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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopic identification of carbenium and ammonium isomers of protonated aniline (AnH(+)): IR spectra of weakly bound AnH(+)-L-n clusters ( L = Ar, N-2)
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Spectroscopic identification of carbenium and ammonium isomers of protonated aniline (AnH(+)): IR spectra of weakly bound AnH(+)-L-n clusters ( L = Ar, N-2)

机译：质子化苯胺（AnH（+））的碳铵和铵异构体的光谱鉴定：弱键合的AnH（+）-L-n簇（L = Ar，N-2）的红外光谱

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摘要

Infrared photodissociation (IRPD) spectra of mass-selected clusters composed of protonated aniline (C6H8N+) = AnH(+)) and a variable number of neutral ligands (L = Ar, N-2) are obtained in the N-H stretch range. The AnH(+)-L-n complexes (n <= 3) are produced by chemical ionization in a supersonic expansion of An, H-2, and L. The IRPD spectra of AnH(+)-L-n feature the unambiguous fingerprints of at least two different AnH(+) nucleation centers, namely, the ammonium isomer (5) and the carbenium ions (1 and/or 3) corresponding to protonation at the N atom and at the C atoms in the para and/or ortho positions, respectively. Protonation at the meta and ipso positions is not observed. Both classes of observed AnH(+)-L-n isomers exhibit very different photofragmentation behavior upon vibrational excitation arising from the different interaction strengths of the AnH(+) cores with the surrounding neutral ligands. Analysis of the incremental N-H stretch frequency shifts as a function of cluster size shows that microsolvation of both 5 and 1/3 in Ar and N-2 starts with the formation of intermolecular H bonds of the ligands to the acidic NH protons and proceeds by intermolecular pi bonding to the aromatic ring. The analysis of both the photofragmentation branching ratios and the N-H stretch frequencies demonstrates that the N-H bonds in 5 are weaker and more acidic than those in 1/3, leading to stronger intermolecular H bonds with L. The interpretation of the spectroscopic data is supported by density functional calculations conducted at the B3LYP level using the 6-31G* and 6-311G(2df, 2pd) basis sets. Comparison with clusters of neutral aniline and the aniline radical cation demonstrates the drastic effect of protonation and ionization on the acidity of the N-H bonds and the topology of the intermolecular potential, in particular on the preferred aromatic substrate-nonpolar ligand recognition motif.
机译：在N-H拉伸范围内获得了由质子化苯胺（C6H8N +）= AnH（+）和可变数目的中性配体（L = Ar，N-2）组成的质量选择簇的红外光解离（IRPD）光谱。 AnH（+）-Ln络合物（n <= 3）是通过化学电离在An，H-2和L的超音速膨胀中产生的。AnH（+）-Ln的IRPD光谱至少具有清晰的指纹两个不同的AnH（+）成核中心，即铵异构体（5）和碳正离子（1和/或3），分别对应于对位和/或邻位N原子和C原子的质子化。没有观察到在meta和ipso位置的质子化。观察到的两类AnH（+）-L-n异构体在振动激发后均表现出非常不同的光碎化行为，这是由于AnH（+）核与周围中性配体的不同相互作用强度引起的。分析NH增量拉伸频率增量随簇大小变化的关系，表明Ar和N-2中5和1/3的微溶剂化都始于配体与酸性NH质子的分子间H键的形成，并通过分子间进行π键键合到芳环上。对光碎化分支比和NH延伸频率的分析表明，5个中的NH键比1/3中的NH键更弱和更酸，从而导致与L的分子间H键更强。光谱数据的解释得到以下支持使用6-31G *和6-311G（2df，2pd）基集在B3LYP级别上进行密度函数计算。与中性苯胺和苯胺自由基阳离子簇的比较表明，质子化和电离对N-H键的酸度和分子间电势的拓扑，特别是对优选的芳香族底物-非极性配体识别基序的影响很大。

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