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Charge-transfer and impulsive electronic-to-vibrational energy conversion in ferricyanide: ultrafast photoelectron and transient infrared studies


Ojeda, José; Arrell, Christopher A; Longetti, Luca; Chergui, Majed; Helbing, Jan (2017). Charge-transfer and impulsive electronic-to-vibrational energy conversion in ferricyanide: ultrafast photoelectron and transient infrared studies. Physical Chemistry Chemical Physics (PCCP), 19(26):17052-17062.

Abstract

The photophysics of ferricyanide in H2O, D2O and ethylene glycol was studied upon excitation of ligand-to-metal charge transfer (LMCT) transitions by combining ultrafast photoelectron spectroscopy (PES) of liquids and transient vibrational spectroscopy. Upon 400 nm excitation in water, the PES results show a prompt reduction of the Fe 3+ to Fe 2+ and a back electron transfer in ∼0.5 ps concomitant with the appearance and decay of a strongly broadened infrared absorption at ∼2065 cm -1 . In ethylene glycol, the same IR absorption band decays in ∼1 ps, implying a strong dependence of the back electron transfer on the solvent. Thereafter, the ground state ferric species is left vibrationally hot with significant excitation of up to two quanta of the CN-stretch modes, which completely decay on a 10 ps time scale. Under 265 nm excitation even higher CN-stretch levels are populated. Finally, from a tiny residual transient IR signal, we deduce that less than 2% of the excited species undergo photoaquation, in line with early flash photolysis experiments. The latter is more significant at 265 nm compared to 400 nm excitation, which suggests photodissociation in this system is an unlikely statistical process related to the large excess of vibrational energy.

Abstract

The photophysics of ferricyanide in H2O, D2O and ethylene glycol was studied upon excitation of ligand-to-metal charge transfer (LMCT) transitions by combining ultrafast photoelectron spectroscopy (PES) of liquids and transient vibrational spectroscopy. Upon 400 nm excitation in water, the PES results show a prompt reduction of the Fe 3+ to Fe 2+ and a back electron transfer in ∼0.5 ps concomitant with the appearance and decay of a strongly broadened infrared absorption at ∼2065 cm -1 . In ethylene glycol, the same IR absorption band decays in ∼1 ps, implying a strong dependence of the back electron transfer on the solvent. Thereafter, the ground state ferric species is left vibrationally hot with significant excitation of up to two quanta of the CN-stretch modes, which completely decay on a 10 ps time scale. Under 265 nm excitation even higher CN-stretch levels are populated. Finally, from a tiny residual transient IR signal, we deduce that less than 2% of the excited species undergo photoaquation, in line with early flash photolysis experiments. The latter is more significant at 265 nm compared to 400 nm excitation, which suggests photodissociation in this system is an unlikely statistical process related to the large excess of vibrational energy.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > General Physics and Astronomy
Physical Sciences > Physical and Theoretical Chemistry
Language:English
Date:1 January 2017
Deposited On:21 Nov 2018 16:11
Last Modified:28 Jul 2020 14:01
Publisher:Royal Society of Chemistry
ISSN:1463-9076
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1039/c7cp03337k

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