A symmetry-based analysis of Raman and infrared spectra of the compounds (poly(ethylene oxide))3LiCF3SO3 and (poly(ethylene oxide))NaCF3SO3

A symmetry-based factor group analysis is applied to the crystalline compounds (PEO)3LiCF3SO3 and (PEO)NaCF3SO3, focusing on the vibrational modes originating in the intramolecular motion of the triflate anion. The dynamic coupling of the triflate anions in the unit cell yields a vibrational multiplet whose components exhibit different spectral activities. Experimentally, the Raman and IR spectra of the two compounds display multiple bands in the νs(SO3) and δs(CF3) spectral regions. In the δs(CF3) spectral region of each compound, the frequencies of the Raman and IR bands are non-coincident and differ by ∼5 cm−1. The frequency difference indicates a modest amount of dynamical coupling between the triflate anions in the crystal. The spectroscopic analysis of other modes such as δas(CF3), δs(SO3), and δas(SO3) provides useful information about ionic interactions in the crystalline compounds.