Photolysis versus Photothermolysis of N2O on a Semiconductor Surface Revealed by Nonadiabatic Molecular Dynamics

Identifying photolysis and photothermolysis during a photochemical reaction has remained challenging because of the highly non-equilibrium and ultrafast nature of the processes. Using state-of-the-art ab initio adiabatic and nonadiabatic molecular dynamics, we investigate N 2 O photodissociation on the reduced rutile TiO 2 (110) surface and establish its detailed mechanism. The photodecomposition is initiated by electron injection, leading to the formation of a N 2 O – ion-radical, and activation of the N 2 O bending and symmetric stretching vibrations. Photothermolysis governs the N 2 O dissociation when N 2 O – is short-lived. The dissociation is activated by a combination of the anionic excited state evolution and local heating. A thermal fluctuation drives the molecular acceptor level below the TiO 2 band edge, stabilizes the N 2 O – anion radical, and causes dissociation on a 1 ps timescale. As the N 2 O – resonance lifetime increases, photolysis becomes dominant since evolution in the anionic excited state activates the bending and symmetric stretching of N 2 O, inducing the dissociation. The photodecomposition occurs more easily when N 2 O is bonded to TiO 2 through the O rather than N atom. We demonstrate further that a thermal dissociation of N 2 O can be realized by a rational choice of metal dopants, which enhance p – d orbital hybridization, facilitate electron transfer, and break N 2 O spontaneously. By investigating the charge dynamics and lifetime, we provide a fundamental atomistic understanding of the competition and synergy between the photocatalytic and photothermocatalytic dissociation of N 2 O and demonstrate how N 2 O reduction can be controlled by light irradiation, adsorption configuration, and dopants, enabling the design of high-performance transition-metal oxide catalysts.