Theoretical modeling of ion mobility in superfluid 4He

A method for calculating hydrodynamic added mass within the framework of time-dependent bosonic density functional theory (DFT) for superfluid He-4 is developed. As a calibration of the model, it is shown to reproduce the classical hydrodynamic limit for purely repulsive interactions. To model real systems for which experimental data are available, the following ions were considered: Be+, K+, Ca+, Sr+, and Ba+ cations as well as the F-, Cl-, I-, and Br- anions. The DFT model requires the ion- helium pair potential data as input, which were obtained from electron structure calculations by employing coupled clusters theory. The resultant static liquid density profiles as calculated by DFT were found to be in good agreement with previously published quantum Monte Carlo data. The calculated added masses for the positive ions correlated directly with the experimentally observed ion mobility data, by which the ions could be separated into two different categories based on the degree of the first solvent shell following the ion. The calculated added masses for the negative ions were found to be in disagreement with the existing experimental data, suggesting the possibility that other negatively charged species were observed in previous experiments. The negatively charged ions are predicted to have mobilities (mu) within the range 0.8-1.0 cm(2) V-1 s(-1) in superfluid helium at 1.3 K with the order mu(I-) > mu(Br-) > mu(Cl-) > mu(F-).