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Diffusive dynamics on potential energy surfaces: Nonequilibrium CO binding to heme proteins

Summary: Diffusive dynamics on potential energy surfaces: Nonequilibrium CO
binding to heme proteins
Noam Agmon and Savely Rabinovich
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew University,
Jerusalem 91904, Israel
(Received 20 March 1992; accepted 15 July 1992)
Theory and practice of reaction dynamics on two-dimensional potential energy surfaces is
investigated. Nonequilibrium multidimensional barrier crossing, occurring when the
initial density is located near the ridgeline separating reactants and products, is treated by
solving the time-dependent Smoluchowski equation as a function of diffusion
anisotropy. For a locally separable potential, and slow relaxation in the perpendicular mode,
the problem reduces to a one-dimensional Smoluchowski equation with a sink term. It
may be further approximated as a first-order reaction with a time-dependent rate coefficient.
These approximations are compared with exact two-dimensional propagations on a
potential surface representing CO binding to a heme. The intermediate-time power-law decay
of the survival probability is analyzed with the aid of the above approximations. The
power also shows some kind of critical behavior near the isotropic diffusion limit, where these
approximations are no longer valid. For fast relaxation, a nonmonotonic survival
probability is observed. The long time decay of the survival probability is governed by the
equilibrium rate coefficient. We calculate its anisotropy dependence and compare it


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry