Breaking inversion symmetry by protonation: experimental and theoretical NEXAFS study of the diazynium ion, N2H+
Breaking inversion symmetry by protonation: experimental and theoretical NEXAFS study of the diazynium ion, N2H+
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通过质子化打破反演对称性：二嗪鎓离子 N2H 的实验和理论 NEXAFS 研究
DOI：
10.1039/d1cp02002a
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发表时间：
2021
影响因子：
3.3
通讯作者：
Carravetta Vincenzo
中科院分区：
文献类型：
--
作者：
Couto Rafael C.;Hua Weijie;Lindblad Rebecka;Kjellsson Ludvig;Sorensen Stacey L.;Kubin Markus;Bulow Christine;Timm Martin;Zamudio-Bayer Vicente;von Issendorff Bernd;Soderstrom Johan;Lau J. Tobias;Rubensson Jan-Erik;Agren Hans;Carravetta Vincenzo
作为质子化物质 NEXAFS 光谱中对称性破缺的一个例子，我们展示了质子化二氮（二嗪鎓离子 N2H+）的高分辨率 NEXAFS 光谱。通过从头计算，我们表明该光谱由两个氮 1s 吸收光谱的叠加组成，每个吸收光谱包括一个 π* 带和一个氮 1s 到 H+ 电荷转移带，后面是弱的不规则级数的高能激发。计算还表明，由于质子化对称性破缺的影响，π* 跃迁相距 0.23 eV，仅略超过中性 N2 相应的暗（禁止对称）和亮（允许对称）核心激发的差异。通过 DFT、计算和振动分析，N2H+ 的复杂 π* 激发带被理解为是由于末端和中心氮原子激发的显着不同的振动级数的叠加，两者都会导致弯曲的最终状态几何形状。我们还通过计算表明，电荷转移激发的电子结构平稳地取决于氮-质子距离，并且光谱从无穷大到接近的氮-质子距离有明显的延伸，其中精细结构显示出一些虽然不完全详细的相似性。氮核心轨道部分局域化的一个有趣特征是，随着氮-质子距离的变化，具有强烈的、非单调的变化。当比较分子阳离子 NEXAFS 光谱（以最近记录的 N2+ 和 CO+ 光谱为代表）和质子化分子的光谱（以 N2H+ 离子代表）时，可以揭示具体的影响。由于带正电荷，这两种类型都包含中性分子 NEXAFS 中未体现的丰富物理效应，而质子化也会破坏对称性。质子化对二氮的影响可以在电荷（扩展光谱的高能部分）和对称破缺（在低能 π* 跃迁中最明显）方面分开。
As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion N2H+. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π* band, and a nitrogen 1s to H+ charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π* transitions are separated by 0.23 eV, only slightly exceeding the difference in the corresponding dark (symmetry forbidden) and bright (symmetry allowed) core excitations of neutral N2. By DFT and calculations and vibrational analysis, the complex π* excitation band of N2H+ is understood as due to the superposition of the significantly different vibrational progressions of excitations from terminal and central nitrogen atoms, both leading to bent final state geometries. We also show computationally that the electronic structure of the charge transfer excitation smoothly depends on the nitrogen–proton distance and that there is a clear extension of the spectra going from infinity to close nitrogen–proton distance where fine structures show some, although not fully detailed, similarities. An interesting feature of partial localization of the nitrogen core orbitals, with a strong, non-monotonous, variation with nitrogen–proton distance could be highlighted. Specific effects could be unraveled when comparing molecular cation NEXAFS spectra, as represented by recently recorded spectra of N2+ and CO+, and spectra of protonated molecules as represented here by the N2H+ ion. Both types containing rich physical effects not represented in NEXAFS of neutral molecules because of the positive charge, whereas protonation also breaks the symmetry. The effect of the protonation on dinitrogen can be separated in charge, which extends the high-energy part of the spectrum, and symmetry-breaking, which is most clearly seen in the low-energy π* transition.