Ultrafast mid-IR detection of the direct precursor to the presolvated electron following electron ejection from ferrocyanide

Excitation of Fe(CN)₆^4- complex in D₂O solution with a 267 nm ultrashort laser pulse results in rapid charge-transfer-to-solvent, and subsequent electron hydration. Mid-IR transient absorption spectroscopy is used to investigate the ejection and earliest steps in electron solvation. A broad, intense absorption signal is observed with instrument-response-limited rise and 170±20 fs single exponential decay at all probe wavelengths studied, stretching from ~3 to 7 μm. No significant solvent isotope dependence in the time-evolution was seen. The spectral and temporal characteristics of the mid-IR signal provide strong evidence that it arises from a step in solvation immediately preceding formation of the presolvated electron.