The 1:1 complex of p-cyanophenol and water (CNP-W-1) formed in the supersonic jet was studied using fluorescence excitation, REMPI, hole-burning, and fluorescence detected IR (FDIR) spectroscopy. Only one out of the five possible CNP-W-1 conformers was identified experimentally using hole-burning spectroscopy. The observed conformer was assigned to the one in which CNP acts as the proton donor from the spectroscopic results and the calculations. The observed red shift of the band origin and the reduction in the OH frequency correlates well with the pK(a) of the monomer in the ground and the excited state. (C) 2004 Elsevier B.V. All rights reserved.