			15min:

FIRST MICROWAVE SPECTRA IN DOPED HELIUM CLUSTERS.

I. REINHARD, C. CALLEGARI, K. K. LEHMANN AND G. SCOLES, Department of Chemistry, Princeton University, Princeton, NJ 08544.

In the framework of the investigation of the relaxation mechanisms of molecular rotational and vibrational excitations in a superfluid helium cluster environment, the first microwave absorption spectra have been obtained for He clusters doped with acetonitrile (CH₃CN). Two broad (~ 1\,GHz) peaks centered at about 12.5 and 15\,GHz have been observed using bolometric detection of the beam attenuation caused by successive absorption of several microwave photons in a 10\,cm long waveguide. The change in rotational constants induced by the presence of the medium preclude assignment based on a mere comparison with gas phase spectra. Further measurements are currently in progress to assign the observed features and determine the rotational relaxation times of the system.