15min:

PAUL RASTON, TAO LIANG, STEVEN D. FLYNN, ALEXANDER M. MORRISON AND GARY E. DOUBERLY, Department of Chemistry, University of Georgia, Athens, GA 30602-2556.

The hydroxyl radical and its complex with acetylene have been characterized in superfluid helium nanodroplets by infrared depletion spectroscopy. For OH, two sharp Q(3/2) lines were observed, with a separation that is consistent with a fivefold increase in the parity (lambda type) doubling of the ² _3/2 state in helium droplets relative to the gas phase. This increase is rationalized in terms of the differences in the potential energy surfaces for He-OH(A') and He-OH(A''), which are most pronounced at around 90^o. Switching to the T-shaped OH-C₂H₂ complex, depletion signals corresponding to OH and CH stretching transitions were observed. The spectra reveal that the electronic angular momentum of OH in the complex is only partially quenched, and to a similar degree as observed in the gas phase^,. This indicates that the helium droplet environment does not significantly affect the electronic intermolecular interactions in OH-C₂H₂.