The 4-aminobenzonitrile chromophore (ABN), has two active sites for solvation with water and the ABN(H2O)(1) complex a number of isomers of similar stability, as revealed by ab initio calculations conducted by DFT and MP2 methods. Hole burning and two-colour mass-resolved spectroscopies provide evidence on the presence of two isomers in the ABN(H2O) complex. The identification of the observed isomers to calculated structures has been carried out by comparison between the appropriate spectra and the ab initio calculated ionization energies (IEs) and the experimental and simulated rotational contours. Stability arguments are useless owing to the close isomer dissociation energies. (C) 2002 Published by Elsevier Science B.V.