Theoretical study of the spectral shift of the absorption line of Rb and Cs in liquid helium

A CASPT2 study of the spectral shift of the resonance emission lines of Rb and Cs embedded in liquid He

“…basis sets (DZP and def2-QZVP) resulting in a cluster radius between 6.2 Å and 6.8 Å [18]. For the Cs-He cluster the minimum is found to be located at 6.93 Å and TDDFT calculations indicate a size of 6.5 -6.7 Å [18], while relativistic density functional calculation shows a minimum at 5.7 Å [41].…”

“…For the Cs-He cluster the minimum is found to be located at 6.93 Å and TDDFT calculations indicate a size of 6.5 -6.7 Å [18], while relativistic density functional calculation shows a minimum at 5.7 Å [41]. Classical Monte-Carlo simulations indicate [18] that the first solvation shell of Rbin liquid He is composed of 53 -57 He atoms, with the maximum at 6.7 -7.0 Å. For Cs, the first shell is formed by as much as 58 He atoms and has a maximum at 7.0 Å [18].…”

“…This symmetric configuration of He atoms acts as a perturbation through the pair potential existing between He and the alkali atom and is an approximation to the effect of bulk liquid surrounding. The efficacy of this model has been well tested in calculating the shift of the absorption lines for various alkali and alkaline earth atoms in liquid He which compares well with experimental data and also with those obtained from the more realistic S-QM/MM [15][16][17][18] [37] and (9s4p3d2f/4s3p2d1f) for He [38]. To account for the spin-orbit coupling relativistic correction was obtained based on the Douglas-Kroll Hamiltonian [39,40].…”

“…For the absorption spectra, the cluster model estimates of the shifts compare well with those obtained using the S-QM/MM [15][16][17][18] methodology. Due to dominating van der Waals interaction between He and the central atom only nearest neighbors are mostly effective in producing the shift.…”

“…Subsequently, relativistic model cluster calculations and methods based on sequential use of Monte Carlo simulation followed by quantum mechanics calculations (S-QM/MM) [15][16][17][18] have been very successful in interpreting the change in line positions and profiles connected with the absorption spectra of alkali and alkaline-earth atoms in liquid He.…”