PULSE Institute, SLAC National Accelerator Laboratory, 2575, Sand Hill Road, Menlo Park, California 94025, USA.
1] PULSE Institute, SLAC National Accelerator Laboratory, 2575, Sand Hill Road, Menlo Park, California 94025, USA [2] Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305, USA.
Nat Commun. 2014 Jun 23;5:4235. doi: 10.1038/ncomms5235.
Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation--X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the ππ* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the nπ* state.
分子可以高效且有选择性地将光能转化为其他自由度。然而，要揭示光激发分子中电子和原子核的超快运动，这对当前的光谱方法来说是一个挑战。在这里，我们通过与超快 X 射线脉冲的相互作用来探索分子的光激发动力学，从而在光激发分子中产生一个高度局域的核心空穴，该空穴通过俄歇发射而衰减。我们发现，作为光激发- X 射线探测延迟函数的俄歇光谱，从元素特异性的角度来看，包含了关于核和电子自由度的有价值信息。对于碱基胸腺嘧啶，氧俄歇光谱向高动能转移，这是由于在ππ光激发态中特定的 C-O 键拉伸。随后，俄歇光谱向低动能转移显示了初始光激发态的电子弛豫，弛豫时间为 200fs。从头算模拟增强了我们的解释，并表明电子向 nπ态的衰减。
