Photoproduct Channels from BrCD2CD2OH at 193 nm and the HDO + Vinyl Products from the CD2CD2OH Radical Intermediate

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• 作者：Caroline C. Womack ; Britni J. Ratliff ; Laurie J. Butler ; Shih-Huang Lee ; Jim Jr-Min Lin
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：June 21, 2012
• 年：2012
• 卷：116
• 期：24
• 页码：6394-6407
• 全文大小：615K
• 年卷期：v.116,no.24(June 21, 2012)
• ISSN：1520-5215

文摘

We present the results of our product branching studies of the OH + C₂D₄ reaction, beginning at the CD₂CD₂OH radical intermediate of the reaction, which is generated by the photodissociation of the precursor molecule BrCD₂CD₂OH at 193 nm. Using a crossed laser-molecular beam scattering apparatus with tunable photoionization detection, and a velocity map imaging apparatus with VUV photoionization, we detect the products of the major primary photodissociation channel (Br and CD₂CD₂OH), and of the secondary dissociation of vibrationally excited CD₂CD₂OH radicals (OH, C₂D₄/CD₂O, C₂D₃, CD₂H, and CD₂CDOH). We also characterize two additional photodissociation channels, which generate HBr + CD₂CD₂O and DBr + CD₂CDOH, and measure the branching ratio between the C鈥揃r bond fission, HBr elimination, and DBr elimination primary photodissociation channels as 0.99:0.0064:0.0046. The velocity distribution of the signal at m/e = 30 upon 10.5 eV photoionization allows us to identify the signal from the vinyl (C₂D₃) product, assigned to a frustrated dissociation toward OH + ethene followed by D-atom abstraction. The relative amount of vinyl and Br atom signal shows the quantum yield of this HDO + C₂D₃ product channel is reduced by a factor of 0.77 卤 0.33 from that measured for the undeuterated system. However, because the vibrational energy distribution of the deuterated radicals is lower than that of the undeuterated radicals, the observed reduction in the water + vinyl product quantum yield likely reflects the smaller fraction of radicals that dissociate in the deuterated system, not the effect of quantum tunneling. We compare these results to predictions from statistical transition state theory and prior classical trajectory calculations on the OH + ethene potential energy surface that evidenced a roaming channel to produce water + vinyl products and consider how the branching to the water + vinyl channel might be sensitive to the angular momentum of the 尾-hydroxyethyl radicals.