Abstract
The ultrafast part of the solvation dynamics in series of imidazolium ionic liquids (IL) was investigated by femtosecond three-pulse photon echo peak shift (3PEPS) measurement utilizing an organic dye, oxazine 4 (Ox4) as a probe. The time constant, τ_1, for the ultrafast part (≤300 fs) of the 3PEPS decay exhibited a linear dependence on the square root of the anion mass with the lightest chloride anion manifesting the shortest τ_1. The ultrafast part of the solvation for Ox4 is expected to be affected by the inertial motion of IL anions because Ox4 is a cationic dye that attracts negatively charged particles. A better correlation with the effective mass and the size of both ions included was found for the second time constant, τ_2, (≤3.5 ps).
