Specific rate constants k(E,J) for the dissociation of NO2: II. Linewidths of rotationally selected NO2 near to the dissociation threshold.

Optical double-resonance “fluorescence depletion pumping,” has been employed to investigate rovibronic states of jet-cooled NO2 in the region of the dissociation threshold E0. The method allows for the selection of angular momenta of the reacting molecules. In particular, molecules with J=0.5 and 1.5 or with J=2.5 and 3.5 have been selectively investigated. In the first 10 cm−1 above E0, the linewidths for J=0.5 and 1.5 as well as 2.5 and 3.5 have been found to fluctuate around average values which correspond to dissociation rate constants of 2×1010 s−1 and 1.65×1010 s−1, respectively. The experimental results for J=0.5 and 1.5 are in agreement with time-resolved data and quantum mechanical calculations. The difference in average linewidths for the molecules with J=0.5/1.5 and 2.5/3.5 was found to be small. The appearance of the double-resonance spectra does not principally change for higher angular momentum J, i.e., some sharp lines on top of a congested unresolved background are still observed. It is co...