Electron-Nuclear Double Resonance Studies of Pristine and ¹³C-Enriched Polyacetylene

Abstract

Electron-nuclear double resonance (ENDOR) and electron-nuclear-nuclear triple resonance (TRIPLE) spectra of pristine cis-rich (CH)_x at low temperatures are consistent with the spin density distribution of the soliton predicted for a finite electron correlation. The ratio of the peak value of the negative spin density ρ(1) to that of the positive spin density ρ(0) is determined to be ρ(1)⁄ρ(0)∼−0.44 with the aid of ENDOR-induced ESR measurements. On the other hand, intrinsic ENDOR spectra due to the soliton spin density is not observable in ¹³C-enriched samples because of the line shape distortion caused by the overlapping second-harmonic signal of ¹³C nuclear frequency and other structures at frequencies related to ¹H and ¹³C nuclear Larmor frequencies.