Infrared Depletion Spectroscopy of the Aniline Dimer

The infrared depletion spectrum of the aniline dimer, formed in a supersonic jet, has been recorded in the N−H stretch region by combining infrared laser excitation and resonant two-photon ionization/time-of-flight mass spectrometry. Only two bands have been found at 3394.0 and 3465.9 cm-1 (±0.5 cm-1) in the region 3130−3530 cm-1. These are red-shifted by 27.8 and 42.3 cm-1 from the symmetric and asymmetric NH stretching vibrations of the aniline monomer, respectively. A configuration with mutual NH2···π bonds and phenyl groups stacked in parallel is suggested for the ground-state aniline dimer.