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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Gas-Phase Retro-Diels-Alder Reactions of Cyclohexene, 1-Methylcyclohexene, and 4-Methylcyclohexene following Photoexcitation at 193 nm: A Velocity-Map Imaging Study
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Gas-Phase Retro-Diels-Alder Reactions of Cyclohexene, 1-Methylcyclohexene, and 4-Methylcyclohexene following Photoexcitation at 193 nm: A Velocity-Map Imaging Study

机译：环己烯，1-甲基环己烯和4-甲基环己烯在193 nm的光激发后气相逆Diels-Alder反应：速度图成像研究

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摘要

We present the results of a velocity-map imaging study into the retro-Diels-Alder (RDA) reactions of cyclohexene, 1-methylcyclohexene, and 4-methylcyclohexene following photoexcitation at 193 nm. Universal detection of all neutral fragments via vacuum-ultraviolet photoionization at 118 nm allows imaging of both RDA fragments in all cases. Fragment kinetic energy distributions reveal contributions from both dissociative ionization and retro-Diels-Alder reaction of the respective parent molecules, yielding reaction products with a high degree of internal excitation. Together with the observed isotropic product angular distributions, this is consistent with a mechanism in which the RDA reaction occurs from high vibrational levels of the electronic ground state following internal conversion from a higher-lying state initially populated in the photoexcitation process, as predicted by frontier molecular orbital theory. Velocity-map images and total translational energy distributions for the RDA products of 1-methylcyclohexene and 4-methylcyclohexene are very similar to those for unsubstituted cyclohexene, indicating that methyl substitution either adjacent to or far from the double bond has little effect on the dynamics of the RDA process.
机译：我们介绍了在193 nm光激发后环己烯，1-甲基环己烯和4-甲基环己烯的逆Diels-Alder（RDA）反应的速度图成像研究的结果。通过在118 nm的真空紫外光电离对所有中性片段进行通用检测，可以在所有情况下对两个RDA片段进行成像。碎片动能分布揭示了各自母体分子的离解电离和逆Diels-Alder反应两者的贡献，产生了具有高度内部激发的反应产物。与观察到的各向同性产物角分布一起，这与如下机制是一致的：RDA反应是由电子基态的高振动水平发生的，这是由光激发过程中最初填充的高位态进行内部转换后发生的，这是由前沿预测的分子轨道理论。 1-甲基环己烯和4-甲基环己烯的RDA产物的速度图图像和总平移能分布与未取代的环己烯的速率图图像和总平移能分布非常相似，这表明与双键相邻或相距较远的甲基取代对其动力学的影响很小。 RDA流程。

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