discussed and compared to similar ab initio results involving the corresponding complexes of the heavier alkaline earth metal ions. We identify some very unusual behavior, particularly for Be(+)-Ne, and offer possible explanations.

We present high-level ab initio potential energy curves for barium cations and dications interacting with RG atoms (RG = rare gas). These potentials are employed to derive spectroscopic parameters for the Ba(+)-RG and Ba(2+)-RG complexes, and also to derive the transport coefficients for Ba(+) and Ba(2+) moving through a bath of the rare gas. The results are compared to the limited experimental data, which generally show reasonable agreement. We identify a large change in binding energy going from Ba(+)-He and Ba(+)-Ne to Ba(+)-Ar, which is not present in Ba(2+)-RG, and show that this is due to significant dispersion interactions in Ba(+)-RG.

Evidence is presented that there is a clear covalent component in the bonding of Au+ to Kr and Au+ to Xe, with some evidence that there may be such bonding between Au+ and Ar; for Au+ and Ne, there is no such evidence, and the bonding seems to be entirely physical. A model potential analysis shows that when all attractive inductive and dispersive terms out to R-8 are properly included in the Au+-Ne case, with an Ae(-bR) Born-Mayer repulsive term, essentially all the bonding in Au+-Ne can be rationalized by physical attraction alone. This is consistent with a natural bond order (NBO) analysis of the Au+-Ne ab initio wavefunctions, which shows the charge on Au+ to be very close to 1.0. In contrast, similar model potential and NBO analyses show quite clearly that physical interactions alone cannot account for the large bond energy values for the Au+-Kr and Au+-Xe complexes and are consistent with covalent contributions to the Au+-Kr and Au+-Xe interactions. Au+-Ar is seen to lie on the borderline between these two limits. In performing the model potential analyses, high-level ab initio calculations are employed [CCSD(T) energies, extrapolated to the complete basis set limit], to obtain reliable values of Re, De and omegae as input. A comparison of the gold-Xe bond distances in several solid-state Au(I, II and III) oxidation-state complex ions, containing "ligand" Xe atoms, prepared by Seppelt and co-workers, with that of the "free" Au+-Xe gas-phase ion is made, and a discussion of the trends is presented.