Microsolvation of aniline+–Arn (n=1–21) cluster cations investigated by infrared depletion spectroscopy

The infrared spectra of the NH2 stretching vibrations of aniline+–Arn (n=1–21) cluster cations have been measured by the depletion method. Aniline+–Arn clusters were prepared by near-resonant resonance-enhanced multiphoton ionization (REMPI) of larger aniline–Arm clusters. The red shifts of the NH stretching vibrations were 17–25 cm−1, depending on the cluster size. The spectra of small clusters showed that there were hydrogen-bond-type (NH–Ar) and dispersion-type (Ar–π) isomers and that the NH–Ar isomer was more stable. The red shifts of the NH2 stretching vibrations varied with the number of Ar atoms and showed a maximum at n=12 and a local minimum at n≈19.