Relaxation Dynamics upon Ultrashort UV Photo-Excitation of an Iodide Doped Ionic Liquid and of a Pure Lithium Iodide Melt

Abstract

The ultrafast dynamics of photolytically generated solvated electrons were investigated for the first time in a pure lithium iodide (LiI) melt at 480 °C and in an iodide doped room-temperature ionic liquid. A 70 fs UV-pulse was used to generate excess electrons and their subsequent transient response was monitored in the visible and near-infrared spectral regions. In LiI a pulse-duration limited rise of the induced absorption at all probe wavelengths was attributed to the formation of excess electrons. A minor portion of these electrons (∼20%) were subject to geminate recombination with a time constant of 2 ps. Thereafter, the induced absorption remained unaltered for over 100 ps. The ultrafast dynamics in an iodide doped room-temperature ionic liquid contrasts with the ultrafast response of excess electrons in LiI and in pure room temperature ionic liquids. First, the formation of solvated electrons seems to be delayed by up to 2 ps and second, iodine atoms act as efficient electron scavengers on a tens of ps time scale. As a result, ∼80% of the initially prepared solvated electrons undergo geminate recombination after about 70 ps. Furthermore, an additional component around 720 nm is attributed to the formation of diiodide.