The hydrogen-bonded and van der Waals isomers of phenol .. nitrogen and phenol .. carbon monoxide in their neutral electronic (S-0) and cation ground state (D-0) were studied using ab initio HF/6-31G*, MP2/6-31G*, and B3LYP/6-31G* methods. The hydrogen-bonded isomers have the ligand bound via the hydroxyl group of the phenol ring, while the van der Waals isomers studied have the ligand located above the aromatic ring. For both complexes, the hydrogen-bonded isomer was found to be the most stable form for both the S-0 and the D-0 states. For phenol .. carbon monoxide, twice as many isomers as compared to phenol .. nitrogen were found. The hydrogen-bonded isomer with the carbon end bonded to the hydroxyl group was the most stable structure for both the S-0 and the D-0 states.