Doppler-free infrared spectroscopy by opto-thermal detection

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The original project described in the proposal was to construct an apparatus for high-resolution spectroscopy utilizing a color-center laser, but became impracticable because of a fatal damage of the laser. Instead, we carried out the following high-resolution spectroscopic studies in line with the same purpose.First, we constructed an apparatus for high-resolution LIF spectroscopy. The apparatus was tested by the observation of the B - X band of the NeBr_2 van der Waals complex using a cell with a pulsed supersonic nozzle. It was further tested by the observation at a resolution of 0.028 cm^<-1> of the A^2Σ-X^2Π band of the OH radical using a cell with a pulsed discharge nozzle. We hope that this apparatus may be developed for application to double resonance spectroscopy in which microwave and cavity ringdown techniques are combined.Second, we have developed a new spectroscopic technique in which millimeter wave spectroscopy, pulsed supersonic jet, and excimer laser photolysis were co … More mbined. This technique was applied to observation of the spectrum of the vinyl radical. The in-plane CH bending vibration of this radical is governed by a double minimum potential, and the ground vibrational state is split into the "s" and "a" tunneling doublet. We observed tunneling-rotation transitions connecting the "s" and "a" states, as well as pure rotational transitions which occur within the "s" or "a" state. Precise knowledge on the double minimum potential, electron-spin-rotation interaction, electron-spin-nuclear-spin interactions.Third, we observed the high-resolution vibration-rotation spectrum of the CoCO radical by infrared diode laser spectroscopy combined with excimer laser photolysis. The fundamental band of the CO stretching (ν_1) vibration, and hot bands starting from excited states of the bending (ν_2) and CoO stretching (ν_3) vibrations. Precise knowledge was obtained on the equilibrium structure and others. It was confirmed that this radical has the ^2Δ_i, electronic ground state. Millimeter wave spectrum was also observed yielding precise hyperfine interaction constants of the Co nucleus. Less