Breakdown of Kinetic Compensation Effect in Physical Desorption

TL;DR

This study uses kinetic Monte Carlo simulations to investigate the physical origins of the kinetic compensation effect and isokinetic relation in desorption processes, revealing they are due to transient variations and regime transitions rather than true compensation.

Contribution

It demonstrates that the kinetic compensation effect and isokinetic relation are caused by transient variations and regime transitions, not by direct correlation between activation energy and preexponential factor.

Findings

Partial compensation results from transient variations in parameters.

Isokinetic relation arises from a transition to a non-interacting regime.

Variations in the prefactor are insufficient to fully offset changes in activation energy.

Abstract

The kinetic compensation effect (KCE), observed in many fields of science, is the systematic variation in the apparent magnitudes of the Arrhenius parameters $E_a$, the energy of activation, and $\nu$, the preexponential factor, as a response to perturbations. If, in a series of closely related activated processes, these parameters exhibit a strong linear correlation, it is expected that an isokinetic relation will occur, then the rates $k$ become the same at a common compensation temperature $T_c$. The reality of these two phenomena continues to be debated as they have not been explicitly demonstrated and their physical origins remain poorly understood. Using kinetic Monte Carlo simulations on a model interface, we explore how site and adsorbate interactions influence the Arrhenius parameters during a typical desorption process. We find that their transient variations result in a net partial compensation, due to the variations in the prefactor not being large enough to completely offset those in $E_a$, both in plots that exhibit a high degree of linearity and in curved non-Arrhenius plots. In addition, the observed isokinetic relation arises due to a transition to a non-interacting regime, and not due to compensation between $E_a$ and $\ln{\nu}$. We expect our results to provide a deeper insight into the microscopic events that originate compensation effects and isokinetic relations in our system, and in other fields where these effects have been reported.