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Density functional and ab initio methods of quantum
chemical analysis
have been used to probe the
vibrational and chemical reaction dynamics of
three diverse systems: the
regeneration reaction sequence of vitamin
E in aqueous solution, the
metal-catalyzed conversion of alkyne to
vinylidene, and the internal rotation of biphenyl acetylene.
In each
case, additional analysis
of these computational results was necessary to
successfully model experimental data. Although the vitamin E
reactions
were relatively
straightforward to parameterize, they required additional
application of a realistic
solvent model, apparently employed for
the first time to model the
system free energy in the vicinity of the
reaction transition state for a biochemical process. The
metal catalysis
study revealed a reaction
surface of surprising complexity, with five
local minimum geometries,
and the observed chemical kinetics appear to
be justified by application
of the fast equilibrium assumption to at
least one region of the surface. The internal rotation
study builds
on our earlier
investigation of that molecule by numerical integration
of the vibrational
Schroedinger equation, now incorporating basis set
extrapolation and a recent
modification to the energy expression to
achieve excellent agreement with existing spectra.
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