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–CH₃ bond predissociation of thioanisole (C₆H₅SCH₃) in the first electronically excited state (S₁). 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.

中文翻译：

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圆锥形交叉口非绝热分叉动力学的实时观察

精确定位在特征鲜明的圆锥形交叉点处的无功通量的时间动态一直是化学家的长期目标之一。我们在这里报告了在第一个电子激发态（S ₁）中硫代苯甲醚（C ₆ H ₅ SCH ₃）的S-CH ₃键预解离的实时非绝热分叉动力学）。发现只有在光学上接近第一个圆锥形交叉点附近的振动状态时，才同时激活两个不同的绝热和非绝热反应路径。我们对产物状态分布的时间分辨测量可以明确地分离出两个不同的动态通道，从而揭示了在圆锥形交叉点附近发生的非绝热反应的详细动力学机制。发现非绝热通道的反应通量沿着反应坐标通过两个连续的圆锥形交汇处漏斗，其速度显着快于沿着最小能量反应路径的绝热通道。发现非绝热通道的动能释放率和非绝热转变概率比绝热通道的动能释放率和非绝热转变概率高得多，