Kappe Miriam, Schöpfer Gabriel, Schiller Arne, Gruber Elisabeth, Ončák Milan, Ellis Andrew M, Scheier Paul
Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria.
Institute for Breath Research, Universität Innsbruck, Innrain 66, A-6020 Innsbruck, Austria.
Phys Chem Chem Phys. 2025 Oct 8;27(39):21150-21156. doi: 10.1039/d5cp03392f.
An optical spectrum of the singly charged anionic dimer of C, the C anion, is reported for the first time. This spectrum, recorded in the mid-infrared and extending from 800 cm through to 2200 cm, shows a mixture of discrete peaks and broader features. An assignment of this spectrum poses a major challenge for theory. A broad feature observed above 1600 cm can be unambiguously assigned to one or many electronic transitions. However, it is not clear which isomer is responsible for it, as many isomers show electronic transitions in this spectral range. The origin of peaks below 1600 cm in the experimental spectrum remains uncertain, as calculations predict both electronic and vibrational transitions in this spectral range for various isomers. The proximity of several electronic and vibrational transitions suggests a breakdown of the Born-Oppenheimer approximation. This suspicion is supported by the fact that the vibrational spectrum is very dependent on the computational method, much more than expected for small molecules in the gas phase. All in all, C seems to be at the brink of what is computationally feasible with current methods of quantum chemistry. We also report mid-IR spectra for the larger cluster anions, C and C, whose spectra show significant similarities to that of C.
首次报道了碳的单电荷阴离子二聚体（C⁻阴离子）的光谱。该光谱在中红外波段记录，范围从800厘米⁻¹延伸至2200厘米⁻¹，呈现出离散峰和较宽特征的混合。对该光谱进行归属对理论而言是一项重大挑战。在1600厘米⁻¹以上观察到的一个宽特征可以明确归属于一个或多个电子跃迁。然而，尚不清楚是哪种异构体导致了该特征，因为许多异构体在这个光谱范围内都显示出电子跃迁。实验光谱中1600厘米⁻¹以下峰的起源仍然不确定，因为计算预测各种异构体在这个光谱范围内既有电子跃迁也有振动跃迁。几个电子跃迁和振动跃迁的接近表明了玻恩 - 奥本海默近似的失效。振动光谱对计算方法的依赖性很强这一事实支持了这种怀疑，其依赖性远超气相中小分子的预期。总而言之，用当前量子化学方法计算C⁻似乎已接近可行极限。我们还报道了更大团簇阴离子C₃⁻和C₄⁻的中红外光谱，它们的光谱与C⁻的光谱显示出显著相似性。
