## Abstract

Recent quantum calculations of rotationally inelastic collisions of NaK (A^{1}Σ^{+}) 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 d_{K}(j, j′), which are proportional to tensor cross sections σ_{K}(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 d_{K} for certain transitions. Finally, several strategies for obtaining the d_{K} coefficients from experimental data are discussed.

Original language | English (US) |
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Article number | 074105 |

Journal | Journal of Chemical Physics |

Volume | 148 |

Issue number | 7 |

DOIs | |

State | Published - Feb 21 2018 |

## All Science Journal Classification (ASJC) codes

- General Physics and Astronomy
- Physical and Theoretical Chemistry