Laser-Induced Fluorescence Spectra and Torsional Potential Energy Functions of Jet-Cooled 4,4‘-Dimethyl-trans-Stilbene

Spectroscopic investigation of the molecular vibrations of 1,4-dihydronaphthalene in its ground and excited electronic States

A comprehensive spectroscopic study of 1,4-dihydronaphthalene (14DHN) has been carried out for its ground and S(1)(pi,pi*) electronic states using infrared, Raman, ultraviolet, and laser-induced fluorescence (LIF) spectroscopic techniques. The experimental work was complemented by ab initio and DFT calculations. For the ground state excellent agreement between observed and calculated values was attained. For the S(1)(pi,pi*) excited state 19 of the vibrational modes were clearly determined and excited vibronic levels for a number of these were also identified. A detailed energy map for the low-frequency modes in both electronic states was established. 14DHN is very floppy in its S(0) ground state but less so in its excited state. The floppiness relaxes C(2v) selection rules for the S(0) state.

Laser-Induced Fluorescence Spectra, Structure, and the Ring-Twisting and Ring-Bending Vibrations of 1,4-Benzodioxan in Its S0 and S1(π,π*) States

The laser-induced fluorescence (LIF) spectra, both the fluorescence excitation spectra (FES) and single vibrational level fluorescence spectra (SVLF) from several different vibronic states, along with the ultraviolet (UV) absorption spectra of 1,4-benzodioxan have been recorded and analyzed. A detailed energy map has been constructed for four low-frequency vibrations and their combinations for both the S(0) and S(1)(pi,pi) electronic states. These are nu(48) (ring-bending), nu(25) (ring-twisting), nu(47) (ring-flapping), and nu(24) (skeletal-twisting). Both the experimental and ab initio calculations show the molecule to be twisted in both the S(0) and S(1)(pi,pi) states with high barriers to planarity. The experimentally determined ring-twisting quantum states, which are confined to the lower regions of the potential energy surface, were used to calculate one-dimensional potential functions in terms of the twisting coordinates, and the extrapolated barriers were estimated to be 5700 and 4200 cm(-1) for the S(0) and S(1) states, respectively. Two-dimensional calculations, which included the interactions with the bending modes, gave values of 3906 and 1744 cm(-1), respectively. The S(0) value compares favorably with the ab initio value of 4095 cm(-1).