Chicharro David V, Poullain Sonia Marggi, Zanchet Alexandre, Bouallagui Aymen, García-Vela Alberto, Senent María L, Rubio-Lago Luis, Bañares Luis
Departamento de Química Física (Unidad Asociada I+D+i al CSIC) , Facultad de Ciencias Químicas , Universidad Complutense de Madrid , 28040 Madrid , Spain . Email:
Departamento de Química , Módulo 13 , Facultad de Ciencias , Universidad Autónoma de Madrid , 28049 Madrid , Spain.
Chem Sci. 2019 May 22;10(26):6494-6502. doi: 10.1039/c9sc02140j. eCollection 2019 Jul 14.
The photochemistry of the ethyl radical following excitation to the 3p Rydberg state is investigated in a joint experimental and theoretical study. Velocity map images for hydrogen atoms detected from photoexcited isotopologues CHCH, CHCD and CDCH at ∼201 nm, are discussed along with high-level electronic structure calculations of potential energy curves and non-adiabatic coupling matrix elements (NACME). A novel mechanism governed by a conical intersection allowing prompt site-specific hydrogen-atom elimination is presented and discussed. For this mechanism to occur, an initial ro-vibrational excitation is allocated to the radical permitting to access this reaction pathway and thus to control the ethyl photochemistry. While hydrogen-atom elimination from cold ethyl radicals occurs through internal conversion into lower electronic states followed by slow statistical dissociation, prompt site-specific C elimination into CHCH + H, occurring through a fast non-adiabatic crossing to a valence bound state followed by dissociation through a conical intersection, is accessed by means of an initial ro-vibrational energy content into the radical. The role of a particularly effective vibrational promoting mode in this prompt photochemical reaction pathway is discussed.
在一项联合实验与理论研究中，对激发至3p里德堡态的乙基自由基的光化学进行了研究。讨论了在约201纳米处从光激发的同位素异构体CHCH、CHCD和CDCH检测到的氢原子的速度映射图像，以及势能曲线和非绝热耦合矩阵元（NACME）的高水平电子结构计算。提出并讨论了一种由锥形交叉控制的新机制，该机制允许迅速进行位点特异性氢原子消除。为了使这种机制发生，初始的转动-振动激发被分配给自由基，从而允许进入该反应途径，进而控制乙基的光化学。虽然冷乙基自由基的氢原子消除是通过内转换为较低电子态，然后进行缓慢的统计解离，但通过快速非绝热交叉到价束缚态，然后通过锥形交叉进行解离，迅速进行位点特异性C消除生成CHCH + H，这是通过自由基中初始转动-振动能量含量来实现的。讨论了一种特别有效的振动促进模式在这种迅速光化学反应途径中的作用。
