Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA.
J Phys Chem A. 2012 Oct 4;116(39):9689-95. doi: 10.1021/jp307631n. Epub 2012 Sep 20.
Protonated pyrrole cations are produced in a pulsed discharge/supersonic expansion source, mass-selected in a time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy. Vibrational spectra in both the fingerprint and C-H/N-H stretching regions are obtained using the method of tagging with argon. Sharp vibrational structure is compared to IR spectra predicted by theory for the possible α-, β-, and N-protonated structures. The spectral differences among these isomers are much larger than the frequency shifts due to argon attachment at alternative sites. Though α-protonation predominates thermodynamically, the kinetically favored β-protonated species is also observed for the first time (in 3-4 times lower abundance under the conditions employed here). Theoretical investigations attribute the greater stability of α-protonated pyrrole to topological charge stabilization, rather than merely to the greater number of resonance contributors. The far-IR pattern of protonated pyrrole does not match the interstellar UIR bands.
质子化吡咯阳离子在脉冲放电/超音速膨胀源中产生，在飞行时间光谱仪中进行质量选择，并通过红外光解离光谱进行研究。使用氩标记的方法获得指纹区和 C-H/N-H 伸缩区域的振动光谱。将锐化的振动结构与理论预测的可能的 α-、β-和 N-质子化结构的 IR 光谱进行比较。这些异构体之间的光谱差异远大于由于在替代位置上与氩结合而引起的频率位移。尽管热力学上α-质子化占优势，但动力学上有利的β-质子化物种也首次被观察到（在本文所采用的条件下，丰度低 3-4 倍）。理论研究将α-质子化吡咯的更高稳定性归因于拓扑电荷稳定化，而不仅仅是共振贡献者的数量更多。质子化吡咯的远红外模式与星际 UIR 带不匹配。
