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

Abstract

Theoretical and experimental collision induced spectra associated with the transitions 2P → 3D * , 3P * as well as 3S → 2S in Li * Ne are compared. By means of quantum mechanical simulations, using new ab initio (AI) and semiempirical (MP) potentials and transition moment functions, the contributions from free-free and bound-free transitions on the individual molecular channels to the spectra are analysed and the accuracy of the potentials is tested. In particular, from the excitation spectra 2P → 3D measured with absolute intensity scaling, the experimental 3D potential in the barrier region 8-15 a 0 is obtained by inversion. It is found that the barrier parameters of the AI method reproduce the experimental values within error limits, whereas the barrier height from the MP approach is off by about 100 cm −1 . Beyond the barrier maximum the theoretical energies decrease faster than the experimental ones. The experimental 3S → 2S spectrum is well reproduced by the calculations with the AI data set, showing that the latter are accurate within their limits of confidence.

An Accurate Description of the LiNe X 2Σ+, A 2Π, and B 2Σ+ States

“…Sadlej and Edwards 19 using complete active space perturbation theory (CASPT2), MRCI, and coupled-pair functional (CPF) 21 methods coupled with nearly quadruple-ζ quality basis sets obtained D e = 214 cm -1 , in complete accordance with the experimental value of Lee and Havey, , but, on the other hand, their r e , ω e , and ω e x e values deviate significantly from experiment, Table . Sohlberg and Yarkony 18 and Behmenburg et al pointed out that the neglect of the basis set superposition error (BSSE) correction was the most probable cause of the inconsistent results of Sadlej and Edwards . Our calculations prove that, indeed, there exists a severe BSSE problem in the LiNe (A 2 Π) system, which can only be remedied by using very large basis sets (vide infra).…”

“…Bililign et al, performing BSSE-corrected MRCI-effective core potential (ECP) calculations, obtained satisfactory D e agreement with experiment (Table ) but with an r e value ∼0.16 Å longer, probably due to their ECP approach. Finally, the recent BSSE-corrected coupled electron-pair approximation (CEPA-0) 23 calculations of Behmenburg et al, the largest so far in the literature, give D e = 168 cm -1 while their r e , ω e , and ω e x e values are toward the correct direction.…”

“…e Second-order CI + Davidson correction, [(4s3p2d1f) Li /(5s4p3d2f) Ne ] basis, ref . f Coupled electron-pair approximation, [(8s5p3d3f2g) Li /(11s7p5d4f3g) Ne ] basis, BSSE-corrected, ref .…”

One and Two-Electron Investigation of Electronic Structure for Ba+Xe and BaXe van der Waals Molecules in a Pseudopotential Approach

“…Again, these strong variations can be related to the corresponding avoided crossings in the potentials. Transition dipole moment curve between the ground state X 1 Σ + ( 1 S) and the first state 1 1 Σ + ( 1 D) is important in the study of optical transition in alkali–rare-gas collision in 1 S– 1 D excitation. As can be seen in Figure this curve reaches a maximum of 1.73 a.u.…”

Pressure-broadened atomic Li(2s-2p) line perturbed by ground neon atoms in the spectral wings and core

“…The fluorescence intensities of the alkali resonance lines induced by the buffer-gas in the wings are measured as a function of the wavelength and cell temperature. Various technical methods are used, namely, the laser induced fluorescence, [15][16][17] the two-step laser excitation, [18] the Doppler free two-photon spectroscopy, [19] the combination of the scattering and laser-spectroscopic measures, [20] and the high resolution laser spectroscopy including rotational analysis. [21] In the present particular case, the quantal computations of the LiNe emission spectra made by Mason, [22] based on PECs and TDMs computed by two different methods, namely, the model potential and pseudopotential, are in clear disagreement with the available experimental data measured at T = 670 K by Scheps et al [15] and at T = 130 K, 300 K, and 670 K by Havey et al [23] In this paper, we perform full quantum-mechanical calculations of the far-wing emission and absorption coefficients and line-core width and shift of the Li(2p-2s) resonance spectral line.…”