The polarized Raman and infrared spectra of θ-(ET) 2 Cu 2 CN[N(CN) 2 ] 2 [ET = bis(ethylenedithio) tetrathiafulvalene] were measured at various temperatures below 300 K. We investigated the three C=C stretching modes, ν 2 , ν 3 and ν 27 . The spectral pattern is compatible with the horizontally charge-ordered state, where the site-charge distributions are +0.1 7 and +0.8 3 . We have found that the vibronic ν 3 bands correlate to the dihedral angles, φ, in the θ-ET salts. This relation is well reproduced by the numerical calculation based on the cluster model with C 2 symmetry. The spectral features suggest the dynamical fluctuation of nearly localized charges even above its phase transition temperature, ∼220 K. © 2004 The Physical Society of Japan.