Polarized absorption spectroscopy of Λ-doublet molecules: Transition moment vs electron density distribution

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Abstract
Polarized two-photon photodissociation of NO2 in the region of 480 nm yields NO(v″=0) with an anisotropic distribution of J. Measured polarization ratios are compared to quantum mechanical calculations for a range of expected ratios for the various isolated and mixed branches of the NO X̃2Π1/2→Ã 2Σ+ transition. Theoretical results show that main branches and their respective satellites (e.g., R11 and R21 branches) have the same transition moment directionally, though their intensities are in general different, implying that care is needed in interpreting polarization data from the mixed branches, such as (Q21+R11) or (Q11+P21), which measure the Π+ and Π− Λ doublet, respectively. Recognition of this fact is particularly important for properly separating the consideration of electron density distributions of Λ doublets from transition moment directionalities, as this has been a source of confusion in the literature. The measured results indicate that the principal two-photon photoexcitation pathway in NO2 photolysis is 2A1→1 2B2→2 2B2, with moderate A″ state mixing in the intermediate.