Department of Chemistry and PULSE Institute, Stanford University, Stanford, California 94305, USA.
J Chem Phys. 2011 Jun 28;134(24):244306. doi: 10.1063/1.3604007.
Using a combined theoretical and experimental approach, we investigate the non-adiabatic dynamics of the prototypical ethylene (C(2)H(4)) molecule upon π → π∗ excitation. In this first part of a two part series, we focus on the lifetime of the excited electronic state. The femtosecond time-resolved photoelectron spectrum (TRPES) of ethylene is simulated based on our recent molecular dynamics simulation using the ab initio multiple spawning method with multi-state second order perturbation theory [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A 113, 13656 (2009)]. We find excellent agreement between the TRPES calculation and the photoion signal observed in a pump-probe experiment using femtosecond vacuum ultraviolet (hν = 7.7 eV) pulses for both pump and probe. These results explain the apparent discrepancy over the excited state lifetime between theory and experiment that has existed for ten years, with experiments [e.g., P. Farmanara, V. Stert, and W. Radloff, Chem. Phys. Lett. 288, 518 (1998) and K. Kosma, S. A. Trushin, W. Fuss, and W. E. Schmid, J. Phys. Chem. A 112, 7514 (2008)] reporting much shorter lifetimes than predicted by theory. Investigation of the TRPES indicates that the fast decay of the photoion yield originates from both energetic and electronic factors, with the energetic factor playing a larger role in shaping the signal.
采用理论和实验相结合的方法，我们研究了典型乙烯（C2H4）分子在π→π*激发下的非绝热动力学。在这一系列的两部分中的第一部分中，我们重点研究了激发电子态的寿命。基于我们最近使用从头算多生子方法和多态二级微扰理论进行的分子动力学模拟，模拟了乙烯的飞秒时间分辨光电子能谱（TRPES）[H. Tao, B. G. Levine 和 T. J. Martinez, J. Phys. Chem. A 113, 13656 (2009)]。我们发现 TRPES 计算与使用飞秒真空紫外（hν = 7.7 eV）脉冲进行泵浦-探测实验中观察到的光电子信号之间存在极好的一致性，其中泵浦和探测都使用了飞秒脉冲。这些结果解释了十年来理论和实验之间在激发态寿命上存在的明显差异，实验[例如，P. Farmanara, V. Stert 和 W. Radloff, Chem. Phys. Lett. 288, 518 (1998) 和 K. Kosma, S. A. Trushin, W. Fuss 和 W. E. Schmid, J. Phys. Chem. A 112, 7514 (2008)]报道的寿命比理论预测的要短得多。对 TRPES 的研究表明，光电子产额的快速衰减源于能量和电子因素，其中能量因素在信号形成中起着更大的作用。
