Evidence for the reaction of highly vibrationally excited ClO radicals with nitrogen

Abstract

The stratospheric trace gas chlorine dioxide diluted in nitrogen at normal pressure is irradiated with laser light at a wavelength of 308 nm, which corresponds essentially to the (X 2B 10,0,0) → (A 2A 218,0,0) symmetric stretch progression of OClO. This highly vibrationally excited initial OClO state produces ClO(X 2Π Ω, v, J) radicals containing almost the entire amount of excess energy in their internal degrees of freedom. The ClO fragments resulting from this dissociation process carry sufficient internal energy to exceed the activation energy for the reaction with nitrogen. Accordingly, the reaction ClO( v≫0)+N 2 → Cl+N 2O could represent an additional source for nitrous oxide and atomic chlorine in the stratosphere. The generation of N 2O is experimentally observed in a single-shot laser experiment where the N 2O is detected by means of a gas chromatograph. The experimental results indicate that there is in fact a strong evidence for the production of nitrous oxide via the vibrationally mediated reaction of ClO radicals with abundant nitrogen molecules.