Interaction potentials of uranium cations with rare gases (RG) and transport of U+ in RG (RG = He, Ne, Ar, Kr, and Xe)

Mobility of the Singly-Charged Lanthanide and Actinide Cations: Trends and Perspectives

The current status of gaseous transport studies of the singly-charged lanthanide and actinide ions is reviewed in light of potential applications to superheavy ions. The measurements and calculations for the mobility of lanthanide ions in He and Ar agree well, and they are remarkably sensitive to the electronic configuration of the ion, namely, whether the outer electronic shells are 6s, 5d6s or 6s². The previous theoretical work is extended here to ions of the actinide family with zero electron orbital momentum: Ac⁺ (7s², ¹S), Am⁺ (5f⁷7s ⁹S°), Cm⁺ (5f⁷7s^{2 8}S°), No⁺ (5f¹⁴7s ²S), and Lr⁺ (5f¹⁴7s^{2 1}S). The calculations reveal large systematic differences in the mobilities of the 7s and 7s² groups of ions and other similarities with their lanthanide analogs. The correlation of ion-neutral interaction potentials and mobility variations with spatial parameters of the electron distributions in the bare ions is explored through the ionic radii concept. While the qualitative trends found for interaction potentials and mobilities render them appealing for superheavy ion research, lack of experimental data and limitations of the scalar relativistic ab initio approaches in use make further efforts necessary to bring the transport measurements into the inventory of techniques operating in "one atom at a time" mode.

Transport coefficients of He(+) ions in helium

This paper demonstrates that the transport coefficients of (4)He(+) in (4)He can be calculated over wide ranges of E/N, the ratio of the electrostatic field strength to the gas number density, with the same level of precision as can be obtained experimentally if sufficiently accurate potential energy curves are available for the X(2)Σu (+) and A(2)Σg (+) states and one takes into account resonant charge transfer. We start by computing new potential energy curves for these states and testing their accuracy by calculating spectroscopic values for the separate states. It is established that the potentials obtained by extrapolation of results from d-aug-cc-pVXZ (X = 6, 7) basis sets using the CASSCF+MRCISD approach are each in exceptionally close agreement with the best potentials available and with experiment. The potentials are then used in a new computer program to determine the semi-classical phase shifts and the transport cross sections, and from these the gaseous ion transport coefficients are determined. In addition, new experimental values are reported for the mobilities of (4)He(+) in (4)He at 298.7 K, as a function of E/N, where careful consideration is given to minimizing various sources of uncertainty. Comparison with previously measured values establishes that only one set of previous data is reliable. Finally, the experimental and theoretical ion transport coefficients are shown to be in very good to excellent agreement, once corrections are applied to account for quantum-mechanical effects.

Mobility of singly-charged lanthanide cations in rare gases: theoretical assessment of the state specificity

High quality, ab initio calculations are reported for the potential energy curves governing the interactions of four singly-charged lanthanide ions (Yb(+), Eu(+), Lu(+), and Gd(+)) with the rare gases (RG = He-Xe). Scalar-relativistic coupled cluster calculations are used for the first three S-state ions, but for Gd(+)((10)D°) it is necessary to take the interaction anisotropy into account with the help of the multi-reference technique. The potential energy curves are used to determine the ion mobility and other transport properties describing the motion of the ions through the dilute RG, both as functions of the temperature, T, in the low-field limit, and at fixed T as functions of the ratio of the electrostatic field strength to the gas number density, E/N. The calculated mobilities are in good agreement with the very limited experimental data that have become available recently. The calculations show a pronounced dependence of the transport properties on the electronic configuration of the ion, as well as a significant effect of the spin-orbit coupling on the transport properties of the Gd(+) ion, and predict that state-specific mobilities could be detectable in Gd(+)-RG experiments.