Highly excited states of nitric oxide studied by two-color double resonance spectroscopy

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Abstract
Double resonance enhanced four-photon ionization spectra and fluorescence dip spectra of nitric oxide have been simultaneously measured using two tunable dye lasers. The spectra showed clear rovibronic structure of the 2Σ+ and 2Π states in the third-photon region (65 000∼70 000 cm−1). Laser power dependencies of the fluorescence dip and the ionization signals have been analyzed by kinetic rate equations and the absorption cross section of the transition between the second resonance state and the A 2Σ+ state has been obtained. Finally, by varying the delay time between the pulses from the first and second dye lasers, we have observed collision induced rotational relaxation in the A 2Σ+ state. The relaxation rate was found to be comparable to the electronic quenching rate.