Stereodynamics of rotational quenching in cold molecular collisions*

Stereodynamics of cold molecular collisions is an emerging area in cold and ultracold chemistry. Recently, Zare’s group examined the rotational quenching of HD in cold collisions with H₂, D₂ and He by combining the co-expansion of the colliding species and preparation of HD alignment and orientation with Stark-induced Adiabatic Raman Passage (SARP), and addressed the stereodynamic control of the angular distribution of inelastically scattered HD near 1K. In this study, we examine the possibility of stereodynamic control of rotational quenching in a strongly interacting system HCl+H₂ in the cold energy regime. Using quantum scattering calculations on an accurate 6D potential energy surface, we show that robust control of collision outcome is possible even when multiple shape-resonances coexist in a narrow energy range, indicating that cold stereochemistry offers great promise for many molecules beyond simple systems. Also, for HD+He, we demonstrate that an interplay of resonances from an l=1 and l=2 partial waves governs collision outcome than a single l=2 partial wave attributed in the experiment.