核心级光谱解码环[18]碳的键长交替动力学

中文摘要 AI 辅助

X射线自由电子激光和高次谐波产生的出现，使时间分辨X射线光谱成为探测局域原子环境的强大工具，然而局域核心激发能否反映全局集体畸变仍是一个悬而未决的问题。环[18]碳（C$_{18}$）具有多炔基态（D$_\text{9h}$）和累积烯过渡态（D$_\text{18h}$），为解决键长交替（BLA）动力学中的这一长期问题提供了理想模型。通过第一性原理模拟绘制二维势能面，我们发现核心电离使基态双阱势沿BLA坐标对称化。我们计算的X射线光谱显示出对键长变化的显著敏感性：C1s电离势在BLA坐标（1.1--1.4~Å）范围内变化高达2.4~eV，不同泛函预测的极小值之间变化为0.9~eV，而NEXAFS $\pi^*$峰在同一坐标范围内移动高达4~eV。这些预测特征为未来超快X射线实验中解码瞬态结构以及实时监测键长交替动力学提供了定量的光谱-结构字典。

英文摘要

The advent of X-ray free-electron lasers and high-harmonic generation has made time-resolved X-ray spectroscopy a powerful tool for probing local atomic environments, yet whether localized core excitations can report on global collective distortions remains open. Cyclo[18]carbon (C$_{18}$), with its polyynic ground state (D$_\text{9h}$) and cumulenic transition state (D$_\text{18h}$), provides an ideal model to address this long-standing issue in bond-length alternation (BLA) dynamics. Mapping two-dimensional potential energy surfaces by first-principles simulations, we find that core ionization symmetrizes the ground-state double-well potential along the BLA coordinate. Our calculated X-ray spectra reveal remarkable sensitivity to bond-length variations: C1s ionization potentials vary by up to 2.4~eV across the BLA coordinate (1.1--1.4~Å), with a 0.9~eV variation for minima predicted by different functionals, while NEXAFS $π^*$ peaks shift by up to 4~eV across the same coordinate. These predicted signatures provide a quantitative spectroscopy--structure dictionary for decoding transient structures in future ultrafast X-ray experiments and monitoring bond-alternation dynamics in real time.

发表机构

• MIIT Key Laboratory of Semiconductor Microstructure and Quantum Sensing, School of Physics, Nanjing University of Science and Technology（南京理工大学物理学院）
• School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology（江苏科技大学环境化学工程学院）

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