Imaging and Scattering Studies of the Unimolecular Dissociation of the BrCH sub(2)CH sub(2)O Radical from BrCH sub(2)CH sub(2)ONO Photolysis at 351 nm

We report a study of the unimolecular dissociation of BrCH sub(2)CH sub(2)O radicals produced from the photodissociation of BrCH sub(2)CH sub(2)ONO at 351/355 nm. Using both a crossed laser-molecular beam scattering apparatus with electron bombardment detection and a velocity map imaging apparatus with tunable VUV photoionization detection, we investigate the initial photodissociation channels of the BrCH sub(2)CH sub(2)ONO precursor and the subsequent dissociation of the vibrationally excited BrCH sub(2)CH sub(2)O radicals. The only photodissociation channel of the precursor we detected upon photodissociation at 351 nm was O-NO bond fission. C-Br photofission and HBr photoelimination do not compete significantly with O-NO photofission at this excitation wavelength. The measured O-NO photofission recoil kinetic energy distribution peaks near 14 kcal/mol and extends from 5 to 24 kcal/mol. There is also a small signal from lower kinetic energy NO product (it would be 6% of the total if it were also from O-NO photofission). We use the O-NO photofission P(E sub(T)) peaking near 14 kcal/mol to help characterize the internal energy distribution in the nascent ground electronic state BrCH sub(2)CH sub(2)O radicals. At 351 nm, some but not all of the BrCH sub(2)CH sub(2)O radicals are formed with enough internal energy to unimolecularly dissociate to CH sub(2)Br + H sub(2)CO. Although the signal at m/e = 93 (CH sub(2)Br super(+)) obtained with electron bombardment detection includes signal both from the CH sub(2)Br product and from dissociative ionization of the energetically stable BrCH sub(2)CH sub(2)O radicals, we were able to isolate the signal from CH sub(2)Br product alone using tunable VUV photoionization detection at 8.78 eV. We also sought to investigate the source of vinoxy radicals detected in spectroscopic experiments by Miller and co-workers ( J. Phys. Chem. A 2012, 116, 12032) from the photodissociation of BrCH sub(2)CH sub(2)ONO at 351 nm. Using velocity map imaging and photodissociating the precursor at 355 nm, we detected a tiny signal at m/e = 43 and a larger signal at m/e = 15 that we tentatively assign to vinoxy. An underlying signal in the time-of-flight spectra at m/e = 29 and m/e = 42, the two strongest peaks in the literature electron bombardment mass spectrum of vinoxy, is also apparent. Comparison of those signal strengths with the signal at HBr super(+), however, shows that the vinoxy product does not have HBr as a cofragment, so the pri