King Sarah B, Yandell Margaret A, Stephansen Anne B, Neumark Daniel M
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 København Ø, Denmark.
J Chem Phys. 2014 Dec 14;141(22):224310. doi: 10.1063/1.4903197.
Electron attachment to uracil was investigated by applying time-resolved photoelectron imaging to iodide-uracil (I(-)U) complexes. In these studies, an ultraviolet pump pulse initiated charge transfer from the iodide to the uracil, and the resulting dynamics of the uracil temporary negative ion were probed. Five different excitation energies were used, 4.00 eV, 4.07 eV, 4.14 eV, 4.21 eV, and 4.66 eV. At the four lowest excitation energies, which lie near the vertical detachment energy of the I(-)U complex (4.11 eV), signatures of both the dipole bound (DB) as well as the valence bound (VB) anion of uracil were observed. In contrast, only the VB anion was observed at 4.66 eV, in agreement with previous experiments in this higher energy range. The early-time dynamics of both states were highly excitation energy dependent. The rise time of the DB anion signal was ∼250 fs at 4.00 eV and 4.07 eV, ∼120 fs at 4.14 eV and cross-correlation limited at 4.21 eV. The VB anion rise time also changed with excitation energy, ranging from 200 to 300 fs for excitation energies 4.00-4.21 eV, to a cross-correlation limited time at 4.66 eV. The results suggest that the DB state acts as a "doorway" state to the VB anion at 4.00-4.21 eV, while direct attachment to the VB anion occurs at 4.66 eV.
通过对碘化物 - 尿嘧啶（I(-)U）络合物应用时间分辨光电子成像技术，研究了电子与尿嘧啶的附着情况。在这些研究中，一个紫外泵浦脉冲引发了从碘化物到尿嘧啶的电荷转移，并探测了尿嘧啶临时负离子的后续动力学。使用了五种不同的激发能量，分别为4.00电子伏特、4.07电子伏特、4.14电子伏特、4.21电子伏特和4.66电子伏特。在四个最低激发能量下，即接近I(-)U络合物的垂直脱附能量（4.11电子伏特）时，观察到了尿嘧啶的偶极束缚（DB）以及价态束缚（VB）阴离子的特征。相比之下，在4.66电子伏特时仅观察到了VB阴离子，这与该较高能量范围内的先前实验结果一致。两种状态的早期动力学都高度依赖于激发能量。DB阴离子信号的上升时间在4.00电子伏特和4.07电子伏特时约为250飞秒，在4.14电子伏特时约为120飞秒，在4.21电子伏特时受互相关限制。VB阴离子的上升时间也随激发能量而变化，对于4.00 - 4.21电子伏特的激发能量，上升时间在200到300飞秒之间，在4.66电子伏特时为互相关限制时间。结果表明，在4.00 - 4.21电子伏特时，DB态充当了通向VB阴离子的“门道”态，而在4.66电子伏特时则直接附着到VB阴离子上。
