The van der Waals vibrational frequencies of the aniline-carbon monoxide complex in its S 1 state

Abstract

A portion of the S 1-S 0 band of the aniline-CO van der Waals (vdW) complex has been observed near 297 nm, using REMPI/TOF spectroscopy. Compared to the same band in aniline itself, this represents a shift to longer wavelengths of over 300 cm −1, which is one of the largest red shifts so far observed for this type of vdW complex. The spectrum observed consisted of five almost equally intense, relatively sharp sub-bands and we have assigned these as the O 0 0 bands plus four signals arising from transitions to vibrational levels in the S 1 state which are associated with the van der Waals bond. In order to account for these four sub-bands, it appears that transitions to a minimum of three different vdW vibrational modes are required. Two signals appear to involve the first and second level of the same vibration, the other two seem to arise from at least a further two different vibrational levels. The large values of both the red shift of the S 1-S 0 band and the frequencies of the vdW modes indicate that aniline-CO is a relatively strongly bonded complex. It was concluded that the CO molecule probably lies in the symmetry plane above the aromatic ring of the aniline molecule.