Title: Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

Abstract

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the samplingmore » of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. Finally, this analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes.« less

Authors:

Soudackov, Alexander V.  ^[1];

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Hammes-Schiffer, Sharon ^[1]

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1. Univ. of Illinois at Urbana-Champaign, IL (United States). Dept. of Chemistry

Publication Date:

Tue Nov 17 00:00:00 EST 2015

Research Org.:

Energy Frontier Research Centers (EFRC), Washington D.C. (United States). Center for Molecular Electrocatalysis (CME)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1370963

Alternate Identifier(s):

OSTI ID: 1226187

Grant/Contract Number:  

AC05-76RL01830; Center for Molecular Electrocatalysis

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 143; Journal Issue: 19; Related Information: CME partners with Pacific Northwest National Laboratory (lead); University of Illinois, Urbana-Champaign; Pennsylvania State University; University of Washington; University of Wyoming; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous); catalysis (heterogeneous); solar (fuels); bio-inspired; energy storage (including batteries and capacitors); hydrogen and fuel cells; charge transport; materials and chemistry by design; synthesis (novel materials)