Abstract: Fe K absorption spectra of an electrically conductive polymer——FeCl_3-doped polythiophene and model compound [N(C_2H_5)_4][FeCl_4] were measured with a laboratory EXAFS system, which utilizes a high power rotating-anode X-ray generator (Rigaku model RU-1000) as a X-ray source. The analysis of observed EXAFS data shows that Fe atom is surrounded by four Cl atoms with Fe-Cl distance of 2.19. It is concluded that the dopant exists mainly in the form of FeCl_4~-. The result provides a direct structural information that strongly supports the proposition: the doping process is as follows
2FeCl_3+e~-→FeCl_4~-+FeCl_2