Stereodynamics of cold and ultracold rotationally inelastic collisions

Stereodynamics of cold collisions has become a fertile ground for sensitive probe of molecular collisions and control of the collision outcome. A benchmark system for stereodynamic control of rotational transition is He + HD. This system was recently probed experimentally by Perreault et al. [1] by examining quenching from j = 2 to j'=0 state in the v = 1 vibrational manifold of HD by preparing the initial molecular  orientation as a coherent superposition of m_j states. Here we report explicit quantum calculations of rotational quenching of HD within the v=1 vibrational level by collisions with He for j=2 and 3 in the cold and ultracold regimes. In the cold regime near 1 K, the stereodynamics is controlled by the l=1 and l=2 partial waves [2,3]. While  stereodynamic control is generally not effective in the ultracold  regime due to the dominance of the incoming s-wave (l = 0 partial wave) we show strong m_j and m_j^' dependence for both integral and differential cross cross sections in the ultracold regime [3].

[1] W. E. Perreault, N. Mukherjee, and R. N. Zare, J. Chem. Phys. 150, 174301 (2019).

[2] M. Morita and N. Balakrishnan, J. Chem. Phys. 153, 091101 (2020).

[3] M. Morita and N. Balakrishnan, J. Chem. Phys. 153, 184307 (2020).