EVIDENCE FOR THE REACTION OF HIGHLY VIBRATIONALLY EXCITED CLO RADICALS WITH NITROGEN

The stratospheric trace gas chlorine dioxide diluted in nitrogen at no rmal pressure is irradiated with laser light at a wavelength of 308 nm , which corresponds essentially to the (X(2)B(1)0,0,0) --> (A(2)A(2)18 ,0,0) symmetric stretch progression of OClO. This highly vibrationally excited initial OClO state produces ClO(X-2 Pi(Omega),upsilon,J) radi cals containing almost the entire amount of excess energy in their int ernal degrees of freedom. The ClO fragments resulting from this dissoc iation process carry sufficient internal energy to exceed the activati on energy for the reaction with nitrogen. Accordingly, the reaction Cl O(upsilon >> 0) + N-2 --> Cl + N2O could represent an additional sourc e for nitrous oxide and atomic chlorine in the stratosphere. The gener ation of N2O is experimentally observed in a single-shot laser experim ent where the N2O is detected by means of a gas chromatograph. The exp erimental results indicate that there is in fact a strong evidence for the production of nitrous oxide via the vibrationally mediated reacti on of ClO radicals with abundant nitrogen molecules. (C) 1997 Elsevier Science B.V.