Resonant Raman scattering of polymeric sulfur nitride modified by iodine

Resonance Raman spectra of (SNI_y)_x crystals have been measured at 150 K. The energies of the principal Raman lines of the chromophore (109 and 154 cm^?1) and their intensity behaviour with exciting laser frequency are consistent with the formation of a charge-transfer complex in which iodine enters the interfiber regions of the (SN)_x lattice as I₅^- or I₃^- linked to distorted I₂ units. This structural model is supported by comparison of these Raman data with the excitation profiles of the chromophoric group in starch-iodine and α-cyclodextrine-iodine complexes. Possible mechanisms for the conductivity increase on the basis of the proposed charge transfer model are also discussed.