Femtosecond laser driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)

TL;DR

This study models femtosecond laser-induced desorption of O₂ molecules from Ag(110) surfaces, highlighting the role of phonon interactions and electron excitations in the process.

Contribution

It introduces a generalized Langevin oscillator model to incorporate energy exchange between molecules and the surface lattice, advancing the simulation of laser-driven surface reactions.

Findings

Phonon effects significantly influence desorption probabilities.

Electronic density affects the enhancement or reduction of desorption.

The model accurately captures the energy exchange dynamics.

Abstract

We simulate the femtosecond laser induced desorption dynamics of a diatomic molecule from a metal surface by including the effect of the electron and phonon excitations created by the laser pulse. Following previous models, the laser induced surface excitation is treated through the two temperature model, while the multidimensional dynamics of the molecule is described by a classical Langevin equation, in which the friction and random forces account for the action of the heated electrons. In this work, we propose the additional use of the generalized Langevin oscillator model to also include the effect of the energy exchange between the molecule and the heated surface lattice in the desorption dynamics. The model is applied to study the laser induced desorption of O$_2$ from the Ag(110) surface, making use of a six-dimensional potential energy surface calculated within density functional theory. Our results reveal the importance of the phonon mediated process and show that, depending on the value of the electronic density in the surroundings of the molecule adsorption site, its inclusion can significantly enhance or reduce the desorption probabilities.