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Price TJ, Hickman AP. Semiclassical analysis of jm → j'm' transitions in rotationally inelastic collisions in cell experiments. J Chem Phys 2018; 148:074105. [PMID: 29471636 DOI: 10.1063/1.4996877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Recent quantum calculations of rotationally inelastic collisions of NaK (A1Σ+) with He or Ar in a cell experiment are analyzed using semiclassical approximations valid for large quantum numbers. The results suggest a physical interpretation of jm → j'm' transitions based on the vector model and lead to expressions that explicitly involve the initial and final polar angles of the angular momentum of the target molecule. The relation between the polar angle θ and the azimuthal quantum number m links the semiclassical results for the change in polar angle (θ → θ') to quantum results for an m → m' transition. Analytic formulas are derived that relate the location and width of peaks in the final polar angle distribution (PAD) to the K-dependence of the coefficients dK(j, j'), which are proportional to tensor cross sections σK(j → j'). Several special cases are treated that lead to final PADs that are approximately Lorentzian or sinc functions centered at θ' = θ. Another interesting case, "angular momentum reversal," was observed in the calculations for He. This phenomenon, which involves a reversal of the direction of the target's angular momentum, is shown to be associated with oscillatory behavior of the dK for certain transitions. Finally, several strategies for obtaining the dK coefficients from experimental data are discussed.
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Affiliation(s)
- T J Price
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - A P Hickman
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
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Jones J, Richter K, Price TJ, Ross AJ, Crozet P, Faust C, Malenda RF, Carlus S, Hickman AP, Huennekens J. Rotationally inelastic collisions of excited NaK and NaCs molecules with noble gas and alkali atom perturbers. J Chem Phys 2017; 147:144303. [PMID: 29031279 DOI: 10.1063/1.4997577] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report measurements of rate coefficients at T ≈ 600 K for rotationally inelastic collisions of NaK molecules in the 2(A)1Σ+ electronic state with helium, argon, and potassium atom perturbers. Several initial rotational levels J between 14 and 44 were investigated. Collisions involving molecules in low-lying vibrational levels (v = 0, 1, and 2) of the 2(A)1Σ+ state were studied using Fourier-transform spectroscopy. Collisions involving molecules in a higher vibrational level, v = 16, were studied using pump/probe, optical-optical double resonance spectroscopy. In addition, polarization spectroscopy measurements were carried out to study the transfer of orientation in these collisions. Many, but not all, of the measurements were carried out in the "single-collision regime" where more than one collision is unlikely to occur within the lifetime of the excited molecule. The analysis of the experimental data, which is described in detail, includes an estimate of effects of multiple collisions on the reported rate coefficients. The most significant result of these experiments is the observation of a strong propensity for ΔJ = even transitions in collisions involving either helium or argon atoms; the propensity is much stronger for helium than for argon. For the initial rotational levels studied experimentally, almost all initial orientation is preserved in collisions of NaK 2(A)1Σ+ molecules with helium. Roughly between 1/3 and 2/3 of the orientation is preserved in collisions with argon, and almost all orientation is destroyed in collisions with potassium atoms. Complementary measurements on rotationally inelastic collisions of NaCs 2(A)1Σ+ with argon do not show a ΔJ = even propensity. The experimental results are compared with new theoretical calculations of collisions of NaK 2(A)1Σ+ with helium and argon. The calculations are in good agreement with the absolute magnitudes of the experimentally determined rate coefficients and accurately reproduce the very strong propensity for ΔJ = even transitions in helium collisions and the less strong propensity for ΔJ = even transitions in argon collisions. The calculations also show that collisions with helium are less likely to destroy orientation than collisions with argon, in agreement with the experimental results.
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Affiliation(s)
- J Jones
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - K Richter
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - T J Price
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - A J Ross
- Institut Lumière Matiere, UMR 5306 Université Lyon I-CNRS, Université de Lyon, 69622 Villeurbanne, France
| | - P Crozet
- Institut Lumière Matiere, UMR 5306 Université Lyon I-CNRS, Université de Lyon, 69622 Villeurbanne, France
| | - C Faust
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - R F Malenda
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - S Carlus
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - A P Hickman
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
| | - J Huennekens
- Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, Pennsylvania 18015, USA
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Price T, Towne A, Talbi D, Hickman A. Semiclassical model for the distribution of final polar angles and m′ states in rotationally inelastic collisions. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2015.12.037] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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