Soliton spin density in polyacetylene studied by endor in pristine and 13C-enriched cis-rich sample

Abstract

ENDOR measurements were performed on pristine and 13C-enriched undoped cis -rich (CH) X down to 4K. Temperature dependence of the spectra in 13C-enriched system revealed that the structures observed at higher temperatures, which were formerly assigned to proton or 13C hyperfine tensor components by Thomann et al. , grow into sharp single resonance lines as the temperature is lowered. The frequencies of those lines have been found to be related to proton and 13C nuclear frequencies. For example, the structure around 7.3 MHz, which was assigned to a 13C tensor component, is the second harmonic of 13C nuclear frequency. Comparison of the spectra between pristine and 13C-enriched system clearly showed that the intrinsic spin density of the soliton, confirmed by our previous ENDOR analysis in pristine system, is not observable in the latter system because of the line shape distortion due to the overlapping of those structurs due to nuclear frequencies.