Abstract: Resonance Raman spectra of I₂-cyclohexene charge-transfer complex were obtained with three excitations at ～300 nm absorption band of the complex. Density functional theory calculations were carried out to examine the structure and normal mode frequencies of the ground state of the complex and its electronic transition energies. The strong absorption band around 300 nm was assigned to p_z (I17)→ π^*(C=C) transition,that is the transition of a p_z electron from I atom at C=C terminal to anti-bonding orbital of C=C double bond. The resonance Raman spectra displayed the Raman intensity in the overtones and combination bands of the nominal I—I stretch and C=C stretch modes.This suggested that the complex underwent an obvious valence change in both I—I and C=C.

Key words: Charge-transfer complex, Resonance Raman spectrum, Absorption spectrum, Density functional theory