Abstract

Time-resolved S„-S-i resonance spontaneous Raman spectra of chrysene in tetrahydrofuran were observed for the first time together with T„- T| resonance Raman spectra by using ultrapure samples. The electronic excitation was performed by the third harmonic of a O-switched Nd:YAG laser, and the Raman probe was dye- laser-pumped by the second harmonic of the Nd:YAG laser. We could observe the Raman lines attributed to the S-ι state at 1549, 1369, 1344, 1110, and 990 cm^-1. Those attributed to the T-, state were observed at 1528, 1494, 1353, 1199, 1110, 990, 678, 554, 472, and 286 cm“¹. The decay time constant of the 1369-cm“¹ integrated intensity (S-ι) line, the formation time constant of the 1528-cm^-1 (T-,) line, that of the 1199-cm“¹ (T-,) line, and the fluorescence lifetime were found to be + 6 35 ns, - 5 + 19 51 ns, - 12 + 10 41 ns, and 41 ± 1 ns, - 7 respectively. The geometrical changes in the excited states were considered using the observed Raman shift wave numbers on the assumption that the changes were small for the rigid molecular structure; we came to the following conclusions: (1) The geometry of the resonance-coupled excited singlet state and that of the ground state mainly differ along the normal coordinates of the vibrational modes observed in the S„-Si resonance Raman spectra at 1549 and 1344 cm^-1. (2)The geometrical differences between the resonance-coupled excited triplet state and the ground state are mainly along the coordinates of the modes observed in the T„-T-¡ resonance Raman spectra at 1528, 1353, 1110, and 990 cm“¹ and that observed In the Shpolskii spectrum of phosphorescence at 1385 cm^-1 by Jung et al. (3) The excited singlet and triplet states differ along the normal coordinates of the vibrational modes observed in the T_n-T, resonance Raman spectra at 678, 554, 472, and 286 cm“¹. (Poster paper)

© 1986 Optical Society of America