International Workshop on Atomic Interactions in Laser Fields - Abstracts
T. Grycuk1, W. Behmenburg2, and V. Staemmler3
1Institute of Experimental Physics,
University of Warsaw, Poland
2Institut für Experimentalphysik, H.H. Universität
Düsseldorf, Düsseldorf, Germany
3Lehrstuhl für Theoretische Chemie, Ruhr-Universität
Bochum, Bochum, Germany
Optical transitions between several electronic states of the Li*He diatomics under the conditions of thermal averaging are simulated by quantum calculations in order to test the interaction potentials and the dipole moment functions involved.
Two types of transitions are considered
(A) the absorption transitions 3(D,P)Λ' → 2PΛ'', generating the spectrum
in the neighbourhood of the Li(3D-2P) line at 610 nm,
(E) the emission transitions 3(D,P,S)Λ' → 2SΣ, resulting in the excimer
bands in the region 320 - 430 nm.
Both kinds of spectra have been investigated in recent years by Behmenburg and coworkers [1], [2] in cell experiments using 2-step laser excitation techniques for gaseous mixture of Li + He at about 700 K. Moreover, the case (A) (detected as an excitation spectrum and expressed in terms of a normalized cross section for the Li (3D) excitation) has been analysed theoretically [3] as well. It has been done by means of quantum simulations of the thermally averaged excitation cross section, limited to free-free transitions, using potentials and dipole transition moment functions obtained with various theoretical approaches. Those calculations indicated, however, the noticable discrepances between simulated and experimental spectrum even for the new ab initio interaction data (AI) reported by Staemmler [3].
In the present work further studies of this problem are undertaken including molecular transitions involving also bound states of the considered system. Calculations are performed within the adiabatic limit for AI data of [3] and [4] as input.
The numerical routine is roughly the same as that described in ref. [5] however, rotational effects are now considered more carefully assuming that the angular momentum coupling for the LiHe molecular states is described by Hund's case b.
Results obtained show that in the case of the absorption transitions (A) taking into account the bound states considerably improves the agreement with experimental spectrum.
In the case of the excimer emission (E), analysed theoretically for the first time in this work, all spectral features observed are well reproduced by the AI data testyfying to accuracy of those data for the bound states correlated with the Li 3(S,P,D)+He asymptotes.