Abstract
We combine multi-reference ab initio calculations with UV–VIS action spectroscopy to study photochemical activation of CO2 on a singly charged magnesium ion, [MgCO2(H2O)0,1]+, as a model system for the metal/ligand interactions relevant in CO2 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(CO2)]+ decomposes highly state-selectively, predominantly via multiphoton processes. Within the low-energy band, CO2 is exclusively lost within the excited state manifold. For the high-energy band, an additional pathway becomes accessible: the CO2 ligand is activated via a charge transfer, with photochemistry taking place on the CO2– 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 CO2 activation in the excited state minimum; however, CO2 predominantly evaporates upon fluorescence or absorption of another photon.
Highlights
The accurate theoretical description of electronically excited states remains a very difficult but important task for many applications including photocatalysis, [1] light harvesting, [2] photostability, [3, 4] photosensitizers, [5,6,7,8,9] and many more [10]
We investigated copper formate clusters relevant for carbon dioxide activation on copper centers in the ground state as well as electronically excited states [35,36,37]
The resolved vibrational progression in the low-energy band indicates excitation into a bound state while the structureless high-energy band suggests no excited state minimum in the vicinity of the Franck–Condon point in modeling, Franck–Condon simulations shifted by 0.046 eV are used for the low-energy band in (a), the linearized reflection principle otherwise
Summary
The accurate theoretical description of electronically excited states remains a very difficult but important task for many applications including photocatalysis, [1] light harvesting, [2] photostability, [3, 4] photosensitizers, [5,6,7,8,9] and many more [10]. The combination of theory and UV–VIS spectroscopy provides a powerful tool for characterization of complicated processes in ionic metal complexes upon excitation [34]. With this approach, we investigated copper formate clusters relevant for carbon dioxide activation on copper centers in the ground state as well as electronically excited states [35,36,37]. We investigated copper formate clusters relevant for carbon dioxide activation on copper centers in the ground state as well as electronically excited states [35,36,37] Due to their intriguing charge-transfer chemistry in the ground state, hydrated magnesium ions Mg+(H2O)n have. We combine investigation of the excited state PES with photodissociation experiments in the gas phase to analyze the photochemical activation of C O2 on a M g+ core with and without an additional water molecule
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