15min:
ANOMALOUS Lambda-DOUBLING IN THE INFRARED SPECTRUM OF THE HYDROXYL RADICAL IN HELIUM NANODROPLETS.

P. RASTON, T. LIANG AND G. E. DOUBERLY, Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.

The X 2 Pi3/2 hydroxyl (OH) radical has been isolated in superfluid 4He nanodroplets and probed with infrared laser depletion spectroscopy. From an analysis of the Stark spectrum of the Q (3/2) transition, the Lambda-doublet splittings are determined to be 0.198(3) cm-1 and 0.369(2) cm-1 in the ground and first excited vibrational states, respectively. These splittings are 3.6 and 7.2 times larger than their respective gas phase values. A factor of 1.6 increase in the Q (1/2) Lambda-doublet splitting was previously reported for the helium solvated X 2 Pi1/2 NO radical [K. von Haeften, A. Metzelthin, S. Rudolph, V. Staemmler, and M. Havenith, Phys. Rev. Lett. 95, 215301 (2005)]. A simple model is presented that predicts the observed Lambda-doublet splittings in helium solvated OH and NO. The model assumes a small parity dependence of the rotor's effective moment of inertia and predicts a factor of 3.6 increase in the OH ground state (J=3/2) Lambda-doubling when the B 0^ e and B 0^ f rotational constants differ by less than one percent.