Nanosecond Molecular Dynamics and Vibrational Spectra of Li(+) -Chain- Polyethers in Acetonitrile
Technical rept. no. 9, Sep 1987-Jun 1989
UTAH UNIV SALT LAKE CITY DEPT OF CHEMISTRY
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Ultrasonic relaxation spectra in the 1-500 MHz frequency range for Lithium Perchlorate or Lithium Arsenic Hexafluoride 0.03 to approx. 1 M added to open chain polyethers triglyme in molar ratio R1, or added to poly ethylene oxide in molar ratio RPEO -CH2-CH2-0-Li 4, in the solvent acetonitrile at 25C are reported. The spectra were interpreted by the sum of two Debye relaxation processes. The remarkable finding is that the relaxation times are independent of the chain length in going from triglyme at R1 to a polyethylene oxide of 15,000 average molar weight at RPEO 4. The observed processes appear to reflect a localized cation-polyether interaction here dubbed the ether moiety effect. The relaxations are interpreted by an Eigen- Winkler mechanism in which a cation-ether contact is followed by the polyether chain wrapping around the Li ion. Specific effects in the ultrasonic absorption amplitudes differentiating the spectra of triglyme from the polyether spectra are reported. Infrared spectra between 800 and 900cm of the same systems show cation-ether vibrations due to cage effects. The infrared spectral envelopes of both the polyethers alone and the polyether added to Li are deconvoluted by three Gaussian-Lorentzian bands. For triglyme a weak band at 879cm is strongly enhanced in absorbance and shifted to 870cm when Li is present. This band is attributed to wrapping of the polyether glyme around the cation.
- Physical Chemistry
- Polymer Chemistry