Signatures of the Bromine Atom and Open-Shell Spin Coupling in the X-ray Spectrum of the Bromobenzene Cation
Signatures of the Bromine Atom and Open-Shell Spin Coupling in the X-ray Spectrum of the Bromobenzene Cation
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溴苯阳离子 X 射线谱中溴原子和开壳层自旋耦合的特征
DOI：
10.1021/jacs.2c12334
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发表时间：
2023
影响因子：
15
通讯作者：
Leone, Stephen R.
中科院分区：
文献类型：
--
作者：
Epshtein, Michael;Tenorio, Bruno Nunes;Vidal, Marta L.;Scutelnic, Valeriu;Yang, Zheyue;Xue, Tian;Krylov, Anna I.;Coriani, Sonia;Leone, Stephen R.
桌面x射线光谱测量在碳边辅以初始计算，研究了溴原子对溴苯阳离子（BrBz+）中碳核价跃迁的影响。用共振增强的双光子电离中性溴苯（BrBz）制备阳离子的电子基态，并用高谐波发生（HHG）产生的x射线探测。用一个溴原子取代苯中的一个氢原子，使碳原子（C*）与溴键的1sC*轨道的跃迁比其他碳原子(C)在x射线光谱中的能量更高（约1 eV）。在BrBz+中，x射线谱由两个相对强烈的跃迁主导，1sC→π*和1sC*→σ*(C* -Br)，其中第二次跃迁相对于中性BrBz增强。此外，在实验中观察到这两个跃迁的双峰形状。1sC→π*双重峰形状是由部分空π轨道（电离）上的未配对电子与从1sC轨道跃迁到完全空π*轨道上的另外两个未配对电子的自旋耦合引起的。1sC*→σ*双重峰形状是由UV电离后σ*和振动C* -Br模式激活的几个跃迁引起的，这表明C* -Br键长度对BrBz+的核价跃迁和弛豫几何形状有影响。
Tabletop X-ray spectroscopy measurements at the carbonK-edge complemented byab initiocalculations are used to investigate the influence of the bromine atom on the carbon core–valence transitions in the bromobenzene cation (BrBz+). The electronic ground state of the cation is prepared by resonance-enhanced two-photon ionization of neutral bromobenzene (BrBz) and probed by X-rays produced by high-harmonic generation (HHG). Replacing one of the hydrogen atoms in benzene with a bromine atom shifts the transition from the 1sC*orbital of the carbon atom (C*) bonded to bromine by ∼1 eV to higher energy in the X-ray spectrum compared to the other carbon atoms (C). Moreover, in BrBz+, the X-ray spectrum is dominated by two relatively intense transitions, 1sC→π* and 1sC*→σ*(C*–Br), where the second transition is enhanced relative to the neutral BrBz. In addition, a doublet peak shape for these two transitions is observed in the experiment. The 1sC→π* doublet peak shape arises due to the spin coupling of the unpaired electron in the partially vacant π orbital (from ionization) with the two other unpaired electrons resulting from the transition from the 1sCcore orbital to the fully vacant π* orbitals. The 1sC*→σ* doublet peak shape results from several transitions involving σ* and vibrational C*–Br mode activations following the UV ionization, which demonstrates the impact of the C*–Br bond length on the core–valence transition as well as on the relaxation geometry of BrBz+.