5314027765

POSTER SESSION, H19

VIBRATIONALLY EXCITED STATES IN A PULSED JET OB-SERVED BY FOURIER TRANSFORM MICROWAVE SPEC-TROSCOPY

MARTIN SCHAFER and ALFRED BAUDER. Laboratorium fur Physikalische Chemie, ETH Zentrum, CH-8092 Ziinc.h, Switzerland.

The tec.hnique of pulsed 8 u personie molecular beam spectroscopy simplific^s rotational spectra because higher energy levels are depopulated during the expansion process, while in a static gas, the spectrum may be very dense due to the observation of numerous rotational transitions within different vibrational States.

While measuring Van der Waals complexes of fluorobenzene using a pulsed-jet Fourier transform cavity microwave spectrom eter, we observed jrotational transitions of several vibrationally excited States of fluorobenzene. The same transitions could also be observed with a waveguide Fourier transform microwave spectrometer in a static gas at room temperaturę, thus showing that these vibrationally excited States are only partially depopulated during the expansion. The influence of the kind of carrier gas and the stagnation pressure on the intensity of these lines will be discussed.