Phenol can serve as a model for examining the deactivation of the aromatic amino acid tyrosine following UV excitation, which mainly occurs through a repulsive πσ^* state along the O–H bond. The reaction barrier formed by the conical intersection between the optically bright S₁ (ππ^*) state and the dissociative S₂ (πσ^*) state does not inhibit O–H bond rupture even though the excitation energy is below the barrier height. To examine the O–H bond-rupture dynamics in association with the initial excited vibrational modes, we used a picosecond laser to investigate the vibrational-mode-dependent excited-state lifetime of phenol under the S₁/S₂ conical intersection. Unexpectedly short lifetimes were observed in the S₁ state for a″ symmetric vibrational modes (including v₄, v_16a, τOH, and v₅). These results clarify recent theoretical calculations showing that the relaxation from S₁ to S₂ either occurs via symmetry-allowed non-adiabatic transitions or is topographically linked to a lower energy minimum on the multidimensional potential energy surface.

中文翻译：

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通讯：S1 / S2圆锥形交点下苯酚的依赖于模式的激发态寿命

苯酚可以用作检查紫外线激发后芳香族氨基酸酪氨酸失活的模型，该失活主要是通过沿O–H键的排斥性πσ ^*状态发生的。即使在激发能低于势垒高度的情况下，由光学亮的S ₁（ππ ^*）状态和解离的S ₂（πσ ^*）状态之间的圆锥形交点形成的反应势垒也不会抑制O–H键断裂。为了检查与初始激发振动模式相关的O–H键断裂动力学，我们使用了皮秒激光研究了在S ₁ / S ₂下苯酚的振动模式相关的激发态寿命。圆锥形相交。对于对称振动模式（包括v ₄，v _16a，τOH和v ₅），在S ₁状态下观察到了意想不到的短寿命。这些结果澄清了最近的理论计算，表明从S ₁到S ₂的弛豫要么通过对称允许的非绝热跃迁发生，要么在地形上与多维势能表面上的最低能量最小值相关。