VIBRONIC INTERACTIONS IN NO3 - FROM THE (2)E' ORIGIN REGION TO THE NO-2 REACTIVE CHANNEL(O)

LIF spectra of expansion-cooled NO3 in the region 595-666 nm reveal vi bronic interactions responsible for (2)E' radiationless decay, A hiera rchy of coupling strengths is suggested. Due the large atomic masses, tunneling results in small unimolecular decomposition rates below the NO + O-2 barrier on the (2)A'(2) ground potential surface. These have been observed via their quenching of long-lived NO3 fluorescence, and rates as small as 3 x 10(4) s(-1) are reported. This is 5 orders of ma gnitude smaller than the rate just above the barrier, which had been d etermined previously by using the ultrafast pump-probe technique.