# Direct observation of the collapse of the delocalized excess electron in water

Savolainen, Janne; Uhlig, Frank; Ahmed, Saima; Hamm, Peter; Jungwirth, Pavel (2014). Direct observation of the collapse of the delocalized excess electron in water. Nature Chemistry, 6(8):697-701.

## Abstract

It is generally assumed that the hydrated electron occupies a quasi-spherical cavity surrounded by only a few ​water molecules in its equilibrated state. However, in the very moment of its generation, before ​water has had time to respond to the extra charge, it is expected to be significantly larger in size. According to a particle-in-a-box picture, the frequency of its absorption spectrum is a sensitive measure of the initial size of the electronic wavefunction. Here, using transient terahertz spectroscopy, we show that the excess electron initially absorbs in the far-infrared at a frequency for which accompanying ab initio molecular dynamics simulations estimate an initial delocalization length of ≈40 Å. The electron subsequently shrinks due to solvation and thereby leaves the terahertz observation window very quickly, within ≈200 fs.

## Abstract

It is generally assumed that the hydrated electron occupies a quasi-spherical cavity surrounded by only a few ​water molecules in its equilibrated state. However, in the very moment of its generation, before ​water has had time to respond to the extra charge, it is expected to be significantly larger in size. According to a particle-in-a-box picture, the frequency of its absorption spectrum is a sensitive measure of the initial size of the electronic wavefunction. Here, using transient terahertz spectroscopy, we show that the excess electron initially absorbs in the far-infrared at a frequency for which accompanying ab initio molecular dynamics simulations estimate an initial delocalization length of ≈40 Å. The electron subsequently shrinks due to solvation and thereby leaves the terahertz observation window very quickly, within ≈200 fs.

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