ELECTRONIC SPECTROSCOPY OF THE AROH AND AROD COMPLEXES

Laser induced fluorescence spectra of the ArOH bands associated with electronic excitation of the OH A-X(v′ = 0 - v″ = 0) transition were reported previously. An extensive search in the vicinity of the OH/OD A ( 2Σ+) - X(2Π) system (v′ = 0 - ″ = 0 and v′ = 1 - v″ = 0) led to the observation of 36 vibronic bands which were identified as belonging to ArOH or ArOD complexes. All of the bands were found to originate from the 2Π(3/2) , v″ = 0 ground electronic state of the OH/OD radical. Two distinguishable vibronic structures were identified. A lower energy vibrational progression was assigned to the van der Waals stretch. This band system was designated as the "A" bands. A higher energy set of bands exhibited a different vibrational structure which did not fit a simple vibrational mode progression. These bands were labeled as the "U" system. Spectra showing partially resolved rotational structure were recorded for all of the observed ArOH/ArOD bands. The A and U systems were also distinguished by differences in their rotational structure and effects of H/D substitution on the vibrational and rotational parameters. Preliminary rotational analysis gave ground state constants (B″0) of 0.100 cm-1 for ArOH and 0.098 cm-1 for ArOD. (B′e, constants for the excited state of the A system were determined to be 0.178 cm-1 for ArOH and 0.168 cm-1 for ArOD. These rotational constants show that the Ar-OH/Ar-OD van der Waals bond has been considerably shortened upon electronic excitation. This suggests that partial charge transfer might contribute to the stability of ArOH and ArOD complexes in the excited electronic state. Observed spectra and results of rovibronic analysis are discussed. © 1990 American Institute of Physics.