Physical Review Letters

Nonadiabatic Coupling in Fine-Structure Transitions of Alkali Atoms Induced by Diatomic Molecules

A. P. Hickman

Published Nov 30, 1981• 17 citations

Abstract

Fine-structure transitions of alkali atoms induced by collisions with diatomic molecules are shown to be strongly influenced by a dynamical feature that is completely absent when the collision partner is a rare gas. The effect is a nonadiabatic coupling caused by the anisotropy of the molecule. Calculations for $\mathrm{Rb}(5^{2}P_{\frac{1}{2}})$ + ${\mathrm{H}}_{2}$ and for $\mathrm{Rb}(5^{2}P_{\frac{1}{2}})$ + He are in good agreement with recent experiments and explain the dramatic difference between these two systems.

DOI: 10.1103/physrevlett.47.1585

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Theory of excitation transfer in collisions between alkali atoms. I. Identical partners

E. I. Dashevskaya, A. Voronin, E. E. Nikitin

A mechanism is derived for nonresonant transfer of electronic excitation energy, induced in the process M*(2P3/2) + M(2S1/2) → M*(2P1/2) + M(2S1/2), where M and M* are identical alkali atoms in the ground and first excited states, respectively. Various types of interactions, responsible for the nonadiabatic combination of electronic states of the quasi molecule M2*, were considered, and their respective contributions to the cross section for excitation transfer were determined.

Canadian Journal of PhysicsJun 15, 196978 citations

Physical Review Letters

Nonadiabatic Coupling in Fine-Structure Transitions of Alkali Atoms Induced by Diatomic Molecules

A. P. Hickman

Published Nov 30, 1981• 17 citations

Publisher

Abstract

\mathrm{Rb}(5^{2}P_{\frac{1}{2}})

{\mathrm{H}}_{2}

and for

\mathrm{Rb}(5^{2}P_{\frac{1}{2}})

+ He are in good agreement with recent experiments and explain the dramatic difference between these two systems.

DOI: 10.1103/physrevlett.47.1585

Related papers

The role of adiabaticity in alkali atom-fine structure mixing

Ben Eshel, David E. Weeks, Glen P. Perram

Fine-structure mixing cross-sections for the alkalis in collisions with the rare gases are reviewed. Included in the review are all the rare gases in collisions with all of the first excited state of the alkalis, the second excited state for K, Rb and Cs and the third excited state for Rb and Cs. The cross-sections are converted to probabilities for energy transfer using a quantum-defect calculated cross-section and are then presented as a function of adiabaticity. The data shows a clear decreasing trend with adiabaticity but secondary factors prevent the probabilities from decreasing as quickly as expected. Polarizability is introduced as a proxy for the secondary influences on the data as it increases with both rare gas partner and alkali excited state. The polarizability is shown to cause the probability of fine structure transition to be higher than expected. An empirical model is introduced and fit to the data. Future work will develop a model using time-independent perturbation theory in order to further develop a physical rational for the dependence of fine structure cross sections on adiabaticity and to further understand the secondary influences on the probability for fine structure transition.Fine-structure mixing cross-sections for the alkalis in collisions with the rare gases are reviewed. Included in the review are all the rare gases in collisions with all of the first excited state of the alkalis, the second excited state for K, Rb and Cs and the third excited state for Rb and Cs. The cross-sections are converted to probabilities for energy transfer using a quantum-defect calculated cross-section and are then presented as a function of adiabaticity. The data shows a clear decreasing trend with adiabaticity but secondary factors prevent the probabilities from decreasing as quickly as expected. Polarizability is introduced as a proxy for the secondary influences on the data as it increases with both rare gas partner and alkali excited state. The polarizability is shown to cause the probability of fine structure transition to be higher than expected. An empirical model is introduced and fit to the data. Future work will develop a model using time-independent perturbation theory in order to further develop a physical rational for the dependence of fine structure cross sections on adiabaticity and to further understand the secondary influences on the probability for fine structure transition.

