Isotopic effects in HD$^+$ collision-induced dissociation*

Collision-induced dissociation (CID) of few keV HD$^+$ on an Ar target atom results from either electronic excitation to a dissociative state or a ro-vibrational excitation into the continuum of the electronic ground state, with the latter mechanism typically occurring in close-encounter collisions. We probe for a preferred channel (isotopic effect) in the dissociation of HD$^+$ into either H$^+$+D or H+D$^+$ final products. Preliminary results indicate that H+D$^+$ is somewhat favored over H$^+$+D when vibrational excitation drives the breakup. Existing theory $\left[1\right]$ predicts a factor of four preference in the branching ratio favoring H+D$^+$ in head-on collisions. Our experiment, using a coincidence 3D momentum imaging technique, enables the measurement of this branching ratio as a function of the scattering angle, i.e. the collision distance. Recent modifications to this experimental setup will improve the quality of the CID data, in particular for the ro-vibrational excitation mechanism of interest in this work\\[4pt] [1] D. Rapp, J. Chem. Phys. \textbf{32}, 735 (1960)