Title: Rates of adsorption and desorption: Entropic contributions and errors due to mean-field approximations

Abstract

We have performed exact classical rate calculations to compute adsorption and desorption rate constants with a model representative of a real system. We compute the desorption rate using transition-state theory by taking the dividing-surface far from the surface of the solid. We find that using a mean-field assumption, i.e., applying potential of mean force to transition state theory, could lead to two orders-of-magnitude errors in the rate constant owing to large fluctuations in the desorption barrier. Furthermore, we compute the adsorption rate by including a dynamical factor which reflects the probability of sticking to the solid surface. We find that the sticking probability is highly sensitive to the coverage. Also, we find that the adsorption rate computed from the mean-field assumption is not very different from the exact adsorption rate. We also compute entropic contribution to desorption rates and compare it to that obtained from two limiting models of adsorption—2D ideal gas and 2D ideal lattice gas. We show that at high temperatures (700 K), the entropic contribution to desorption rates computed from the exact calculations is very close to that obtained from the 2D ideal gas model. However, for lower to intermediate temperatures from 200 K to 500 K,more » the entropic contributions cover a wide range which lies in between the two limiting models and could lead to over two-orders-of-magnitude errors in the rate coefficient.« less

Authors:

Agarwal, Vishal  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-8581-4780"

Metiu, Horia ^[2]

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+ Show Author Affiliations

1. Indian Inst. of Technology (IIT), Kanpur (India)
2. Univ. of California, Santa Barbara, CA (United States). Dept. of Chemistry and Biochemistry

Publication Date:

Tue May 14 00:00:00 EDT 2019

Research Org.:

Univ. of California, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1614579

Alternate Identifier(s):

OSTI ID: 1523558

Grant/Contract Number:  

FG03-89ER14048

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 150; Journal Issue: 18; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Chemistry; Physics; Surface and interface chemistry; Adsorption; Activation energies; Transition state theory; Statistical thermodynamics; Diatomic molecule; Entropy; Reaction rate constants