************OWARI COMPLEX SEMINAR LVIII***********

Title : Including roaming trajectories within the 
TST fold

Speaker : Dr. Rigoberto Hernandez

Affiliation : Center for Computational and 
Molecular Science and Technology, School of 
Chemistry and Biochemistry, 
Georgia Institute of Technology, USA

Date : Tues. Dec. 10th, 13:30 pm (Almost one hour)

Place : 144 Seminar Room (4F), Bulding 1, 
Graduate School of Engineering

Abstract :
The rates of chemical reactions (or any activated 
process) are by definition determined by the flux 
of reactants (or initial states) that end up as 
products (or final states). Through the last hundred 
years of studies on reaction rate theory, it has 
become clear that this can be equated to the flux 
through any surface that divides reactants from 
products as long as only those trajectories that 
end up as products are included in the flux. 
Transition state theory (TST) ignores this last 
clause. It thereby overestimates the rate if any 
of the trajectories recross the dividing surface. 
However, its advantage is that it replaces a 
dynamical calculation with a geometric one. The 
recent identification of roaming trajectories, 
that persist for a long time as neither reactant 
or product without ever visiting near the col on 
the energy landscape, challenges the dogma that 
TST's only error lies in the omission of recrossing 
trajectories. We have investigated these dynamical 
and geometric structures in the case of the ketene 
isomerization. We have constructed roaming 
trajectories that do indeed cause violations of 
the TST hypotheses when the choice of dividing 
surface lies within the phase space that is neither 
associated with reactant or product. However, 
appropriate choices of the dividing surface can 
incorporate the flux of the roaming trajectories 
without suffering recrossings. In this way, the 
existence of roaming trajectories are seen to 
impose a limitation on which dividing surfaces are 
appropriate for the calculation of either exact or 
approximate TST rates, but they do not unseat the 
existence of dividing surfaces that can safely be 
used to calculate rates.

**************************************************