Knowledge Bank

The fluorescence excitation spectra (FES), dispersed fluorescence (SVLF) spectra, and ultraviolet absorption spectra of 1,2-dihydronaphthalene have been collected and analyzed. The $S1(\pi ,\pi \ast )$ electronic band origin is at $34,096cm-1$. The FES for the jet-cooled molecules shows the four lowest frequency vibrations in the $S1$ state to be at 107, 122, 197, and $293cm-1$; while the SVLF from several excitation bands shows these to be at 131, 149, 267 and $347cm-1$ in the $S0$ state. For both states almost all of the transition frequencies below $800cm-1$ can be assigned as combinations of these low-frequency modes. The series of bands beginning with $131cm-1$ for $S0$ and $122cm-1$ for $S1$ were analyzed to determine the ring-twisting potential energy functions. For the $S0$ state the barrier of about $1300cm-1$ is somewhat higher than that ($1132cm-1$) for the analogous molecule 1,3-cyclohexadiene. For the $S1$ state the barrier increases significantly.