Richard J. Plowright

Theoretical study of Ban+–RG (RG=rare gas) complexes and transport of Ban+ through RG (n=1,2; RG=He–Rn)

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.

Electronic spectroscopy of the Au(6p)–Kr complex

We report electronic absorption spectra, recorded using one- and two-color resonance-enhanced multiphoton ionization spectroscopy, of the Au-Kr complex. The transition is localized on the gold atom, and corresponds to a 6p<--6s atomic excitation; we observe transitions to the D (2)Pi(1/2) and D (2)Pi(3/2) spin-orbit states. In addition, we report the results of ab initio calculations, which consider electronic states arising from the 6 (2)S, 5 (2)D, and 6 (2)P atomic energy levels of Au. Further, we also report an accurate value for the dissociation energy of the ground state of Au-Kr, based on basis set extrapolated RCCSD(T) calculations. The experimental results are discussed in the light of the theoretical ones.

Theoretical study of M(+)-RG2 (M+ = Li, Na, Be, Mg; RG = He-Rn).

Ab initio calculations were employed to determine the geometry (MP2 level), and dissociation energies [MP2 and RCCSD(T) levels], of the M(IIa)(+)-RG2 species, where M(IIa) is a group 2 metal, Be or Mg, and RG is a rare gas (He-Rn). We compare the results with similar calculations on M(Ia)(+)-RG2, where M(Ia) is a group 1 metal, Li or Na. It is found that the complexes involving the group 1 metals are linear (or quasilinear), whereas those involving the group 2 metals are bent. We discuss these results in terms of hybridization and the various interactions in these species. Trends in binding energies, D(e), bond lengths, and bond angles are discussed. We compare the energy required for the removal of a single RG atom from M(+)-RG2 (D(e2)) with that of the dissociation energy of M(+)-RG (D(e1)); some complexes have D(e2) > D(e1), some have D(e2) < D(e1), and some have values that are about the same. We also present relaxed angular cuts through a selection of potential energy surfaces. The trends observed in the geometries and binding energies of these complexes are discussed. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are performed, and it is concluded that the AIM method is the most reliable, giving results that are in line with molecular orbital diagrams and contour plots; unphysical amounts of charge transfer are suggested by the Mulliken and natural population approaches.

Electronic spectroscopy of the 6p ← 6s transition in Au-Ne: Trends in the Au-RG series

We report electronic spectra of the Au-Ne complex, obtained in the vicinity of the Au atomic 6p <-- 6s transition. The structured spectrum found near the (2)P(3/2) <-- (2)S(1/2) transition is analyzed. We also explain the nonobservance of a spectrum close to the 6(2)P(1/2) state, using the results of high level ab initio calculations and insight from previous work on other Au-RG complexes (where RG = Ar, Kr, and Xe). Basis set extrapolated RCCSD(T) potential energy curves are also presented for the X(2)Sigma(+) ground state of Au-Ne, and the derived D(e) value is compared to experimental values. We then present an overview of trends through the Au-RG series: included in this are calculations on the X states of Au-He and Au-Rn, as well as for Au(+)-He. We also report further calculations on the states which arise from the interaction of Au(6(2)P(J)) with the rare gas atoms and include a Franck-Condon simulation of the D(2)Pi(3/2) <-- X(2)Sigma(1/2)(+) transition for Au-Ar. Trends in the spectroscopy across this series are summarized, and the Hunds case (a)/(c) character discussed.

Theoretical study of the X Σ2+ states of the neutral CM–RG complexes (CM=coinage metal, Cu, Ag, and Au and RG=rare gas, He–Rn)

We present high level ab initio potential energy curves for the X Σ2+ electronic states of the CM–RG complexes; where CM is a coinage metal, CM=Cu, Ag and Au and RG is a rare gas, RG=He–Rn. These potentials are calculated over a range of internuclear separations, R, and the energy at each point is corrected for basis set superposition error and extrapolated to the basis set limit. Spectroscopic constants are determined from the potentials so obtained and are compared to available experimental data. The impact of core-valence correlation to the overall interactions within the complexes involving the lighter RG atoms is also considered. We find that there is a surprising continuous decrease in Re in these species from CM-He to CM-Rn and show that this is likely due to a combination of sp hybridization and small amounts of charge transfer.

Theoretical study of Mg+-X and [X-Mg-Y]+ complexes important in the chemistry of ionospheric magnesium (X, Y = H2O, CO2, N2, O2, and O).

Optimized geometries and vibrational frequencies are calculated for Ca(+)-X and Y-Ca(+)-X complexes (X, Y = H2O, N2, CO2, O2, and O), required for understanding the chemistry of calcium in the upper atmosphere. Both MP2 and B3LYP optimizations were performed employing 6-311+G(2d,p) basis sets. In some cases a number of different orientations had to be investigated in order to determine the one of lowest energy, and in cases involving O and O2, different spin states also had to be considered. In order to establish accurate energetics, RCCSD(T) single-point energy calculations were also employed, using aug-cc-pVQZ basis sets. Accurate dissociation energies for the Ca(+)-X and X-Ca(+)-Y species are derived and discussed. Comparison with available experimental results is made where possible.