A theory of phonon induced friction on molecular adsorbates

TL;DR

This paper develops a comprehensive theory describing how surface phonons influence molecular adsorbates, linking vibrational dynamics to friction and reaction rates, and validating the model with experimental CO desorption data.

Contribution

It introduces a generalized Langevin equation framework to quantify phonon-induced friction and its effect on reaction rates for adsorbates on surfaces.

Findings

Physisorbed species mainly couple to acoustic phonons.

Chemisorbed species primarily couple to local vibrations.

Phonon-adjusted reaction rates align better with experimental data.

Abstract

In this manuscript, we provide a general theory for how surface phonons couple to molecular adsorbates. Our theory maps the extended dynamics of a surface's atomic vibrational motions to a generalized Langevin equation, and by doing so captures these dynamics in a single quantity: the non-Markovian friction. The different frequency components of this friction are the phonon modes of the surface slab weighted by their coupling to the adsorbate degrees of freedom. Using this formalism, we demonstrate that physisorbed species couple primarily to acoustic phonons while chemisorbed species couple to dispersionless local vibrations. We subsequently derive equations for phonon-adjusted reaction rates using transition state theory and demonstrate that these corrections improve agreement with experimental results for CO desorption rates from Pt(111).