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The Journal of Chemical Physics

Orientation effects in the scattering of Na(3 2P3/2) and K(4 2P3/2) with rare gas targets at thermal energies

Rudolf Düren, Eckart Hasselbrink

Published Aug 15, 1986• 23 citations
Publisher

Abstract

The σ−/σ+ asymmetry in the scattering of excited Na(3 2P3/2) and K(4 2P3/2) atoms with oriented electronic angular momentum from rare gas targets has been systematically studied. The orientation is achieved by exciting the atoms with circularly polarized laser light, which is directed perpendicularly into the scattering plane. The origin of the asymmetry is discussed on the basis of the close coupling formalism. This reveals the centrifugal part of the interaction to be the only central reason. The asymmetry is observed for all of the different target gases studied (Ne, Ar, Kr, Xe). Quantitatively the observed features change strongly for the different combinations. Model calculations are presented which show the different fine-structure splitting of the alkali atom and the polarizability of the rare gas atoms to be responsible for the variation.

DOI
10.1063/1.451818

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The sigma/sup -//sigma/sup +/ asymmetry in the scattering of excited Na(3 /sup 2/P-italic/sub 3//sub ///sub 2/) and K(4 /sup 2/P-italic/sub 3//sub ///sub 2/) atoms with oriented electronic angular momentum from rare gas targets has been systematically studied. The orientation is achieved by exciting the atoms with circularly polarized laser light, which is directed perpendicularly into the scattering plane. The origin of the asymmetry is discussed on the basis of the close coupling formalism. This reveals the centrifugal part of the interaction to be the only central reason. The asymmetry is observed for all of the different target gases studied (Ne, Ar, Kr, Xe). Quantitatively the observed features change strongly for the different combinations. Model calculations are presented which show the different fine-structure splitting of the alkali atom and the polarizability of the rare gas atoms to be responsible for the variation.

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Coherence transfer accompanying 32P1/2 → 32P3/2 excitation transfer in sodium, induced in collisions with noble gas atoms, has been investigated using methods of sensitized fluorescence. Oriented 32P1/2 sodium atoms were produced by irradiating a mixture of sodium vapor and a noble gas with D1σ+ resonance radiation, and their subsequent collisions with the buffer gas atoms resulted in the simultaneous transfer of coherence and excitation from the 2P1/2 state to the 2P3/2 state. Measurements of the ratio of circular polarizations of the D2 sensitized fluorescence and D1 resonance fluorescence resulted in the following cross sections for coherence transfer. Na–He : 7.1 ± 0.7 Å2; Na–Ne : 6.2 ± 0.6 Å2; Na–Ar : 12.0 ± 1.2 Å2; Na–Kr : 6.8 ± 0.7 Å2; Na–Xe : 6.9 ± 0.7 Å2.

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Disorientation of Na(32P1/2) Atoms, Induced in Collisions with Noble Gases

B. Niewitecka, Tadeusz Skalinski, L. Krause

The cross sections for disorientation of 32P1/2 sodium atoms, induced in collisions with noble gas atoms, have been determined by following the depolarization of Na–D1 resonance fluorescence in relation to noble gas pressure. Sodium vapor at low density, mixed with a noble gas in a fluorescence cell, was irradiated with circularly polarized D1 resonance radiation and the resulting D1 resonance fluorescence, observed in an approximately backward direction, was analyzed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a 'J randomization' model for the collisions, and yielded the following disorientation cross sections which are appropriately corrected for effects due to nuclear spin. Na–He: 28.1 ± 4.0 Å2; Na–Ne: 27.8 ± 4.0 Å2; Na–Ar: 57.0 ± 8.0 Å2; Na–Kr: 78.0 ± 10 Å2; Na–Xe: 87.0 ± 13 Å2.

