Modeling of Hot Electron Driven Reactions Over Localized Surface Plasmon Resonance-Active Nanoparticles.

Abstract

In this dissertation, we have used a number of different approaches including simple quantum mechanical models, quantum chemical calculations, electron dynamics, and molecular dynamics to explore the underlying phenomena of photon-mediated chemical reactions over nanostructured catalysts exhibiting strong localized surface plasmon resonance. These reactions could occur either from formation of energetic electrons directly on or to the adsorbate molecule, or formation of energetic electrons on the substrate that are subsequently transferred to the adsorbate. The work presented models portions of both mechanisms. The first portion of this work investigated the properties and characteristics of the interaction between surface plasmons and adsorbate states. Our studies suggest that surface plasmons can enhance the promotion of energetic electrons into empty adsorbate states through strong electric fields at the surface. The surface plasmon increases the interaction of a light molecule with the nanostructure, which can transfer energy into empty adsorbate states if the energy is correct.

We also studied the characteristic time scales for relaxation of energetic electrons and formation of a thermalized hot electron gas. These time scales lay the groundwork for modeling the interaction of the hot electron gas with adsorbate molecules through molecular dynamics simulations within the electronic friction model.

We used position-dependent electronic friction in molecular dynamics simulations employing the Langevin equation to show what type of experimental signatures (e.g. kinetic isotope effect) are expected from this type of interaction. We found that the expected experimental signatures for our model molecular oxygen dissociation over Ag were similar to and consistent with the experimental results for the same. These discoveries help illuminate some of the underlying physical processes for photon-driven chemical transformations over nanostructured catalysts and suggest areas for future study in the discovery and design of these catalysts.