The infrared spectra of the NH2 stretching vibrations of aniline–toluene cluster and corresponding cluster cation have been measured by the infrared depletion method. The NH2 stretching vibrations of aniline–toluene cluster were observed at 3393 and 3468 cm−1. The red shifts from the corresponding bands of aniline monomer are 29 and 40 cm−1, respectively, for the NH2 symmetric and anti-symmetric stretching vibrations. The magnitudes of the red shifts are similar to those of other aniline–aromatic clusters. The structure of this cluster has been found to be a sandwich type, that is, the two aromatic rings are parallel in the cluster and main interaction forces are the NH2–π type hydrogen bond and the dispersion force between two aromatic rings. The reason for the constant red shift for the different clusters with different proton affinity has been discussed.
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