Abstract. Pulsed
laser excitation of NO2 (532–647 nm) or NO3
(623–662 nm) in the presence of H2O was used to initiate the
gas-phase reaction NO2∗+H2O → products
(Reaction R5) and NO3∗+H2O → products
(Reaction R12). No evidence for OH production in Reactions (R5) or
(R12) was observed
and upper limits for OH production of k5b/k5<1×10-5 and
k12b/k12<0.03 were assigned. The upper limit for k5b∕k5
renders this reaction insignificant as a source of OH in the atmosphere and
extends the studies (Crowley and Carl, 1997; Carr et al., 2009; Amedro et
al., 2011) which demonstrate that the previously reported large OH yield by
Li et al. (2008) was erroneous. The upper limit obtained for k12b∕k12 indicates that non-reactive energy transfer is the dominant mechanism
for Reaction (R12), though
generation of small but significant amounts of atmospheric
HOx and HONO cannot be ruled out. In the course of this
work, rate coefficients for overall removal of NO3∗ by
N2 (Reaction R10) and by H2O (Reaction R12) were
determined: k10=(2.1±0.1)×10-11 cm3 molecule−1 s−1 and k12=(1.6±0.3)×10-10 cm3 molecule−1 s−1. Our value of
k12 is more than a factor of 4 smaller than the single previously
reported value.
Reactive quenching of electronically excited NO<sub>2</sub><sup>∗</sup> and NO<sub>3</sub><sup>∗</sup> by H<sub>2</sub>O as potential sources of atmospheric HO<sub><i>x</i></sub> radicals
