Abstract

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Ultrafast Solvated Electron Dynamics in Liquids and Supercritical Fluids

I-35

Ultrafast Solvated Electron Dynamics in Liquids and Supercritical Fluids


P. Vöhringer1,2

1Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstraße 12, 53115 Bonn, Germany

2p.voehringer@uni-bonn.de

The solvated electron is the “mother of all spin centers”. Formally, it constitutes an unpaired negative elementary charge embedded in a condensed-phase matrix where it is self-stabilized by polarizing its surroundings. In the language of solid-state physics, the electron moves together with its polarization cloud as a quasi-particle, the so-called “polaron”. In the context of solvated electrons in liquids, a heavily debated issue is the motif of electron binding. Is the electron trapped in a localized cavity within the liquid or do we have to regard it as a solvated radical anion cluster in which the spin density is diffusely smeared across a larger number of solvent molecules? How does the binding mode affect the physico-chemical properties of the system and is the reactivity of a “cavity electron” different to that of a “radical cluster electron”? To address some of these issues, we have recently studied extensively the ultrafast spectroscopy of solvated electrons in H-bonded solvents like water, alcohols, and ammonia [1-4]. The electrons were generated chemically (e.g. in metal-ammonia solutions) or photolytically via multi-photon ionization of the neat solvent. The solvent was studied over a wide range of thermodynamic conditions ranging from the tightly packed cryogenic liquid all the way over to the supercritical fluid with gas-like densities. In this talk, we will describe some of the progress we have made in understanding the chemical reactivity of solvated electrons with a particular emphasis on the dynamics of geminate recombination following an ultrafast ionization with energies above and below the band gap of the solvent. Such studies will be discussed in terms of Onsager’s seminal theory for the initial recombination of ions in condensed media and in terms of detailed Monte-Carlo simulations to account for the molecular-level mechanisms that bring about an annihilation of the excess charge and spin densities.

References:

[1] J. Lindner, A.-N. Unterreiner, P. Vöhringer, ChemPhysChem 7, 363 (2006); J. Lindner, A.-N. Unterreiner, P. Vöhringer, J. Chem. Phys. 129, 064514 (2008)

[2] S. Kratz, J. Torres-Alacan, J. Urbanek, J. Lindner, P. Vöhringer, Phys. Chem. Chem. Phys. 12, 12169 (2010); J. Torres-Alacan, S. Kratz, P. Vöhringer, Phys. Chem. Chem. Phys. 13, 20806 (2011);

[3] J. Urbanek, A. Dahmen, J. Torres-Alacan, P. Königshoven, J. Lindner, P. Vöhringer, J. Phys. Chem. B, 116, 2223 (2012); J. Urbanek, P. Vöhringer, J. Phys. Chem. B, 118, 265 (2012); J. Urbanek, P. Vöhringer, J. Phys. Chem. B, 117, 8844 (2013)

[4] P. Vöhringer, Annu. Rev. Phys. Chem. 66, 97 (2015)