National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
Phys Chem Chem Phys. 2011 Apr 28;13(16):7312-21. doi: 10.1039/c0cp01641a. Epub 2011 Mar 21.
We observed fifteen photofragments upon photolysis of propenal (acrolein, CH(2)CHCHO) at 193 nm using photofragment translational spectroscopy and selective vacuum-ultraviolet (VUV) photoionization. All the photoproducts arise from nine primary and two secondary dissociation pathways. We measured distributions of kinetic energy of products and determined branching ratios of dissociation channels. Dissociation to CH(2)CHCO + H and CH(2)CH + HCO are two major primary channels with equivalent branching ratios of 33%. The CH(2)CHCO fragment spontaneously decomposes to CH(2)CH + CO. A proportion of primary products CH(2)CH from the fission of bond C-C of propenal further decompose to CHCH + H but secondary dissociation HCO → H + CO is negligibly small. Binary dissociation to CH(2)CH(2) (or CH(3)CH) + CO and concerted three-body dissociation to C(2)H(2) + CO + H(2) have equivalent branching ratios of 14%-15%. The other channels have individual branching ratios of ∼1%. The production of HCCO + CH(3) indicates the formation of intermediate methyl ketene (CH(3)CHCO) and the production of CH(2)CCH + OH and CH(2)CC + H(2)O indicate the formation of intermediate hydroxyl propadiene (CH(2)CCHOH) from isomerization of propenal. Distributions of kinetic energy release and dissociation mechanisms are discussed. This work provides a complete look and profound insight into the multi-channel dissociation mechanisms of propenal. The combination of a molecular beam apparatus and synchrotron VUV ionization allowed us to untangle the complex mechanisms of nine primary and two secondary dissociation channels.
我们在 193nm 波长下用光解丙烯醛（CH2CHCHO）的方法观察到了 15 个光碎片，并用光碎片平动光谱学和选择性真空紫外（VUV）光离子化技术进行了研究。所有的光产物都来自九条主要和两条次要的离解途径。我们测量了产物的动能分布，并确定了离解通道的分支比。到 CH2CHCO+H 和 CH2CH+HCO 的离解是两个主要的初级通道，分支比相等，均为 33%。CH2CHCO 碎片会自发分解为 CH2CH+CO。一部分丙烯醛的 C-C 键断裂产生的初级产物 CH2CH 会进一步分解为 CHCH+H，但次级离解 HCO→H+CO 可以忽略不计。二元离解为 CH2CH2（或 CH3CH）+CO 和协同三体离解为 C2H2+CO+H2 的分支比相等，均为 14%-15%。其他通道的分支比各约为 1%。HCCO+CH3 的生成表明中间甲基乙烯酮（CH3CHCO）的形成，而 CH2CCH+OH 和 CH2CC+H2O 的生成表明丙烯醛异构化生成中间羟基丙烯（CH2CCHOH）。我们讨论了动能释放分布和离解机制。这项工作全面深入地了解了丙烯醛的多通道离解机制。分子束装置和同步加速器 VUV 离子化的结合使我们能够理清九条主要和两条次要离解通道的复杂机制。
