TY - JOUR
T1 - Modified transition state theory and negative apparent activation energies of simple metathesis reactions
T2 - Application to the reaction CH 3 + HBr → CH 4 + Br
AU - Krasnoperov, Lev N.
AU - Peng, Jingping
AU - Marshall, Paul
PY - 2006/3/9
Y1 - 2006/3/9
N2 - A modified transition state theory (MTST) has been developed for gas-phase reactions with "negative barriers". The theory was applied to the reactions CH 3 + HBr(DBr) → CH 4(CH 3D) + 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 la), 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.
AB - A modified transition state theory (MTST) has been developed for gas-phase reactions with "negative barriers". The theory was applied to the reactions CH 3 + HBr(DBr) → CH 4(CH 3D) + 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 la), 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.
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U2 - 10.1021/jp054435q
DO - 10.1021/jp054435q
M3 - Article
C2 - 16509633
AN - SCOPUS:33645666197
SN - 1089-5639
VL - 110
SP - 3110
EP - 3120
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 9
ER -