Zusammenfassung
The dynamics of room-temp. ionic liqs. (RTILs) were studied by investigating their dielec. relaxation (DR) and time-resolved optical Kerr-effect (OKE) spectra in the frequency range of ~ 10 MHz to ~ 20 THz. For the studied RTILs the OKE and DR spectra are dominated by a relaxation in the GHz region and extend to a relatively sharp band at around 10 THz. While the first feature is mainly ...
Zusammenfassung
The dynamics of room-temp. ionic liqs. (RTILs) were studied by investigating their dielec. relaxation (DR) and time-resolved optical Kerr-effect (OKE) spectra in the frequency range of ~ 10 MHz to ~ 20 THz. For the studied RTILs the OKE and DR spectra are dominated by a relaxation in the GHz region and extend to a relatively sharp band at around 10 THz. While the first feature is mainly assocd. with the structural relaxation of the fluid through ion rotation (α relaxation), the second indicates the short-time limit of intermol. dynamics. The rather featureless intermediate region is mainly assocd. with intermol. vibrations that are strongly coupled to hindered rotations. In contrast to other RTILs, imidazolium salts show an addnl. sub-α relaxation which dominates the OKE signal and is indicative of the breathing motion of rather long-lived cages.Mixed with polar solvents RTILs were found to retain their ionic liq.-like character up to relatively high levels of diln., but with the overall dynamics considerably speeded up. Below RTIL mole fractions of ~ 0.2-0.4 these systems behave like conventional electrolyte solns. with more or less pronounced ion pairing.
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