Stereodynamics of rotationally inelastic scattering in cold He+HD collisions.

Stereodynamics of cold collisions has become a fertile ground for quantized studies of molecular collisions and control of the collision outcome. A benchmark process for stereodynamic control is rotational transition in He+HD collisions. This process was recently probed experimentally by Perreault et al. by examining quenching from $j=2$ to $j'=0$ state in the $v=1$ vibrational manifold. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He+H$_2$, we reveal how a combination of two shape resonances arising from $l=1$ and $l=2$ partial waves controls the stereodynamic outcome rather than a single $l=2$ partial wave attributed in the experiment. Further, for collision energies below 0.5 cm$^{-1}$, it is shown that stereodynamic preference for integral cross section follows a simple universal trend.