STRUCTURE AND VANDERWAALS VIBRATIONAL FREQUENCIES OF THE GLYOXAL . AR2 COMPLEX STUDIED BY FLUORESCENCE EXCITATION AND STIMULATED-EMISSION SPECTROSCOPY

Band-contour analysis of the fluorescence-excitation spectrum of the glyoxal. Ar2 complex permits the determination of its structure. The two Ar atoms are found to be at the same side of the glyoxal plane 3.5 A apart, and they occupy sites with a C2 symmetry and undergo large-amplitude zero-point motion. Many van der Waals vibrationallevels in the electronic ground state are detected by using stimulated-emission spectroscopy. A pair-potential model, with parameters taken from previous studies of Ar-Ar, Ar-CO, and Ar-H interactions, is used to calculate a structure that resembles that from spectralanalysis. However, a normal-mode analysis based on this potential was only partially successful in predicting the energy and providing the assignment for the van der Waals vibrational levels. The significance of the electronic and vibrational band shifts and the difference between the A- and X-state structures are also discussed. © 1990 Optical Society of America.