We used crossed laser-molecular beam scattering to study the primary photodissociation channels of chloroacetaldehyde (CH₂ClCHO) at 157 nm. In addition to the C–Cl bond fission primary photodissociation channel, the data evidence two other photodissociation channels: HCl photoelimination and C–C bond fission. This is the first direct evidence of the C–C bond fission channel in chloroacetaldehyde, and we found that it significantly competes with the C–Cl bond fission channel. We determined the total primary photodissociation branching fractions for C–Cl fission:HCl elimination:C–C fission to be 0.65:0.07:0.28. The branching between the primary channels suggests the presence of interesting excited state dynamics in chloroacetaldehyde. Some of the vinoxy radicals from C–Cl photofission and most of the ketene cofragments formed in HCl photoelimination have enough internal energy to undergo secondary dissociation. While our previous velocity map imaging study on the photodissociation of chloroacetaldehyde at 157 nm focused on the barrier for the unimolecular dissociation of vinoxy to H + ketene, this work shows that the HCl elimination channel contributed to the high kinetic energy portion of the m/z = 42 signal in that study.

中文翻译：

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初级产物在157 nm处的氯乙醛光解离中分支

我们使用交叉激光分子束散射研究了氯乙醛（CH ₂ClCHO）在157 nm。除了C–Cl键裂变的主要光解离通道外，数据还证明了另外两个光解离通道：HCl光消除和C–C键裂变。这是氯乙醛中C–C键裂变通道的第一个直接证据，我们发现它与C–Cl键裂变通道显着竞争。我们确定C–Cl裂变：HCl消除：CC裂变的总初级光解离支化分数为0.65：0.07：0.28。主通道之间的分支表明，在氯乙醛中存在有趣的激发态动力学。C-Cl光裂变产生的一些乙烯基自由基和HCl光消除过程中形成的大多数乙烯酮共碎片具有足够的内部能量，可以进行二次解离。在该研究中，m / z = 42信号。