The fluorescence excitation spectra, single vibrational level fluorescence spectra, and ultraviolet absorption spectra of 1,4-dihydronaphthalene have been analyzed. The first four quantum energy spacings for the ring-puckering vibration were determined for the S-0 and S-1(pi, pi*) electronic states, and the potential energy functions were also determined. In the ground state the single-minimum function is dominated by the quartic term, but in the excited state the function becomes nearly harmonic. The S-0 function is less rigid than that for 1,4-cyclohexadiene but the S-1(pi, pi*) function becomes much more rigid. Earlier work on this molecule had erroneously postulated barriers in both electronic states. (c) 2007 Elsevier B.V. All rights reserved.