Volume 217, 2019

Electronic spectroscopy and nanocalorimetry of hydrated magnesium ions [Mg(H2O)n]+, n = 20–70: spontaneous formation of a hydrated electron?

Abstract

Hydrated singly charged magnesium ions [Mg(H2O)n]+ are thought to consist of an Mg2+ ion and a hydrated electron for n > 15. This idea is based on mass spectra, which exhibit a transition from [MgOH(H2O)n−1]+ to [Mg(H2O)n]+ around n = 15–22, black-body infrared radiative dissociation, and quantum chemical calculations. Here, we present photodissociation spectra of size-selected [Mg(H2O)n]+ in the range of n = 20–70 measured for photon energies of 1.0–5.0 eV. The spectra exhibit a broad absorption from 1.4 to 3.2 eV, with two local maxima around 1.7–1.8 eV and 2.1–2.5 eV, depending on cluster size. The spectra shift slowly from n = 20 to n = 50, but no significant change is observed for n = 50–70. Quantum chemical modeling of the spectra yields several candidates for the observed absorptions, including five- and six-fold coordinated Mg2+ with a hydrated electron in its immediate vicinity, as well as a solvent-separated Mg2+/e pair. The photochemical behavior resembles that of the hydrated electron, with barrierless interconversion into the ground state following the excitation.

Graphical abstract: Electronic spectroscopy and nanocalorimetry of hydrated magnesium ions [Mg(H2O)n]+, n = 20–70: spontaneous formation of a hydrated electron?

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
23 Nov 2018
Accepted
07 Dec 2018
First published
10 Dec 2018
This article is Open Access
Creative Commons BY license

Faraday Discuss., 2019,217, 584-600

Electronic spectroscopy and nanocalorimetry of hydrated magnesium ions [Mg(H2O)n]+, n = 20–70: spontaneous formation of a hydrated electron?

T. Taxer, M. Ončák, E. Barwa, C. van der Linde and M. K. Beyer, Faraday Discuss., 2019, 217, 584 DOI: 10.1039/C8FD00204E

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