| Summary: | These studies investigate the photodissociation of 2-bromoethylnitrite, BrCH2CH2ONO, at 351 nm and 193 nm, using a crossed laser-molecular beam scattering apparatus with electron bombardment detection and a velocity map imaging apparatus with tunable VUV photoionization detection. At 351 nm, the only photodissociation channel of the precursor we detected was O-NO bond fission. At 351 nm, some but not all of the BrCH2CH2O radicals are formed with enough internal energy to unimolecularly dissociate to CH2Br + H2CO. 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. We also detected signal at m/e=42 using electron bombardment ionization. Comparison of that signal strength with the signal at HBr+, however, shows that the vinoxy product does not have HBr as a co-fragment, so the prior suggestion by Miller and co-workers (J. Phys. Chem. 2012, 116, 12032) that the vinoxy might result from a roaming mechanism is contraindicated.
Hoping to develop a photolytic precursor for the CH2CH 2ONO radical, I also investigated the photodissociation of BrCH 2CH2ONO at 193 nm. The experimental data determined the branching ratio between primary O-NO photofission and C-Br photofission to be 4.28:1(O-NO/C-Br). At 193 nm, all of the BrCH2CH2O radicals are formed with enough internal energy to unimolecularly dissociate to CH2Br + H2CO or to BrCH2CHO + H. We also investigated the possibility of the BrCH2CH2O → CH2CHO + HBr reaction arising from the vibrationally excited BrCH2CH 2O radicals produced from O-NO primary photodissociation. Signal strengths at HBr+, however, demonstrate that the vinoxy product does not have HBr as a co-fragment, so the BrCH2CH2O → HBr + vinoxy channel is negligible compared to the CH2Br + H 2CO channel. We also report our computational prediction of the unimolecular dissociation channels of the vibrational excited CH2CH2ONO radical resulting from C-Br bond photofission.
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