Vibrational temperature of the adlayer in "hot atom" reaction mechanism

TL;DR

This paper investigates the vibrational temperature of adatoms in hot-atom reaction mechanisms using nonequilibrium thermodynamics, revealing its dependence on reaction rate and energetics, and providing a thermodynamic characterization of the adlayer.

Contribution

It introduces a nonequilibrium statistical thermodynamic approach to define and analyze the vibrational temperature of adatoms during reactive processes.

Findings

Vibrational temperature depends logarithmically on reaction rate.

It exhibits nonlinear scaling with adsorption and binding energies.

The model connects reaction kinetics with thermodynamic properties of the adlayer.

Abstract

Hot-atoms reactions mechanisms bring about reaction rates which are several orders of magnitude higher than those expected in the case of ad-atoms which have thermalized with the surface. This paper addresses the issue of a possible thermodynamic characterization of the adlayer under reactive conditions and at the steady state. In turn, this implies to tackle the question of determining the temperature of the ad-atoms. This is done by means of a nonequilibrium statistical thermodynamic approach, by exploiting a suitable definition of the entropy. The interplay between reaction rate, vibrational temperature of the ad-atoms and adsorbed quantities is highlighted. It is shown that the vibrational temperature depends on reaction rate logarithmically and exhibits a non-linear scaling on physical quantities linked to the energetics of the reaction, namely the adsorption energy and the binding energy of the molecule. The present modeling is also discussed in connection with response equations of nonequilibrium thermodynamics.