Canadian Journal of Physics•Oct 15, 1974•7 citations
The σ−/σ+ asymmetry in the scattering of excited Na(3 2P3/2) and K(4 2P3/2) atoms with oriented electronic angular momentum from rare gas targets has been systematically studied. The orientation is achieved by exciting the atoms with circularly polarized laser light, which is directed perpendicularly into the scattering plane. The origin of the asymmetry is discussed on the basis of the close coupling formalism. This reveals the centrifugal part of the interaction to be the only central reason. The asymmetry is observed for all of the different target gases studied (Ne, Ar, Kr, Xe). Quantitatively the observed features change strongly for the different combinations. Model calculations are presented which show the different fine-structure splitting of the alkali atom and the polarizability of the rare gas atoms to be responsible for the variation.
The sigma/sup -//sigma/sup +/ asymmetry in the scattering of excited Na(3 /sup 2/P-italic/sub 3//sub ///sub 2/) and K(4 /sup 2/P-italic/sub 3//sub ///sub 2/) atoms with oriented electronic angular momentum from rare gas targets has been systematically studied. The orientation is achieved by exciting the atoms with circularly polarized laser light, which is directed perpendicularly into the scattering plane. The origin of the asymmetry is discussed on the basis of the close coupling formalism. This reveals the centrifugal part of the interaction to be the only central reason. The asymmetry is observed for all of the different target gases studied (Ne, Ar, Kr, Xe). Quantitatively the observed features change strongly for the different combinations. Model calculations are presented which show the different fine-structure splitting of the alkali atom and the polarizability of the rare gas atoms to be responsible for the variation.
Semiclassical calculations of the quasi-elastic l-mixing and inelastic n,l-changing processes in thermal collisions of a Rydberg sodium atom with rare-gas atoms (Ne, Ar, Kr and Xe) as well as and atoms with Ne are presented in a wide range of principal quantum numbers. The main emphasis is put on the study of the effects in the Rydberg-atom - rare-gas-atom collisions associated with both the short- and long-range (polarization) parts of the electron - perturber interaction. It is shown that the polarization interaction between the highly excited electron and the Ne atom provides the major contribution to the cross section of the l-mixing and n, l -changing transitions. We show that the Ramsauer - Townsend effect in slow electron scattering by the heavy rare-gas atoms significantly affects the values of the cross sections, particularly for the inelastic transitions with large energy transfer. A quantitative explanation of these phenomena is given using the recently developed semiclassical normalized perturbation theory for the Rydberg-atom - neutral collisions combined with the modified effective range theory for scattering of slow electrons by the rare-gas atoms.
The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na--rare-gas (RG) optical collision Na(2{(}^{2}(2S1/2{S}_{1/2}S1/2​)+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na(2{(}^{2}(2Pj{\mathrm{P}}_{\mathrm{j}}Pj​)+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3p2{p}^{2}p2P3/2{P}_{3/2}P3/2​ and 3p 2P1/2^{2}P_{1/2}2P1/2​ states are examined. The cross sections \ensuremath{\sigma}(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis of \ensuremath{\sigma}(j) shows a significant difference between contributions from states of e and f molecular parity. The theoretically calculated detuning dependence of the branching ratio into each fine-structure state is in good agreement with available experimental data for Na-Ar, Na-Ne, and Na-He, as well as the total absorption coefficient for the production of Na 3p atoms. The fine-structure branching ratio for thermal energy collisions shows considerable variation with a rare-gas collision partner, due to the different interaction potentials. For sufficiently high collision energy, the branching approaches a recoil limit which is independent of collision partner.
We present a theoretical study of elastic and rotationally inelastic collisions of NH3 and ND3 with rare gas atoms (He, Ne, Ar, Kr, Xe) at low energy. Quantum close-coupling calculations have been performed for energies between 0.001 and 300 cm(-1). We focus on collisions in which NH3 is initially in the upper state of the inversion doublet with j = 1, k = 1, which is the most relevant in an experimental context as it can be trapped electrostatically and Stark-decelerated. We discuss the presence of resonances in the elastic and inelastic cross sections, as well as the trends in the inelastic cross sections along the rare gas series and the differences between NH3 and ND3 as a colliding partner. We also demonstrate the importance of explicitly taking into account the umbrella (inversion) motion of NH3 in order to obtain accurate scattering cross sections at low collision energy. Finally, we investigate the possibility of sympathetic cooling of ammonia using cold or ultracold rare gas atoms. We show that some systems exhibit a large ratio of elastic to inelastic cross sections in the cold regime, which is promising for sympathetic cooling experiments. The close-coupling calculations are based on previously reported ab initio potential energy surfaces for NH3-He and NH3-Ar, as well as on new, four-dimensional, potential energy surfaces for the interaction of ammonia with Ne, Kr, and Xe, which were computed using the coupled-cluster method and large basis sets. We compare the properties of the potential energy surfaces corresponding to the interaction of ammonia with the various rare gas atoms.
Coherence transfer accompanying 32P1/2 → 32P3/2 excitation transfer in sodium, induced in collisions with noble gas atoms, has been investigated using methods of sensitized fluorescence. Oriented 32P1/2 sodium atoms were produced by irradiating a mixture of sodium vapor and a noble gas with D1σ+ resonance radiation, and their subsequent collisions with the buffer gas atoms resulted in the simultaneous transfer of coherence and excitation from the 2P1/2 state to the 2P3/2 state. Measurements of the ratio of circular polarizations of the D2 sensitized fluorescence and D1 resonance fluorescence resulted in the following cross sections for coherence transfer. Na–He : 7.1 ± 0.7 Å2; Na–Ne : 6.2 ± 0.6 Å2; Na–Ar : 12.0 ± 1.2 Å2; Na–Kr : 6.8 ± 0.7 Å2; Na–Xe : 6.9 ± 0.7 Å2.
The cross sections for disorientation of 32P1/2 sodium atoms, induced in collisions with noble gas atoms, have been determined by following the depolarization of Na–D1 resonance fluorescence in relation to noble gas pressure. Sodium vapor at low density, mixed with a noble gas in a fluorescence cell, was irradiated with circularly polarized D1 resonance radiation and the resulting D1 resonance fluorescence, observed in an approximately backward direction, was analyzed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a 'J randomization' model for the collisions, and yielded the following disorientation cross sections which are appropriately corrected for effects due to nuclear spin. Na–He: 28.1 ± 4.0 Å2; Na–Ne: 27.8 ± 4.0 Å2; Na–Ar: 57.0 ± 8.0 Å2; Na–Kr: 78.0 ± 10 Å2; Na–Xe: 87.0 ± 13 Å2.