Knowledge Bank

The optical spectrum of $NO2$ obtained in jet expansion fluorescence spectra by Persch et. al. [1], providing data on band origins shows a highly mixed spectrum with near-GOE level statistics, including level-repulsion. Microwave-detected microwave optical double resonance data obtained in our work [2], providing data on the distribution of levels at higher angular momentum, shows an ergodic spectrum with no detectable level repulsion. We examine the two data sets in the light of a multiple bright state model [3], and a related K-breakdown or weak-breakdown model. We find that the band origin data is consistent with a multiple bright state model with approximatley 4 bright states mixed into each observed state. The high J data is consistent with the K-breakdown model in which Coriolis-coupling matrix elements are much smaller than the bright state - dark state vibronic interaction. An experimental test of this model is proposed. This indicates that the presence of approximately conserved quantum numbers in a molecular spectrum complicates the application of statistical measures of ergodicity.