Double resonance infrared–visible photofragment yield spectroscopy of NO2: Interferences among overlapping quasibound levels

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Abstract
We examine fluctuations in the unimolecular decomposition of state-selected NO2 using double resonance infrared (IR)–visible and visible–IR photofragment yield (PHOFRY) spectroscopy. Spectra for specific NO(v,J,Λ,Ω) states at excess energies (E°)=2000–2525 cm−1 exhibit marked differences in the shapes, positions, and widths of the resonance structures. We interpret this effect as arising from interferences among coherently excited overlapping quasibound levels. Comparisons of IR–visible PHOFRY spectra with one-photon spectra in the same energy region and IR–visible spectra at lower E° are used to assess the importance of thermal averaging (i.e., incoherent excitations) and to examine the transition from mild to more severe level overlap. The experimental results are compared qualitatively with results from sample calculations to shed further light on the interplay between dynamics and statistics in the decomposition and the role of overlapping quasibound levels.