Stereodynamics of D₂ (<i>v</i> = 2, <i>j</i> = 2) → D₂ (<i>v</i> = 2, <i>j</i> = 0) cold collision with He reveals resonance

By preparing D₂ in the rovibrational eigenstate (v = 2, j = 2) with three different bond axis orientations using Stark-induced adiabatic Raman passage (SARP), we study the stereodynamics of rotational relaxation of D₂ (v = 2, j = 2) → D₂ (v = 2, j = 0) via collision with ground-state He. The collision temperature is cooled to a few degrees Kelvin by coexpanding the colliding partners in a single supersonic beam, thus limiting the input orbital states to l = 0, 1, 2. Specifically, the D₂ bond axis is prepared either parallel, perpendicular, or in a coherent superposition of two orientations at 45° with respect to the collision velocity. We observed marked stereodynamic features for each orientation of the D₂ bond axis. Partial wave analysis of the rotationally relaxed D₂ (v = 2, j = 0) angular distribution shows dominance of the even outgoing orbitals l′ = 0, 2, 4, which strongly suggests a scattering resonance for the l = 2 input orbital. The l = 2 resonance is further supported by comparing the collision temperature distribution with the centrifugal barrier.