S. Hogiu et al., Vibrational analysis and excited-state geometric changes of betaine-30 derived from Raman and infrared spectra combined with ab initio calculations, J RAMAN SP, 31(8-9), 2000, pp. 797-803
We present a combined experimental and theoretical study of vibrational mod
es and excited-state geometry changes of betaine-30 (B-30). Infrared and Ra
man spectra were recorded under electronic off-resonant excitation conditio
ns and also in resonance with the charge transfer transition of B-30, Compa
ring these spectra with the corresponding vibrational patterns calculated b
y Hartree-Fock methods we obtained the assignments of the vibrational modes
, Excited-state geometry changes were calculated for a smaller model system
of B-30 using configuration interaction with single excitations. The calcu
lations predict that the central phenoxide and pyridinium rings move from a
twisted conformation in the electronic ground state into a perpendicular p
osition in the first excited state. In addition, the pyridinium ring tilts
and the nitrogen atom becomes pyramidalized, In correspondence, we measured
two strong low-wavenumber Raman bands with large origin shifts at 291 and
133 cm(-1). They were assigned to N-inversion and torsional vibrational mod
es and are expected to mediate the excited state and back-electron transfer
reaction of B-30, Copyright (C) 2000 John Wiley & Sons, Ltd.