Couch David E, Kapteyn Henry C, Murnane Margaret M, Peters William K
JILA and Department of Physics, University of Colorado , Boulder, Colorado 80309, United States.
J Phys Chem A. 2017 Mar 30;121(12):2361-2366. doi: 10.1021/acs.jpca.7b01112. Epub 2017 Mar 17.
Understanding the ultrafast dynamics of highly excited electronic states of small molecules is critical for a better understanding of atmospheric and astrophysical processes, as well as for designing coherent control strategies for manipulating chemical dynamics. In highly excited states, nonadiabatic coupling, electron-electron interactions, and the high density of states govern dynamics. However, these states are computationally and experimentally challenging to access. Fortunately, new sources of ultrafast vacuum ultraviolet pulses, in combination with electron-ion coincidence spectroscopies, provide new tools to unravel the complex electronic landscape. Here we report time-resolved photoelectron-photoion coincidence experiments using 8 eV pump photons to study the highly excited states of acetone. We uncover for the first time direct evidence that the resulting excited state consists of a mixture of both n → 3p and π → π* character, which decays with a time constant of 330 fs. In the future, this approach can inform models of VUV photochemistry and aid in designing coherent control strategies for manipulating chemical reactions.
理解小分子高激发电子态的超快动力学，对于更好地理解大气和天体物理过程，以及设计用于操纵化学动力学的相干控制策略至关重要。在高激发态下，非绝热耦合、电子 - 电子相互作用和高态密度主导着动力学。然而，这些状态在计算和实验上都难以获取。幸运的是，超快真空紫外脉冲的新光源与电子 - 离子符合光谱学相结合，提供了揭示复杂电子态势的新工具。在此，我们报告了使用8 eV泵浦光子进行的时间分辨光电子 - 光离子符合实验，以研究丙酮的高激发态。我们首次发现直接证据，表明所产生的激发态由n → 3p和π → π*特征的混合物组成，其以330 fs的时间常数衰减。未来，这种方法可为真空紫外光化学模型提供信息，并有助于设计用于操纵化学反应的相干控制策略。
