Dielectric relaxation and solvation dynamics in a room-temperature ionic liquid: temperature dependence.

Dielectric relaxation, related polarization and conductivity, and solvation dynamics of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMI(+)PF6(-)) are studied via molecular dynamics computer simulations in the temperature range 300 K ≤ T ≤ 500 K. Two main bands of its dielectric loss spectrum show differing temperature behaviors. As T increases, the absorption band in the microwave region shifts to higher frequencies rapidly, whereas the location of the bimodal far-IR band remains nearly unchanged. Their respective intensities tend to decrease and increase. The static dielectric constant of BMI(+)PF6(-) is found to decrease weakly with T. The ultrafast inertial component of solvation dynamics remains largely unchanged, while their dissipative relaxation component becomes faster. Roles played by ion reorientations and translations in governing dynamic and static dielectric properties of the ionic liquid are examined. A brief comparison with available experimental results is also made.