University of California at Berkeley, Berkeley, California 94720, USA.
J Chem Phys. 2012 Mar 28;136(12):124317. doi: 10.1063/1.3697760.
Through a combined experimental and theoretical approach, we study the nonadiabatic dynamics of the prototypical ethylene (C(2)H(4)) molecule upon π → π(∗) excitation with 161 nm light. Using a novel experimental apparatus, we combine femtosecond pulses of vacuum ultraviolet and extreme ultraviolet (XUV) radiation with variable delay to perform time resolved photo-ion fragment spectroscopy. In this second part of a two part series, the XUV (17 eV < hν < 23 eV) probe pulses are sufficiently energetic to break the C-C bond in photoionization, or to photoionize the dissociation products of the vibrationally hot ground state. The experimental data is directly compared to excited state ab initio molecular dynamics simulations explicitly accounting for the probe step. Enhancements of the CH(2)(+) and CH(3)(+) photo-ion fragment yields, corresponding to molecules photoionized in ethylene (CH(2)CH(2)) and ethylidene (CH(3)CH) like geometries are observed within 100 fs after π → π(∗) excitation. Quantitative agreement between theory and experiment on the relative CH(2)(+) and CH(3)(+) yields provides experimental confirmation of the theoretical prediction of two distinct conical intersections and their branching ratio [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A. 113, 13656 (2009)]. Evidence for fast, non-statistical, elimination of H(2) molecules and H atoms is observed in the time resolved H(2)(+) and H(+) signals.
通过实验和理论相结合的方法，我们研究了在 161nm 光激发下典型乙烯（C2H4）分子的非绝热动力学。利用一种新型的实验装置，我们将真空紫外和极紫外（XUV）辐射的飞秒脉冲与可变延迟相结合，进行时间分辨光致碎片光谱研究。在这个两部分系列的第二部分中，XUV（17eV<hν<23eV）探测脉冲具有足够的能量来断裂光致电离过程中的 C-C 键，或者光致电离振动激发的基态的离解产物。实验数据与明确考虑到探测步骤的激发态从头算分子动力学模拟进行了直接比较。在π→π*激发后 100fs 内，观察到 CH2+和 CH3+光致碎片产额增强，对应于乙烯（CH2CH2）和亚乙基（CH3CH）类似几何形状的分子光致电离。理论与实验在相对 CH2+和 CH3+产额上的定量一致性提供了对两个不同的锥形交叉点及其分支比的理论预测的实验证实[H. Tao、B.G. Levine 和 T.J. Martinez，J. Phys. Chem. A 113，13656（2009）]。在时间分辨的 H2+和 H+信号中观察到 H2分子和 H 原子快速、非统计消除的证据。
