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 employe d to investigate rovibronic states of jet-cooled NO2 in the region of the d issociation threshold E-0. The method allows for the selection of angular m omenta 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 1 0 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 d issociation rate constants of 2 x 10(10) s(-1) and 1.65 x 10(10) s(-1), res pectively. 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 t o be small. The appearance of the double-resonance spectra does not princip ally 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-experime nts very close to the dissociation threshold is only weak and hardly detect able, which appears to be consistent with recent measurements in the time d omain. (C) 2001 American Institute of Physics.