Controlling the dynamics of cold molecular collisions

The dynamics of many chemical processes are determined by the relative orientation of colliding molecules. Here, we report results of quantum dynamics calculations for cold collisions of rotationally excited HD with H$_2$, and examine how the collisional dynamics can be controlled by varying the initial alignment of the HD. Such control over the alignment of colliding molecules is now experimentally possible using the SARP method. Taking rotational quenching rates as an example we show that the rate can be maximised by aligning the HD along the relative collision axis and minimised by aligning the HD at the so called magic angle.