The two-color zero-kinetic-energy (ZEKE) photoelectron spectra of naphthalene are simulated and analyzed by means of quantum-chemical calculations of molecular parameters followed by the modeling of vibronic intensities. Ab initio and semiempirical calculations are carried out to obtain molecular structures of the initial S-1 and final D-0 states of neutral and ionic naphthalene, respectively. The vibronic perturbations that couple these states to low-lying excited states are also evaluated and included in the model based on the perturbative expansion of vibronic states. It is shown that the simulated intensities reproduce the observed spectra in a very satisfactory fashion. The most prominent bands are identified and some reassignments of ground state frequencies of the cation are indicated on the basis of simulated vibronic intensities. This is, to date, the first completely theoretical simulation of ZEKE spectra of a medium-large molecule based on a model which goes beyond the usually assumed Franck-Condon selection rules. (C) 1997 American Institute of Physics.