Ramphal Isaac A, Shapero Mark, Haibach-Morris Courtney, Neumark Daniel M
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Phys Chem Chem Phys. 2017 Nov 8;19(43):29305-29314. doi: 10.1039/c7cp05490d.
Photofragment translational spectroscopy was used to study the photodissociation of fulvenallene, CH, and the fulvenallenyl radical, CH, at 248 nm and 193 nm. Starting from fulvenallene, only the H-atom loss channel producing the fulvenallenyl radical, CH, was observed. Fulvenallene dissociation occurs on the ground state surface with no exit barrier, and there is good agreement between our experimentally determined photofragment translational energy distribution and a prior distribution for a statistical process. Subsequent absorption at both wavelengths by fulvenallenyl enabled investigation of the photodissociation of this radical. Two channels were observed: CH + CH and CH + CH. The photofragment translational energy distributions for these channels are peaked away from 0 kcal mol, which is consistent with ground state dissociation over an exit barrier. At 248 nm, the CH-loss channel accounted for 85 ± 10% of fulvenallenyl dissociation, while at 193 nm it accounted for 80 ± 15%. The experimental branching between these channels is in reasonable agreement with Rice-Ramsperger-Kassel-Marcus theory calculations, which predict CH-loss to account for 70% and 63% of dissociation for 248 nm and 193 nm respectively.
光碎片平移光谱法被用于研究富烯丙二烯（CH）和富烯丙二烯基自由基（CH）在248纳米和193纳米处的光解离。从富烯丙二烯开始，仅观察到产生富烯丙二烯基自由基（CH）的氢原子损失通道。富烯丙二烯的解离发生在基态表面，没有出射势垒，并且我们实验测定的光碎片平移能量分布与统计过程的先验分布之间有很好的一致性。富烯丙二烯基随后在这两个波长处的吸收使得能够研究该自由基的光解离。观察到两个通道：CH + CH和CH + CH。这些通道的光碎片平移能量分布在远离0千卡/摩尔处达到峰值，这与通过出射势垒的基态解离一致。在248纳米处，CH损失通道占富烯丙二烯基解离的85±10%，而在193纳米处占80±15%。这些通道之间的实验分支比与赖斯-拉姆齐-卡斯尔-马库斯理论计算结果合理相符，该理论计算预测在248纳米和193纳米处CH损失分别占解离的70%和63%。
