Interchain decay of soliton pairs in polyacetylene

Thin (200–500 nm) samples of polyacetylene have been grown on KBr substrates. An argon-ion laser has been used to optically excite the samples at wavelengths of 514 and 488 nm, creating charged soliton-antisoliton pairs, and Fourier-transform infrared spectroscopy (FTIR) has been done to analyze the excited vibrational modes created. In addition to simply identifying the modes created, this technique allows the measurement of soliton decay half-lives by analyzing the spectra as a function of time after the exciting laser is shut off. Such half-lives have been measured for samples of varying trans-isomer content. The time dependence of the decay is consistent with interchain soliton creation and decay which can be described by a second-order decay process. In addition, the half-lives for interchain soliton decay decrease with increasing trans content as expected for such a process.