Photochemical activation of carbon dioxide in Mg+(CO2)(H2O)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 + 3 s –3 p 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.