Modified transition state theory and negative apparent activation energies of simple metathesis reactions: application to the reaction CH3 + HBr --> CH4 + Br

The Journal of Physical Chemistry. a
Lev N KrasnoperovPaul Marshall

Abstract

A modified transition state theory (MTST) has been developed for gas-phase reactions with "negative barriers". The theory was applied to the reactions CH3 + HBr(DBr) --> CH4(CH3D) + Br (1a, 1b), which exhibit negative temperature dependences. Accurate ab initio calculations performed with coupled cluster theory extrapolated to the complete basis set limit revealed a transition state located at -2.3 kJ mol(-1) relative to the ground state of the reactants (in reaction 1a), as well as a shallow bound complex. The negative temperature dependence, the absolute values of the rate constant, and the isotope substitution effect are reproduced with good accuracy (10%), without any adjustment or fitting parameters. Analytical expressions are presented for MTST including angular momentum conservation, centrifugal barriers and tunneling. This analysis uses information about the possibly loose entrance barrier and the transition state but does not invoke a statistical intermediate complex.

Citations

Mar 9, 2012·The Journal of Physical Chemistry. a·Manuvesh SangwanLev N Krasnoperov
Nov 28, 2009·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Maarten K SabbeGuy B Marin
Jan 25, 2012·The Journal of Physical Chemistry. a·David M GoldenPaul Marshall
Jun 14, 2019·Chemical Society Reviews·Martin StöhrAlexandre Tkatchenko
Jul 24, 2008·The Journal of Physical Chemistry. a·Arkke J EskolaLev N Krasnoperov
Mar 4, 2011·The Journal of Physical Chemistry. a·Lev N KrasnoperovGeorges Le Bras
May 13, 2020·The Journal of Physical Chemistry. a·Xiaokai ZhangLev N Krasnoperov
Feb 8, 2007·The Journal of Physical Chemistry. a·I M AlecuPaul Marshall
Mar 29, 2007·The Journal of Physical Chemistry. a·Yuri Georgievskii, Stephen J Klippenstein

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