Department of Chemistry, KAIST , Daejeon 34141, Republic of Korea.
J Am Chem Soc. 2017 Nov 29;139(47):17152-17158. doi: 10.1021/jacs.7b09677. Epub 2017 Nov 17.
Looking into temporal dynamics of the reactive flux that is precisely located at the well-characterized conical intersection has been one of chemists' longstanding goals. We report here real-time nonadiabatic bifurcation dynamics in the S-CH bond predissociation of thioanisole (CHSCH) in the first electronically excited state (S). It is found that two distinct adiabatic and nonadiabatic reaction pathways are activated simultaneously only when the vibronic state near the first conical intersection is optically accessed. Our time-resolved measurement of the product state distribution could separate two different dynamic channels unambiguously, unraveling the detailed dynamic mechanism of the nonadiabatic reaction taking place in the vicinity of the conical intersection. The nonadiabatic channel, where the reactive flux funnels through two consecutive conical intersections along the reaction coordinate, is found to be significantly faster than the adiabatic channel along the minimum energy reaction pathway. The kinetic energy release ratio and the nonadiabatic transition probability are found to be much higher for the nonadiabatic channel than those of the adiabatic channel, giving insights into the bifurcation dynamics occurring at the conical intersection.
探究精确位于特征锥形交叉点处的反应通量的时间动力学一直是化学家的长期目标之一。我们在这里报告噻吩甲醚 (CHSCH) 在第一电子激发态 (S) 中 S-CH 键离解的实时非绝热分岔动力学。结果发现，只有当靠近第一个锥形交叉点的振子态被光学激发时，两个不同的绝热和非绝热反应途径才会同时被激活。我们对产物态分布的时间分辨测量可以明确地区分两个不同的动力学通道，揭示了在锥形交叉点附近发生的非绝热反应的详细动力学机制。发现非绝热通道中，反应通量沿着反应坐标通过两个连续的锥形交叉点，其速度明显快于沿着最小能量反应途径的绝热通道。非绝热通道的动能释放比和非绝热跃迁概率都比绝热通道高得多，这为在锥形交叉点处发生的分岔动力学提供了深入了解。
