The laser-induced fluorescence spectra and dispersed fluorescence spectra of jet-cooled 1,2-dihydronaphthalene have been analyzed to investigate the ring inversion process in both the S-0 and S-1(pi,pi(*)) excited states. Ultraviolet absorption, infrared, and Raman spectra were also recorded to complement the analyses. Ab initio calculations predict the inversion process to involve four out-of-plane ring motions, and linear combinations of these were made to model the inversion process. The data show the barrier to inversion in the ground state to be 1363+/-100 cm(-1) (the triple-zeta ab initio value is 1524 cm(-1)). The experimental data indicate that the barrier increases substantially in the excited state, for which the calculated barrier is 1526 cm(-1) with a CIS/6-311+G(d) basis set. (C) 2003 American Institute of Physics.