APPLICATION OF TIME-DEPENDENT RAMAN THEORY TO RAMAN EXCITATION PROFILES OF HEXAMETHYLBENZENE-TETRACYANOETHYLENE ELECTRON-DONOR ACCEPTOR COMPLEX

Raman excitation and absorption profiles were obtained for the 1:1 ele ctron donor-acceptor complex of hexamethylbenzene with tetracyanoethyl ene in dichloromethane solution, The absorption and Raman profiles wer e analyzed using the time-dependent theory of Heller to obtain the dis placements and non-Condon factors for the four strongest Raman modes, the electronic excitation energy, the transition dipole, and solvent l ine-broadening parameters. The results are compared to the data report ed by Myers et al (J, Am. Chem, Sec. 1992, 114, 6208) for the same com plex in carbon tetrachloride solution. Attempts to account for solvent effects on the normal-mode displacements in terms of the solvent loca l field lead are complicated by the effect of the solvent on the struc ture of the complex, We propose that in CH2Cl2 but not in CCl4, the co mplex adopts a low-symmetry ground-state geometry which permits vibron ic coupling of the charge-transfer and locally excited (TCNE) states.