Mainz 2017 – scientific programme
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MO: Fachverband Molekülphysik
MO 2: Precision Experiments on Small Molecules
MO 2.4: Talk
Monday, March 6, 2017, 15:15–15:30, N 25
Experimental studies of the ion-molecule reactions H2++H2 and H2++D2 at low collision energies with a merged beam apparatus — •Katharina Höveler, Pitt Allmendinger, Johannes Deiglmayr, Otto Schullian, and Frédéric Merkt — Laboratorium für Physikalische Chemie, ETH Zürich, CH-8093 Zurich, Switzerland
The exothermic, barrierless H2++H2 →H3++H reaction has been studied in the collision-energy range Ecoll / kb = 300 mK−50 K. To reach such low collision energies, we use a merged-beam approach and substitute the H2+ reactants by the ionic cores of H2 molecules in high-n Rydberg-Stark states. The Rydberg electron does not influence the reaction but shields the ion from heating by space-charge effects and stray electric fields. Merging of the two pulsed reactant supersonic beams is achieved by photoexcitation of the molecules of one beam to high-n Rydberg-Stark states followed by Rydberg-Stark deceleration and deflection using a curved chip-based surface-electrode device. The collision energy is tuned by varying the temperature of the valve generating the H2 ground-state beam for selected velocities of the H2 Rydberg beam. The reaction cross section is found to follow the classical Langevin capture model down to Ecoll / kb=5 K. At lower temperatures, a deviation is observed and attributed to ion-quadrupole long-range interactions. Investigation of the reaction H2++D2 enables us to distinguish between charge transfer, D atom transfer and H+ ion transfer.