Role of Excited States in Charge-Carrier-Induced CO Desorption from Single-Atom Alloys: Insights into Charge Transfer from Correlated Wavefunction Calculations

Plasmonic catalysis could help the chemical industry move toward industrial-scale catalysis powered by low-carbon-emission electricity, via light-emitting diodes as an electrical light source for photocatalysis. In understanding nonthermal plasmonic enhancement of chemical reactions, researchers often invoke the transfer of excited “hot carriers” from a plasmonic metal nanostructure to a nearby molecular species, forming a transient ion. Such a mechanism is dependent on having both an accessible transient-ion state of the molecule and the energy of the adsorbed molecule/surface charge-transfer state be within the energy distribution of the hot carriers. Recent works have drawn connections between inelastic electron tunneling in scanning tunneling microscopy (STM) and transient-ion states in plasmonic catalysis. Typical analysis of STM experiments assumes a simple one-electron picture and that measured desorption thresholds would correspond to the potential bias needed to access adsorbate transient-ion states. In this work, we investigate these ideas with CO adsorbed on various single-atom alloys (SAAs) using density functional embedding and embedded correlated wavefunction theories. Using embedded N-electron valence state second-order perturbation theory based on both embedded density matrix renormalization group and embedded state-averaged complete active space self-consistent field reference wavefunctions, we probe the ground and excited states of different SAAs under charge-neutral, electron-injected, and hole-injected conditions. Our work shows that charge injection to excited states is needed to enable CO desorption and that the relevant excited states may not necessarily involve transient-ion states of the CO but rather charge transfer between the dopant and host metals.