LASER SPECTROSCOPY OF HG-2 EXCIMERS

Molecular fluorescence of mercury has been known for over 60 years, an d some of the important early experiments were carried out and interpr eted in the 1930s at the University of Warsaw in Poland. It was not un til the mid 1970s, that the continuum bands, emitted from excited merc ury vapour, were properly assigned to the lowest electronic states of the Hg-2 and Hg-3 molecules. Comprehensive and quantitative informatio n on the higher states of the Hg-2 excimer has only become available d uring the past 15 years, largely as the result of flash photolysis exp eriments carried out in Cambridge, and our own studies of laser-induce d fluorescence with time-resolution. We now report on our recent exper iments, in which we used pump-and-probe methods to produce rotationall y resolved excitation spectra of monoisotopic (Hg-202)(2). The rotatio nal analyses of the observed structures yielded very accurate values o f spectroscopic constants, and permitted some meaningful comparisons w ith ''ab-initio'' calculations of potential-energy diagrams.