Nanosecond time-resolved IR emission from molecules excited in a supersonic jet:: Intramolecular dynamics of NO2 near dissociation -: art. no. 154306

IR emission from NO2 cooled in a supersonic jet and excited to a single, B B-2(1) state rovibronic level at 22 994.92 cm(-1) above the ground-state zero point was detected with 10(-8)-s time resolution. The IR emission together with the laser-induced fluorescence decay measurement allows the deduction of the relaxation dynamics near the dissociation of NO2. Following the excitation this single rovibronic B B-2(1) level decays on 1.0-s time scale primarily through electronic radiation. Collisions induce internal conversion with a rate constant of 3.0x10(7) Torr(-1) s(-1) to the mixed A/X states. Collisions further induce internal conversion of the A/X mixed states into highly vibrationally excited levels in the X states with a rate constant at least one order of magnitude slower. This mechanism results in the observation of a double-exponential decay in the laser-induced fluorescence and a rise in the IR emission intensity corresponding to the fast decay in the fluorescence intensity. The IR emission rate of the highly vibrationally excited X-state levels is estimated to be about one order of magnitude larger than the isoenergetic A/X mixed states and much larger than the B B-2(1) level, both with much less vibrational excitation. (c) 2005 American Institute of Physics.