Please join us for an informal seminar sponsored by the Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics. (Complete schedule at http://www.cfa.harvard.edu/amp/events.html) 11:00 AM Wednesday, June 13, 2012 Phillips Auditorium 60 Garden St, Cambridge, MA Reactive scattering at 10 mK: Observation of orbiting resonances Ed Narevicius (Weizmann Institute of Science) There is a fundamental interest in observation and study of resonances in atom and molecule scattering. Resonances probe fine details of interaction potentials and dominate collision dynamics at low temperatures. Quasibound resonances states are formed in the continuum part of spectrum making them accessible to scattering experiments where collision energy can be tuned, similarly to detection of bound states by tuning the excitation frequency in spectroscopy measurements. We report the first observation of orbiting resonances in the Penning ionization reaction of argon and molecular hydrogen with metastable helium atoms. Our result is the first direct measurement of a sharp increase in the absolute reaction rate due to the formation of metastable collision complex by quantum tunneling. In our approach we were able to break the barrier of 1 K collision temperature by merging two fast supersonic beams. As a result the relative velocity vanishes in a moving frame of reference. We use the Zeeman effect on paramagnetic species in order guide them in a section of a curved magnetic quadrupole guide. At the quadrupole exit paramagnetic particles beam merges with another supersonic beam that travelled straight from a separate supersonic source. By varying the relative velocities we continuously tune collisional energies from 700 K down to 10 mK which allows us the observation of resonances at low temperatures. _______________________________________________ Aspuru-meetings-list mailing list Aspuru-meetings-list(a)lists.fas.harvard.edu https://lists.fas.harvard.edu/mailman/listinfo/aspuru-meetings-list