skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The strange kinetics of the C{sub 2}H{sub 6} + CN reaction explained.

Abstract

In this paper, we employ state of the art quantum chemical and transition state theory methods in making a priori kinetic predictions for the abstraction reaction of CN with ethane. This reaction, which has been studied experimentally over an exceptionally broad range of temperature (25-1140 K), exhibits an unusually strong minimum in the rate constant near 200 K. The present theoretical predictions, which are based on a careful consideration of the two distinct transition state regimes, quantitatively reproduce the measured rate constant over the full range of temperature, with no adjustable parameters. At low temperatures, the rate-determining step for such radical-molecule reactions involves the formation of a weakly bound van der Waals complex. At higher temperatures, the passage over a sub-threshold saddle point on the potential energy surface, related to the formation and dissolution of chemical bonds, becomes the rate-determining step. The calculations illustrate the changing importance of the two transition states with increasing temperature and also clearly demonstrate the need for including accurate treatments of both transition states. The present two transition state model is an extension of that employed in our previous work on the C2H4 + OH. It incorporates direct ab initio evaluations of the potential inmore » classical phase space integral based calculations of the fully coupled anharmonic transition state partition functions for both transition states. Comparisons with more standard rigid-rotor harmonic oscillator representations for the 'inner' transition state illustrate the importance of variational, anharmonic, and nonrigid effects. The effects of tunneling through the 'inner' saddle point and of dynamical correlations between the two transition states are also discussed. A study of the kinetic isotope effect provides a further test for the present two transition state model.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
914898
Report Number(s):
ANL/CHM/JA-58141
Journal ID: ISSN 1089-5639; JPCAFH; TRN: US200817%%2
DOE Contract Number:  
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem. A; Journal Volume: 111; Journal Issue: 19 ; May 17, 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CHEMICAL REACTION KINETICS; ETHANE; CYANIDES; MATHEMATICAL MODELS

Citation Formats

Georgievskii, Y., Klippenstein, S. J., Chemistry, and SNL. The strange kinetics of the C{sub 2}H{sub 6} + CN reaction explained.. United States: N. p., 2007. Web. doi:10.1021/jp068430k.
Georgievskii, Y., Klippenstein, S. J., Chemistry, & SNL. The strange kinetics of the C{sub 2}H{sub 6} + CN reaction explained.. United States. doi:10.1021/jp068430k.
Georgievskii, Y., Klippenstein, S. J., Chemistry, and SNL. Thu . "The strange kinetics of the C{sub 2}H{sub 6} + CN reaction explained.". United States. doi:10.1021/jp068430k.
@article{osti_914898,
title = {The strange kinetics of the C{sub 2}H{sub 6} + CN reaction explained.},
author = {Georgievskii, Y. and Klippenstein, S. J. and Chemistry and SNL},
abstractNote = {In this paper, we employ state of the art quantum chemical and transition state theory methods in making a priori kinetic predictions for the abstraction reaction of CN with ethane. This reaction, which has been studied experimentally over an exceptionally broad range of temperature (25-1140 K), exhibits an unusually strong minimum in the rate constant near 200 K. The present theoretical predictions, which are based on a careful consideration of the two distinct transition state regimes, quantitatively reproduce the measured rate constant over the full range of temperature, with no adjustable parameters. At low temperatures, the rate-determining step for such radical-molecule reactions involves the formation of a weakly bound van der Waals complex. At higher temperatures, the passage over a sub-threshold saddle point on the potential energy surface, related to the formation and dissolution of chemical bonds, becomes the rate-determining step. The calculations illustrate the changing importance of the two transition states with increasing temperature and also clearly demonstrate the need for including accurate treatments of both transition states. The present two transition state model is an extension of that employed in our previous work on the C2H4 + OH. It incorporates direct ab initio evaluations of the potential in classical phase space integral based calculations of the fully coupled anharmonic transition state partition functions for both transition states. Comparisons with more standard rigid-rotor harmonic oscillator representations for the 'inner' transition state illustrate the importance of variational, anharmonic, and nonrigid effects. The effects of tunneling through the 'inner' saddle point and of dynamical correlations between the two transition states are also discussed. A study of the kinetic isotope effect provides a further test for the present two transition state model.},
doi = {10.1021/jp068430k},
journal = {J. Phys. Chem. A},
number = 19 ; May 17, 2007,
volume = 111,
place = {United States},
year = {Thu May 17 00:00:00 EDT 2007},
month = {Thu May 17 00:00:00 EDT 2007}
}