Fluorescence and ultraviolet absorption spectra, and the structure and vibrations of 1,2,3,4-tetrahydronaphthalene in its S1(π,π*) state

The ultraviolet absorption spectra in the static vapor phase and the laser induced fluorescence spectra (both fluorescence excitation and single vibronic level fluorescence spectra) of jet-cooled 1,2,3,4-tetrahydronaphthalene have been used along with theoretical calculations to assign many of the vibronic levels in the S-1(pi,pi*) state. These have been compared to the corresponding vibrational levels for the S-0 ground state. Analysis of the upper states of the ring-twisting vibration nu(31) and three other low-frequency modes has allowed us to construct an energy map of the lowest vibrational quantum states for both S-0 and S-1. The molecule is highly twisted in both electronic states with high barriers to planarity, which are calculated to be 4811 cm(-1) for S-0 and 5100 cm(-1) for S-1. However, the experimental data show that the barrier should be lower in the S-1 state.