Berlin 2014 – scientific programme

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MO: Fachverband Molekülphysik

MO 22: Cold Molecules 3

MO 22.2: Talk

Friday, March 21, 2014, 10:45–11:00, BEBEL SR144

Ne* + NH3: Polyatomic Chemical Reactions in the Low-Temperature Regime — •Justin Jankunas, Benjamin Bertsche, and Andreas Osterwalder — Ecole Polytechnique Federale de Lausanne

A novel merged beam (MB) technique for neutral molecules has been employed to study bimolecular collisions between electronically excited neon atoms and supersonically cooled ammonia molecules. Cross sections of the two reaction channels, namely Ne* + NH3 * Ne + NH3+ + e- and Ne* + NH3 * Ne + NH2+ + H + e-, have been measured as a function of relative velocity between Ne* and NH3. The lowest and highest collision energies achieved are 0.1 K (8 μeV) and 250 K (0.22 meV), respectively. We find that the cross section for the two reaction channels increases upon lowering the collision energy. The long range forces dominate the outcome of a reaction in the 0.1 K to ~ 10 K temperature range. The role played by short-ranged chemical forces becomes apparent when the collision energy is greater than ~ 10 K. We have also measured the ratio, Γ = NH2+ / (NH2+ + NH3+), of the two reaction channels. Surprisingly, the ratio is constant (Γ ~ 0.3) in the collision energy range studied, defying our naïve expectation that as the collision energy vanishes, a channel with a lower minimum energy path dominates the reaction. We suggest that similar effects may be present in other electron transfer reactions.