Differential scattering of cold molecules in external electric and magnetic fields

Previous work has shown that integral cross sections for molecular collisions at low temperatures can be controlled by external electromagnetic fields [1]. Here, we demonstrate that the differential scattering cross sections (DCS) may also be sensitive to external fields. The DCS is a coherent superposition of different partial wave ($\ell$) contributions. Electric fields mix different rotational states, which leads to an indirect coupling of states with different $\ell$, and modifies the angular dependence of the DCS. We show that the DCS for spin depolarization in CaH($^2\Sigma$)--He collisions can be shifted from sideways-peaked (in the absence of an electric field) to forward-peaked (at electric fields of $\sim100$ kV/cm). This can be used to obtain valuable information about the anisotropy of intermolecular interactions [2], design experiments for kinematic slowing of molecules via inelastic collisions [1], and explore the stereodynamics of molecular collisions and chemical reactions~[3]. References: [1]~R.~V.~Krems, Int. Rev. Phys. Chem. {\bf 24}, 99 (2005); [2] U. Buck, Rev. Mod. Phys. {\bf 46}, 369 (1974); [3] D.~Herschbach, Eur. Phys. J. D {\bf 38}, 3 (2006).