15min:
ROTATIONALLY RESOLVED ELECTRONIC SPECTRUM OF THE PARA-DIFLUOROBENZENE-NITROGEN VAN DER WAALS COMPLEX: STRUCTURE AND INTERNAL MOTION.

CHEOLHWA KANG AND DAVID W. PRATT, Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260; MARTIN SCHÄFER, Laboratorium für Physikalische Chemie, Eidgenössische Technische Höchschule Zürich, Zürich, ETH Hönggerberg - HCI, CH-8093 Zürich, Switzerland.

The rotationally resolved S1 leftarrow S0 fluorescence excitation spectra of p-difluorobenzene and its N2 complex have been observed. While the spectrum of pDFB is pure b-type, the spectrum of the N2 complex is a superposition of two pure c-type spectra that result from the internal rotation of the N2 molecule. The analysis reveals that N2 molecule lies above the center of the ring plane in the S0 state; this distance decreases in the S1 state. The preferred orientation and barrier to internal rotation in the two electronic states are also different. A full discussion of the factors responsible for the differences will be given.