Rate coefficients for photoinitiated NO2 unimolecular decomposition: energy dependence in the threshold regime

Rate coefficients k(E) for photoinitiated NO2 unimolecular decomposition have been obtained by recording the product NO laser-induced fluorescence signal intensity versus the delay between the pump and probe pulses. A 10 ps pump-probe cross-correlation temporal width provides a useful compromise between time and frequency resolution (3 cm−1). k(E) increases rapidly: from ∼2×1010 to ⩾1.3×1011 s−1 within 25 cm−1 of reaction threshold. In this regime, long-range interfragment interactions play an important role. A high level of theory will be needed to reconcile these results.