The potential energy surfaces of PhOH-(NH3)(0,1) and NH4(NH3)(1-4) have been investigated theoretically by ab initio methods. Intermolecular stretching in PhOH-NH3 assists in the radical cleavage of an OH bond occurring through a pipi*/pisigma* potential crossing. Thus, excited state hydrogen transfer (ESHT) is expected to take place by a solvent-assisted mechanism even in the larger PhOH-(NH3)(n). Because sufficient energy is obtained by ESHT from PhOH-(NH3)(n) (pipi(*)) to PhO-NH4(NH3)(n-1) (pisigma(*)) (nless than or equal to5), hydrogen relocation and/or ammonia migration in the product NH4(NH3)(n-1) can readily follow ESHT, which is responsible for observing isomer bands in the absorption spectra of the photoinduced reaction products of PhOH-(NH3)(n). (C) 2003 American Institute of Physics.