Woo Kyung Chul, Kim Junggil, Kim Sang Kyu
Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea.
J Phys Chem Lett. 2021 Feb 25;12(7):1854-1861. doi: 10.1021/acs.jpclett.0c03742. Epub 2021 Feb 12.
The dynamic role of the conical intersection "seam" coordinate has been first revealed in the H fragmentation reaction of -cresol conformers. One of the (3 - 8) dimensional seam coordinates of the S(ππ*)/S(πσ*) conical intersection has been identified as the CH torsional potential function. The tunneling dynamics of the reactive flux is dictated by its nuclear layout with respect to the CH torsional angle, as the multidimensional tunneling barrier is dynamically shaped along the conical intersection seam. The effective tunneling-barrier weight-averaged over the quantum-mechanical probability along the CH torsional angle perfectly explains the experimental finding: the sharp variation of the tunneling rate ((700-400) ps) with the CH torsional mode excitations within the narrow (0-100 cm) energetic window. The much longer S lifetime of compared to is ascribed to the higher-lying S/S conical intersection of the former. With the use of distinct lifetimes, vibronic bands of each conformer could be completely separated.
锥形交叉“缝”坐标的动态作用首先在对甲酚构象异构体的H碎片化反应中得以揭示。S(ππ*)/S(πσ*)锥形交叉的(3 - 8)维缝坐标之一已被确定为CH扭转势函数。反应通量的隧穿动力学由其相对于CH扭转角的核布局决定，因为多维隧穿势垒是沿着锥形交叉缝动态形成的。沿CH扭转角在量子力学概率上进行加权平均得到的有效隧穿势垒，完美地解释了实验结果：在狭窄的(0 - 100 cm)能量窗口内，隧穿速率((700 - 400) ps)随CH扭转模式激发的急剧变化。与相比，的S寿命长得多，这归因于前者具有更高能级的S/S锥形交叉。利用不同的寿命，可以完全分离每个构象异构体的振转带。
