Optical transitions in excited alkali + rare-gas collision molecules and related interatomic potentials:

Abstract

A comparison is made of experimental far-wing profiles for the system Li(2P → 3D)He with quantum calculations of thermally averaged free-free continua. Using input adiabatic potentials and transition moment functions from both ab initio and semi-empirical approaches, the comparison shows: (i) new ab initio potentials for Li * (2P, 3P, 3D)He reproduce the spectral positions of the observed rainbow satellites well; the height of the 3D barrier predicted agrees with experiment to within ±15 cm −1 , whereas its position is too large by 0.3 a 0 ; (ii) potentials obtained with various semi-empirical methods reproduce the satellite structure qualitatively, but are generally too repulsive in the 3D state at intermediate and large internuclear separations; (iii) transition moment functions for the asymptotically forbidden 2P → 3P transitions reproduce, with different degrees of accuracy, the intensity of the red-wing satellite related to the 3P potential extremum around 12 a 0 . The vibrational energies in the 2P and 3D states calculated with the ab initio potentials reproduce to within a few cm −1 those obtained from rotationally resolved band spectra reported in the literature.

Theoretical study of pressure broadening of lithium resonance lines by helium atoms

“…[18] for 2.0 ≤ R ≤ 2.75 and Ref. [19] for 3.0 ≤ R ≤ 20.0 for the A 2 Π state, and from Ref. [20] for R = 2.0 and Ref.…”

Accurate ab initio determination of the van der Waals interaction in the X 2Σ+ ground state of LiHe

“…Though these systems have a very simple electronic structure with just one valence electron outside spherical cores, accurate potential curves are available neither for the ground nor for excited states. The numerous attempts to determine such potential curves by means of model potential, pseudopotential or other semiempirical effective core potential calculations (see [1] for the case of LiHe) did not lead to interaction potentials with the desired accuracy. Therefore, theoretical treatments of the dynamics of cold collisions or the index of refraction [6][7][8] are still based on potential curves which are constructed more or less empirically from vibrational data for small internuclear separations and van der Waals expansions for the long-range part, e.g.…”

A Fragile Union Between Li and He Atoms

“…The long-range coefficients C 6 are taken from the calculations of Zhu et al [20], and C 1 and C 2 are determined by fitting to the potentials calculated by Behmenburg et al [19]. We first performed single-channel calculations of the energy levels of the A 2 Å and B 2 AE model potentials.…”

“…However, the lambda doubling is sensitive to the exact form of the B 2 AE potential: both to the choice of which theoretical potential we use [19,21] and whether we fit it to a Buckingham or Lennard-Jones model potential. We find the splitting between the negative parity J 0 ¼ 1=2 and the lower J 0 ¼ 3=2 states is 0:180 AE 0:005 cm À1 ; the error is estimated from the different results obtained for different B 2 AE model potentials.…”