Two rotational isomers of resorcinol . CO were investigated using zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Vibrational progressions and combination bands of the in-plane-bend, stretch and in-plane-wag intermolecular modes were observed in the spectra of each isomer. While the frequencies of these intermolecular modes were similar for both isomers, the Franck-Condon patterns for vibrational excitation were notably different, indicating that the isomers experience distinctive geometry changes upon ionization. Ab initio calculations at the MP2/6-31G* level of theory predict the existence of many stable isomers of resorcinol . CO, with the three lowest energy minima corresponding to structures where the CO molecule binds through its carbon atom to one OH group of resorcinol. The calculations were used to assign the vibrational features in the ZEKE spectra and distinguish the rotational isomers observed.