1 Departments of Chemistry , and Physics and Astronomy , University of California , Irvine , CA 92697 , USA.
2 Department of Chemistry , Sungkyunkwan University , Suwon 16419 , Korea.
Philos Trans A Math Phys Eng Sci. 2019 May 20;377(2145):20170470. doi: 10.1098/rsta.2017.0470.
X-ray diffraction signals from the time-evolving molecular charge density induced by selective core excitation of chemically inequivalent carbon atoms are calculated. A narrowband X-ray pulse selectively excites the carbon K-edge of the -CH or -CHF groups in fluoroethane (CH-CHF). Each excitation creates a distinct core coherence which depends on the character of the electronic transition. Direct propagation of the reduced single-electron density matrix, using real-time time-dependent density functional theory, provides the time-evolving charge density following interactions with external fields. The interplay between partially filled valence molecular orbitals upon core excitation induces characteristic femtosecond charge migration which depends on the core-valence coherence, and is monitored by the sum-frequency generation diffraction signal. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.
计算了由化学不等价碳原子的选择性芯激发诱导的时变分子电荷密度的 X 射线衍射信号。窄带 X 射线脉冲选择性地激发氟乙烷（CH-CHF）中-CH 或-CHF 基团的碳 K 边。每个激发都会产生一个依赖于电子跃迁性质的独特芯相干。使用实时时间相关密度泛函理论直接传播还原的单电子密度矩阵，提供了与外部场相互作用后随时间变化的电荷密度。芯激发后部分填充的价分子轨道之间的相互作用诱导了特征飞秒电荷迁移，这取决于芯-价相干，并且可以通过和频产生衍射信号来监测。本文是“用 X 射线测量超快电子和结构动力学”主题特刊的一部分。
