High resolution spectroscopy of radical complexes in the visible and ultraviolet regions, and determination of their intermolecular potentials

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The present research project intended to study radical complexes by means of a laser induced fluorescence spectroscopic technique using a Nd-YAG pumped tunable dye laser system combined with a pulsed-discharge-nozzle. Especially, by utilizing a frequency doubled dye laser we were able to observe LIF spectra of a rare gas-OH complex in the near UV region, which has been studied extensively. We have produced the OH radical in the supersonic jet by discharging water diluted in Ar.Spectra of Ar-OH were observed with a good signal to noise ratio between much stronger OH monomer lines, by carefully adjusting the nozzle dimensions and discharge conditions. Since we have confirmed that our system is capable to observe LIF spectra of a radical complex, we have started to search a new system by discharging various parent molecules diluted in rare gases. So far, we were able to observe monomer radicals C_2, C_3, CN,CCN etc. fairly strongly, and are continuing the search for spectra of complexes containing these short lived radical species.Along with these experimental studies, we have developed a program system to analyze the large amplitude motion of the radical complexs, where energy levels are far more complicated than those of complexes with closed shell molecules, since the radicals usually have an unpaired electron and its spin and/or orbital angular momenta couple with the large amplitude motion. We were able to explain the observed spectral patterns in the case of the rare gas-OH complexes. Especially, we have accurately treated the hyperfine interaction under the large amplitude motion, and have shown that it is possible to derive information for the intermoleclular potential from the observed hyperfine patterns.