Structures and vibrations of p-dimethoxybenzene conformers in the S-0 and S-1 states studied by ab initio calculations and resonant two-photon ionization spectroscopy

摘要

Detailed data on the structures and vibrations of the p-dimethoxybenzene (PDMB) conformers in the S-0 and S-1 states have been obtained by ab initio calculations and resonant two-photon ionization (R2PI) spectroscopy. Results from optimized geometry calculations show that several conformers (assuming the methoxyl groups are a point) exist in the So state. However, only the cis and trans planar conformers appear as stable species in the S-1 state. The S-1<--S-0 transition causes the ring to expand and the ring C-OCH3 bond to shrink, indicating an enhanced interaction between the ring and the methoxy substituent of PDMB in the excited state. The R2PI spectrum displays two series of bands with respect to the two band origins separated by 221 cm(-1).These features can be well correlated to the cis and trans conformers involved in the electronic excitation. Computed results on normal vibrational frequencies also enable us to assign the spectral bands observed. (C) 1998 Elsevier Science B,V. All rights reserved. [References: 28]