Tunneling corrections potential energy surfaces

Such a method has recently been developed by Miller. et. al. (28). It uses short lengths of classical trajectory, calculated on an upside-down potential energy surface, to obtain a nonlocal correction to the classical (canonical) equilibrium probability density Peq(p, ) at each point then uses this corrected density to evaluate the rate constant via eq. 4. The method appears to handle the anharmonic tunneling in the reactions H+HH and D+HH fairly well (28), and can... 

This variation in the isotope effect, due to variation in the isotope sensitivity of vf, has been called the Westheimer symmetry effect, and it will be one of the central ideas of this paper. However, in connection with proton transfers it has been attacked, for when more realistic potential energy surfaces are used (that is pf > 0), a much greater degree of force constant asymmetry is required to get a much reduced isotope effect9-11. Bell has therefore suggested that much of the observed variation in the isotope effect is due to variation in the tunnel correction, QhIQd-... 

Attempts to calculate theoretical values for the isotope effects and their temperature dependence were made using a linear activated complex model and a Sato potential energy surface. Various tunneling corrections were applied but only the Bell model ° predicts the curvature observed in log (fcio/ ii) versus l/T. Similar theoretical isotope effect predictions were found using a non-linear transition state model. 

Quantum-mechanical and semiclassical corrections to the simple collision theory ( X and at l ) and activated complex theory (Xac andxg ) for the isotopic H2 + H reactions based on the Weston-Mortensen potential energy surface - tunneling correction. 

There are no classical trajectory calculations for SSMK potential energy surface these are necessary for an evaluation of the actual "tunneling correction = v/v. We see, however, that the values of and decrease at increasing temperatures the... 

In this Section we discuss and compare the results obtained using the various theories of Section 3, and a variational transition state theory with a tunnelling correction [9]. The reaction we concentrate on is H+BrH - HBr+H. We emphasize the rate constants, but also discuss reaction cross sections. The potential energy surface we used in the H+BrH computations is of a semiempirical diatomics in molecules type, the form of which (called DIM-3C) is due to Last and Baer [ll]. The surface contains a three-centre integral term that has been parameter-ised [33] by comparing ESA-CSA calculations with an experimental [3] room temperature rate constant for the D+BrH -) DBr+H reaction. The minimum potential energy path is collinear, and there is a strong... 

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