通过计算X射线光谱绘制环[18]碳的瞬态结构
Mapping Transient Structures of Cyclo[18]Carbon by Computational X-Ray Spectra
AI总结：
本文通过第一性原理计算研究环[18]碳基态及碳1s激发态的二维势能面，揭示XPS和XAS光谱对键长变化敏感，可用于确定键长并监测聚炔型与累积烯型之间的瞬态结构转变。
摘要：
环[18]碳（C$_{18}$）的结构——无论是具有键长交替（BLA）的聚炔型，还是无BLA的累积烯型——早在成功合成之前就长期吸引着研究者。近期研究表明其基态为聚炔型，并存在累积烯型瞬态，但其动力学过程仍不清楚，且缺乏实验验证。本研究对C$_{18}$的依赖于键长（$R_1$和$R_2$）的二维势能面（PESs）进行了第一性原理理论研究，重点关注基态以及碳1s电离态和激发态。我们考察了X射线光谱在确定键长和监测瞬态结构方面的潜力，发现X射线光电子能谱（XPS）和X射线吸收谱（XAS）对这些变化都很敏感。利用由14种不同泛函优化得到的基态极小结构库，我们观察到用$ω$B97XD泛函预测的内层电子结合能可在0.9 eV范围内变化（290.3--291.2 eV）。与预测极小值出现在交替键长处的基态势能面不同，C1s电离态势能面预测极小值出现在键长相等处。在XAS谱中，1$π^*$和2$π^*$峰沿$R_1 = R_2$线随键长增大表现出红移。此外，增大$R_2$（固定$R_1$）导致先红移后蓝移，在$R_1 = R_2$处达到最小值。主要峰表明1$π^*$和2$π^*$均来自两个通道：能量重合的C1s$\ ightarrowπ^*_{z}$（面外）和C1s$\ ightarrowπ^*_{xy}$（面内）跃迁。
英文摘要：
The structure of cyclo[18]carbon (C$_{18}$), whether in its polyynic form with bond length alternation (BLA) or its cumulenic form without BLA, has long fascinated researchers, even prior to its successful synthesis. Recent studies suggest a polyynic ground state and a cumulenic transient state; however, the dynamics remain unclear and lack experimental validation. This study presents a first-principles theoretical investigation of the bond lengths ($R_1$ and $R_2$) dependent two-dimensional potential energy surfaces (PESs) of C$_{18}$, concentrating on the ground state and carbon 1s ionized and excited states. We examine the potential of X-ray spectra for determining bond lengths and monitoring transient structures, finding that both X-ray photoelectron (XPS) and absorption (XAS) spectra are sensitive to these variations. Utilizing a library of ground-state minimum structures optimized with 14 different functionals, we observe that core binding energies predicted with the $ω$B97XD functional can vary by 0.9 eV (290.3--291.2 eV). Unlike the ground state PES, which predicts minima at alternating bond lengths, the C1s ionized state PES predicts minima with equivalent bond lengths. In the XAS spectra, peaks 1$π^*$ and 2$π^*$ show a redshift with increasing bond lengths along the line where $R_1 = R_2$. Additionally, increasing $R_2$ (with $R_1$ fixed) results in an initial redshift followed by a blueshift, minimizing at $R_1 = R_2$. Major peaks indicate that both 1$π^*$ and 2$π^*$ arise from two channels: C1s$\rightarrowπ^*_{z}$ (out-of-plane) and C1s$\rightarrowπ^*_{xy}$ (in-plane) transitions at coinciding energies.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
