Vibronic interactions in NO3: from the 2E′ origin region to the NO + O2 reactive channel

LIF spectra of expansion-cooled NO3 in the region 595–666 nm reveal vibronic interactions responsible for 2E′ radiationless decay. A hierarchy of coupling strengths is suggested. Due the large atomic masses, tunneling results in small unimolecular decomposition rates below the NO + O2 barrier on the 2A′2 ground potential surface. These have been observed via their quenching of long-lived NO3 fluorescence, and rates as small as 3 × 104 s−1 are reported. This is 5 orders of magnitude smaller than the rate just above the barrier, which had been determined previously by using the ultrafast pump-probe technique.