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A theoretical model is presented for the interaction between an alkali atom in the first excited 2 P state and a ground state rare gas atom, which is effective in causing transitions among the alkali fine structure states. The main difference from previously used models is a more detailed treatment of short range effects including deviations from straight line paths in the semiclassical treatment. An application to the case of Rb interacting with He, Ne, Ar, and Kr gives results for the depolarization and inelastic cross sections which are in reasonable accord with experiment.A theoretical model is presented for the interaction between an alkali atom in the first excited 2 P state and a ground state rare gas atom, which is effective in causing transitions among the alkali fine structure states. The main difference from previously used models is a more detailed treatment of short range effects including deviations from straight line paths in the semiclassical treatment. An application to the case of Rb interacting with He, Ne, Ar, and Kr gives results for the depolarization and inelastic cross sections which are in reasonable accord with experiment.

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Role of adiabaticity in controlling alkali-metal fine-structure mixing induced by rare gases

Ben Eshel, Joseph A. Cardoza, David E. Weeks +1 more

The collision cross sections for alkali-metal--rare-gas spin orbit mixing between the ${n}^{2}{P}_{3/2}\ensuremath{\rightarrow}{n}^{2}{P}_{1/2}$ levels trend strongly with the Massey parameter, or adiabaticity of the collisions. The strength of the interaction, as characterized by the ${C}_{6}$ dispersion coefficient, is a secondary influence on the rates. An analytic expression for the probability of energy transfer in alkali-metal--rare-gas collisions is derived using time-dependent perturbation theory. The model agrees well with a broad literature survey of the observed temperature-dependent cross sections. A simple interaction potential successfully organizes the alkali-metal--rare-gas database. The rates become very large for high-lying states, as the collisions are quite sudden and the radius of the valence electron is large. In contrast, the highly adiabatic cesium ${6}^{2}P$ mixing rates are six to eight orders of magnitude smaller. The mixing rate for the Rb-He diode pumped alkali laser system varies from $0.20--1.53\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{cm}{}^{3}/\mathrm{at}.\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ for $T=279--893\phantom{\rule{0.222222em}{0ex}}\mathrm{K}$ .The collision cross sections for alkali-metal--rare-gas spin orbit mixing between the ${n}^{2}{P}_{3/2}\ensuremath{\rightarrow}{n}^{2}{P}_{1/2}$ levels trend strongly with the Massey parameter, or adiabaticity of the collisions. The strength of the interaction, as characterized by the ${C}_{6}$ dispersion coefficient, is a secondary influence on the rates. An analytic expression for the probability of energy transfer in alkali-metal--rare-gas collisions is derived using time-dependent perturbation theory. The model agrees well with a broad literature survey of the observed temperature-dependent cross sections. A simple interaction potential successfully organizes the alkali-metal--rare-gas database. The rates become very large for high-lying states, as the collisions are quite sudden and the radius of the valence electron is large. In contrast, the highly adiabatic cesium ${6}^{2}P$ mixing rates are six to eight orders of magnitude smaller. The mixing rate for the Rb-He diode pumped alkali laser system varies from $0.20--1.53\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{cm}{}^{3}/\mathrm{at}.\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ for $T=279--893\phantom{\rule{0.222222em}{0ex}}\mathrm{K}$.

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Mariusz Pawlak, Yuval Shagam, Ayelet Klein +2 more

