PRODUCTION AND CHARACTERIZATION BY LASER SPECTROSCOPY OF FREE RADICALS, MOLECULAR IONS, AND ION CLUSTERS IN A FREE JET EXPANSION

Free radicals have been produced by excimer laser photolysis of parent molecules seeded in a free jet expansion in an inert gas. Laser induced fluorescence probing of the CN radical produced in this manner yields rotational temperatures from $\sim 4000K$ to $\leq 10K$. This technique clearly provides both a method for studying rotational and vibrational relaxation, as well as a source of ultra-cold free radicals. When fluorobenzene molecules are seeded in the jet, 2-photon photoionization produces the corresponding radical cations. Laser excitation spectra of ultra-cold bare cations and, in addition, ion clusters have been obtained and will be discussed