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MO: Molekülphysik

MO 13: Spektroskopie III

MO 13.1: Vortrag

Donnerstag, 19. März 1998, 14:00–14:15, M629

Studies of NO2 by LIF and bolometric detection — •S. Stolte, C.A. Biesheuvel, J. Bulthuis, and M.H.M. Janssen — Dept. of Chemistry, Laser Centre, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, Netherlands

The first visible absorption spectrum of NO2 was measured by Brewster in 1834. It took more than hundred years before the first rotational analysis of a part of the visible absorption spectrum was reported. The vibrational structure of the visible/near-infrared absorption spectrum is dominated by a strong conical intersection between the potential energy surfaces of the electronic ground state and of the first electronically excited state. As a result the visible absorption spectrum of NO2 is dense, complex and irregular. It suggest the presence of a ’quantum’ chaos in the distribution of vibronic origins in the 16000 cm-1 to 25000 cm -1 range. We have to set out to directly investigate the region just above the conical intersection by exciting a supersonically cooled beam of a photomultiplier or a bolometer. In this manner we can resolve the lines up to the hyperfine structure, which gives information about the interaction of vibrational states of the first electronically excited state 2B2 (almost zero hyperfine splitting) and the highly excited vibrational states of the electronic ground state 2A1 (with a significantly larger hyperfine splitting) in that particular vibronic band. In the energy range of 11000 cm-1 to 13700-1 the hfs splittings and intensity distribution appear regular and reflect the fraction of 2A1 character(30-80%).