Photoassociative Excitation Spectroscopy of Excimer Molecules

Laser excitation spectroscopy of transitions having dissociative ground states was explored as a tool for the study of excimer molecules. Since the repulsive nature of the ground state constrains collision pairs to large internuclear transitions, bound >=ts free excitation spectra contain more structure than the bound to free fluorescence spectra for the same molecules, therefore containing more information about the potential surfaces. Unique properties of the photoassociative excitation spectroscopy technique are described which allow the dependence of the dipole transition moment on the internuclear separation (mu (R)) to be extracted in a very direct manner. Excitation spectra are presented for the B >=ts X transitions of KrF and XeI for the wavelength (lambda) interval 206 nm < lambda < 255 nm. The excitation spectra are analyzed using an iterative trial and error comparison with calculated spectra. The effect of the rotational potential is examined. Potential surfaces and the mu(R) results are given for both molecules. The possible use of the technique is then discussed for excimer molecules having predissociative upper states. Some preliminary results for KrI are given. This work required the development of a tunable VUV source, which is described.