The transient absorption spectrum in the range 500 nm-1000 nm was measured with ultrafast time resolution on a flowing neat, aliphatic, room-temperature ionic liquid following anion photodetachment. In this region the spectrum was shown to be a combination of absorption from the electron and the hole. Spectrally-resolved electron quenching determined a bimodal shape for the hole spectrum in agreement with recent computational predictions on a smaller aliphatic ionic liquid [Margulis, J. Am. Chem. Soc. 133, 20186 (2011)]10.1021/ja203412v. For time delays beyond 15 ps, spectral evolution qualitatively agrees with recent radiolysis experiments [Wishart, Faraday Discuss. 154, 353 (2012)10.1039/c1fd00065a]. However, the shape of the spectrum is different, reflecting the contrast in ionization energy between the two methods. Previously unobserved reactivity of the electron was found with a time constant of 300 fs. The results demonstrate solvent control of the rate coefficient for reaction between the electron and proton, with a rapid decline in the rate within the first picosecond.
Bibliographical noteFunding Information:
This work was supported by the (U.S.) Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under SISGR Grant No. DE-FG02-2009ER16118. The authors thank Gary Baker for providing the 1-methyl-1-butyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide samples.