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 E-0. 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 E-0, 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 x 10(10) s(-1) and 1.65 x 10(10) s(-1), respectively. The experimental results for J=0.5 and 1.5 axe 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 concluded that the dependence of the average lifetimes on J in the present low J-experiments very close to the dissociation threshold is only weak and hardly detectable, which appears to be consistent with recent measurements in the time domain. (C) 2001 American Institute of Physics.