Polarized X-ray absorption spectra of halogen-doped polyacetylene

Abstract

The local structure and chemical states of halogens doped in stretch-oriented trans -polyacetylene are studied by polarized X-ray absorption spectroscopy. Polarized EXAFS and near-edge spectra are measured for (CHBr y) x and (CHI y) x on the Br K- and I L-edges over a wide range of dopant concentration. The Fourier transform of EXAFS oscillations for (CHBr y) x indicate that in the lightly doped region (0.01<y<0.2), polybromine ions are formed which are highly oriented along the c-axis while bromines also form covalent bonds with (CH) x which increases on going to heavily doped region (y>0.2). It is expected that bromines are incorporated as isolated ions in the early stage of doping (y<0.01). The Fourier transform analysis (CHI y) x indicate that iodines form also polyions which are chemically less reactive.