LIF and IR Dip Spectra of Jet-Cooled p-Aminophenol−M (M = CO, N2): Hydrogen-Bonded or Van der Waals-Bonded Structure?

Abstract

Intermolecular interaction and stable structures of the p-aminophenol-M (M=CO, N 2 ) 1:1 complexes have been studied by measuring the S 1 ← S 0 (ππ * ) fluorescence excitation spectra and the IR dip spectra in the OH and NH stretch region combined with ab initio calculations. The S 1 -S 0 electronic origin of the CO complex is 141 cm - 1 red shifted from the origin of the monomer. The red shift for the CO complex is smaller than 153 cm - 1 for the N 2 complex, although the molecular polarizability of carbon monoxide is larger than that of molecular nitrogen. The OH stretching frequency of the CO complex is 26 cm - 1 red shifted from that of the monomer in the IR dip spectrum, but the N 2 complex shows no shift. On the basis of these findings we conclude that carbon monoxide is bonded to the OH group via a hydrogen bond, whereas nitrogen is van der Waals-bonded to the π cloud of the aromatic ring.