Photochemical activation of carbon dioxide in Mg(+)(CO(2))(H(2)O)(0,1)

We combine multi-reference ab initio calculations with UV–VIS action spectroscopy to study photochemical activation of CO(2) on a singly charged magnesium ion, [MgCO(2)(H(2)O)(0,1)](+), as a model system for the metal/ligand interactions relevant in CO(2) photochemistry. For the non-hydrated species, two separated Mg(+) 3s–3p bands are observed within 5.0 eV. The low-energy band splits upon hydration with one water molecule. [Mg(CO(2))](+) decomposes highly state-selectively, predominantly via multiphoton processes. Within the low-energy band, CO(2) is exclusively lost within the excited state manifold. For the high-energy band, an additional pathway becomes accessible: the CO(2) ligand is activated via a charge transfer, with photochemistry taking place on the CO(2)(–) moiety eventually leading to a loss of CO after absorption of a second photon. Upon hydration, already excitation into the first and second excited state leads to CO(2) activation in the excited state minimum; however, CO(2) predominantly evaporates upon fluorescence or absorption of another photon. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00214-020-02640-w) contains supplementary material, which is available to authorized users.