School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
J Chem Phys. 2011 Sep 28;135(12):124305. doi: 10.1063/1.3638689.
Picosecond time-resolved photoelectron spectroscopy is used to investigate intramolecular vibrational redistribution (IVR) following excitation of S(1) 18a(1) in p-fluorotoluene (pFT) at an internal energy of 845 cm(-1), where ν(18a) is a ring bending vibrational mode. Characteristic oscillations with periods of 8 ps and 5 ps are observed in the photoelectron signal and attributed to coupling between the initially excited zero-order bright state and two doorway states. Values for the coupling coefficients connecting these three vibrational states have been determined. In addition, an exponential change in photoelectron signal with a lifetime of 17 ps is attributed to weaker couplings with a bath of dark states that play a more significant role during the latter stages of IVR. A tier model has been used to assign the most strongly coupled doorway state to S(1) 17a(1) 6a(2)('), where ν(17a) is a CH out-of-plane vibrational mode and 6a(2)(') is a methyl torsional level. This assignment signifies that a torsion-vibration coupling mechanism mediates the observed dynamics, thus demonstrating the important role played by the methyl torsional mode in accelerating IVR.
皮秒时间分辨光电子能谱用于研究在内部能量为 845 cm(-1)时，p-氟甲苯（pFT）中 S(1) 18a(1)激发后分子内振动再分配（IVR）。ν(18a)是一个环弯曲振动模式。在光电子信号中观察到具有 8 ps 和 5 ps 周期的特征振荡，归因于初始激发的零阶亮态与两个门道态之间的耦合。已经确定了连接这三个振动态的耦合系数的值。此外，光电子信号随寿命为 17 ps 的指数变化归因于与暗态浴的较弱耦合，暗态在 IVR 的后期阶段起着更重要的作用。使用层模型将最强烈耦合的门道态分配给 S(1) 17a(1) 6a(2)(')，其中 ν(17a)是 CH 面外振动模式，6a(2)(')是甲基扭转能级。该分配表示扭转-振动耦合机制介导了观察到的动力学，从而证明了甲基扭转模式在加速 IVR 中所起的重要作用。
