Abstract:
Infrared (IR) photodissociation spectra of the aniline+-Arn cations, An + - Ar n (n = 1, 2), are analyzed in the vicinity of the N-H stretch fundamentals. The complexes are produced in an electron impact (EI) ion source which produces predominantly the most stable cluster isomers. Two isomers of An+-Ar are identified by their characteristic N-H stretch frequencies: the planar proton-bound global minimum, in which the Ar ligand forms a nearly linear H-bond to the amino group, and the less stable π-bound local minimum, in which the Ar atom is attached to the π-electron system of the aromatic ring. This result is the first unambiguous detection of the most stable H-bound An+-Ar dimer. All previous spectroscopic studies of An+-Ar employed resonance enhanced multiphoton ionization (REMPI) of neutral An-Ar and identified only the less stable π-bound cation due to restrictions arising from the Franck-Condon principle. The EI-IR spectrum of An+-Ar2 shows that the most stable structure of this trimer features two equivalent H-bonds (C2v symmetry). The interpretation of the experimental data is supported by quantum chemical calculations. The ab initio potential of An+-Ar calculated at the UMP2/6-311G(2df, 2pd) level features H-bound global minima ( D e = 513 cm-1) and π-bound local minima ( D e = 454 cm-1), with a barrier of V b ≈ 140 cm-1 for isomerization from the π-bound toward the H-bound minimum.
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Received 4 February 2002 Published online 13 September 2002
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Solcà, N., Dopfer, O. Interaction between aromatic amine cations and nonpolar solvents: Infrared spectra of isomeric aniline -Ar n ( ) complexes. Eur. Phys. J. D 20, 469–480 (2002). https://doi.org/10.1140/epjd/e2002-00147-6
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DOI: https://doi.org/10.1140/epjd/e2002-00147-6