We recently developed an adiabatic theory for cold molecular collision experiments. In our previous application of this theory (Pawlak, M.; et al. J. Chem. Phys. 2015, 143, 074114), we assumed that during the experiment the collision of an atom with a diatom takes place when the diatom is in the ground rotational state and is located in a plane. In this paper, we present how the variational approach of the adiabatic theory for low-temperature collision experiments can be used for the study a 5D collision between the atom and the diatomic molecule with no limitations on its rotational quantum states and no plane restrictions. Moreover, we show here the dramatic differences in the measured reaction rates of He(2 3 S 1 ) + ortho / para -H 2 → He(1s 2 ) + ortho / para -H 2 + + e – resulting from the anisotropic long-range interactions in the reaction. In collisions of metastable helium with molecular hydrogen in the ground rotational state, the isotropic potential term dominates the dynamics. When the collision is with molecular hydrogen in the first excited rotational state, the nonisotropic interactions play an important role in the dynamics. The agreement of our results with the latest experimental findings ( Klein, A.; et al. Nat. Phys. 2017, 13, 35−38) is very good.We recently developed an adiabatic theory for cold molecular collision experiments. In our previous application of this theory (Pawlak, M.; et al. J. Chem. Phys. 2015, 143, 074114), we assumed that during the experiment the collision of an atom with a diatom takes place when the diatom is in the ground rotational state and is located in a plane. In this paper, we present how the variational approach of the adiabatic theory for low-temperature collision experiments can be used for the study a 5D collision between the atom and the diatomic molecule with no limitations on its rotational quantum states and no plane restrictions. Moreover, we show here the dramatic differences in the measured reaction rates of He(2 3 S 1 ) + ortho / para -H 2 → He(1s 2 ) + ortho / para -H 2 + + e – resulting from the anisotropic long-range interactions in the reaction. In collisions of metastable helium with molecular hydrogen in the ground rotational state, the isotropic potential term dominates the dynamics. When the collision is with molecular hydrogen in the first excited rotational state, the nonisotropic interactions play an important role in the dynamics. The agreement of our results with the latest experimental findings ( Klein, A.; et al. Nat. Phys. 2017, 13, 35−38) is very good.

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Nonadiabatic theory of fine-structure branching cross sections for Na-He, Na-Ne, and Na-Ar optical collisions

Linda L. Vahala, Paul S. Julienne, Mark D. Havey

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 ${(}^{2}$ ${S}_{1/2}$ )+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na ${(}^{2}$ ${\mathrm{P}}_{\mathrm{j}}$ )+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3 ${p}^{2}$ ${P}_{3/2}$ and 3p $^{2}P_{1/2}$ 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.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}$${S}_{1/2}$)+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na${(}^{2}$${\mathrm{P}}_{\mathrm{j}}$)+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3${p}^{2}$${P}_{3/2}$ and 3p $^{2}P_{1/2}$ 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.

Physical Review ASep 1, 198641 citations

Theory of excitation transfer in collisions between alkali atoms. I. Identical partners

E. I. Dashevskaya, A. Voronin, E. E. Nikitin

Canadian Journal of PhysicsJun 15, 196978 citations

\mathrm{Rb}(5^{2}P_{\frac{1}{2}})

{\mathrm{H}}_{2}

and for

\mathrm{Rb}(5^{2}P_{\frac{1}{2}})

+ He are in good agreement with recent experiments and explain the dramatic difference between these two systems.

{C}_{6}

dispersion coefficient, is a secondary influence on the rates. An analytic expression for the probability of energy transfer in alkali-metal--rare-gas collisions is derived using time-dependent perturbation theory. The model agrees well with a broad literature survey of the observed temperature-dependent cross sections. A simple interaction potential successfully organizes the alkali-metal--rare-gas database. The rates become very large for high-lying states, as the collisions are quite sudden and the radius of the valence electron is large. In contrast, the highly adiabatic cesium

{6}^{2}P

mixing rates are six to eight orders of magnitude smaller. The mixing rate for the Rb-He diode pumped alkali laser system varies from $0.20--1.53\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{cm}{}^{3}/\mathrm{at}.\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ for

T=279--893\phantom{\rule{0.222222em}{0ex}}\mathrm{K}

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}

{S}_{1/2}

)+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na

{(}^{2}

{\mathrm{P}}_{\mathrm{j}}

)+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3

{p}^{2}

{P}_{3/2}

and 3p

^{2}P_{1/2}

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.