This report presents the results of measurements of transmission and reflexion spectra of polyacetylene films in the infrared range 4-25 μm. [CH(I3-) Y]x samples were used with various thickness for iodine doping level Y up to 0.07. We used a high detectivity spectrometer which permitted us to obtain spectra with very highly doped free-standing films. In this way, we could measure both the relatively large thicknesses of samples with accuracy and also directly measure the doping level by weight uptake. The results show that, although intrafibril doping is nonuniform, the material is quite isomerized. In addition, our analysis demonstrates that the ω 2 band (900 cm-1) induced upon doping cannot be the pinned mode.