Chen Wentao, Zhang Liang, Yuan Daofu, Chang Yao, Yu Shengrui, Wang Siwen, Wang Tao, Jiang Bin, Yuan Kaijun, Yang Xueming, Wang Xingan
Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
J Phys Chem Lett. 2019 Sep 5;10(17):4783-4787. doi: 10.1021/acs.jpclett.9b01811. Epub 2019 Aug 8.
The textbook mechanism for OCS photodissociation mainly involves the CO + S or CS + O product channel via a single bond fission. However, a third dissociation channel concerning the cleavage of both C-S and C-O bonds yielding SO + C products, though thermodynamically allowed, has never been verified experimentally to date. By using a tunable vacuum ultraviolet laser light and time-sliced velocity map ion imaging technique, we have clearly observed the SO(XΣ) + C(P) products as the vacuum ultraviolet laser photon energy gradually exceeds its thermodynamic threshold. The corresponding SO(XΣ) coproducts are highly vibrationally excited and show varying angular distributions from isotropic to anisotropic as the excitation photon energy increases. Theoretical analysis suggests that a fast nonadiabatic pathway plays a dominant role in the formation of the anisotropic SO products. That isotropic products arise as the excitation photon energies approach the thermodynamic threshold can be reasonably explained by the "roaming mechanism".
氧硫化碳（OCS）光解离的传统机制主要涉及通过单键断裂生成CO + S或CS + O产物通道。然而，尽管从热力学角度来看是允许的，但涉及C-S和C-O键同时断裂生成SO + C产物的第三种解离通道，迄今为止从未得到实验验证。通过使用可调谐真空紫外激光和时间切片速度映射离子成像技术，当真空紫外激光光子能量逐渐超过其热力学阈值时，我们清晰地观测到了SO(XΣ) + C(P)产物。相应的SO(XΣ)副产物具有高度的振动激发，并且随着激发光子能量的增加，呈现出从各向同性到各向异性的不同角分布。理论分析表明，一条快速非绝热途径在各向异性SO产物的形成中起主导作用。当激发光子能量接近热力学阈值时出现各向同性产物，这可以通过“漫游机制”得到合理的解释。
