THE VAN-DER-WAALS VIBRATIONAL FREQUENCIES OF THE ANILINE-CARBON MONOXIDE COMPLEX IN ITS S-1 STATE

A portion of the S-1-S-0 band of the aniline-CO van der Waals (vdW) co mplex has been observed near 297 nm, using REMPI/TOF spectroscopy. Com pared to the same band in aniline itself, this represents a shift to l onger 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 obse rved consisted of five almost equally intense, relatively sharp sub-ba nds and we have assigned these as the 0(0)(0) band plus four signals a rising from transitions to vibrational levels in the S-1 state which a re associated with the van der Waals bond, In order to account for the se four sub-bands, it appears chat transitions to a minimum of three d ifferent vdW vibrational modes are required. Two signals appear to inv olve the first and second level of the same vibration, the other two s eem 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 fr equencies of the vdW modes indicate that aniline-CO is a relatively st rongly bonded complex, It was concluded that the CO molecule probably lies in the symmetry plane above the aromatic ring of the aniline mole cule.