Mass-Correlated High-Resolution Spectra and the Structure of Benzene

Mass-correlated rotational alignment spectroscopy resolved the rotational Raman spectra for 5 benzene isotopologues with unprecedented resolution. 13-C isotopologues were characterized at natural abundance. Fitted rotational constants allowed the analysis of effective and equilibrium bond lengths for benzene with sub-mÅ uncertainties. We found that previously reported experimental structures were wrong by multiple mÅ, due to unrecognized H/D isotope effects. Our results also refute recent experimental and theoretical literature claims of identical effective C–H and C–D bond lengths in benzene and reveal an isotope effect similar to that in other small molecules.质量关联旋转对齐光谱法（Mass-correlated rotational alignment spectroscopy）以空前分辨率解析了5种苯同位素异构体的转动拉曼光谱。以天然同位素丰度对13-C同位素异构体完成了表征。通过拟合得到的转动常数，可对苯的有效键长与平衡键长开展分析，其不确定度低至亚毫埃（sub-mÅ）级。研究发现，此前报道的苯分子实验结构存在多达数毫埃的误差，其根源在于未被识别的氢氘（H/D）同位素效应。本研究结果同时驳斥了近期文献中关于苯分子内C-H与C-D有效键长一致的实验与理论论断，并揭示了与其他小分子相似的同位素效应。