I need to include tunneling effect for a rate constant of proton transfer reaction using Wigner expression as it should be since proton is quantum mechanical system. The calculated values at 3 different level theories are 4.413, 4.542 and 4.657. Are theses values acceptable? What does large tunneling correction imply?
Dear Teshome Abute Lelisho,
To my knowledge there is no such range.
The following review article discusses proton transfer reactions which might shed light on the answer to your question:
Biochimica et Biophysica Acta (BBA) - Bioenergetics
Volume 1458, Issue 1, 12 May 2000, Pages 6–27
Review
The mechanism of the proton transfer: an outline
Lev I. Krishtalik
doi:10.1016/S0005-2728(00)00057-8
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Under an Elsevier user license
Abstract
A brief summary of the principal notions of the quantum–mechanical theory of the charge transfer reactions has been presented. In the framework of this theory, the mechanism of the proton transfer consists in the classical medium reorganization that equalizes the proton energy levels in the initial and final states, and a consequent proton transfer via a quantum–mechanical underbarrier transition. On the basis of this mechanism, factors influencing the proton transfer probability, and hence kinetic isotope effect, have been discussed; among them are the optimum tunneling distance, the involvement of the excited vibrational states, etc. Semi-classical and quantum–mechanical treatments of the Swain–Schaad relations have been compared. Some applications to enzymatic proton-transfer reactions have been described.
http://www.sciencedirect.com/science/article/pii/S0005272800000578
You may also check the following link which contains an article entitled " A Method of Calculating Tunneling Corrections For Eckart Potential Barriers" published in JOURNAL OF RESEARCH of the National Bureau of Standards Vol. 86, No.4, July-August 1981
http://nvlpubs.nist.gov/nistpubs/jres/086/jresv86n4p357_A1b.pdf
Hoping this will be helpful,
Rafik
Dear Rafik Karaman,
Thanks a lot for your quick response and valuable information.
See Table 1 of Ref. [3] cited in the NBS paper that Karaman provided. Your tunneling corrections appear to be well within the range of numbers tabulated.
These three numbers look reasonable at around room temperature, and they might be considered to be equivalent, ca. 4-5 (in term of an certainty/accuracy).
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