RESONANT FEATURES IN THE ENERGY-DEPENDENCE OF THE RATE OF KETENE ISOMERIZATION

Calculations of the microcanonical isomerization rates for vibrationally excited ketene are presented. The calculations utilize the quantum reactive scattering methodology of absorbing boundary conditions with a discrete variable representation to obtain the cumulative reaction probability for one form of ketene to isomerize via the oxirene intermediate, and were carried out with model 1-, 2-, and 3-degree-of-freedom potential energy surfaces constructed using ab initio data. Significant differences are seen in the energy dependent features of the microcanonical rate for the single mode and multi-mode potentials; e.g., the single mode potential exhibits tunneling resonances with widths of around 1 cm(-1), while the calculations involving more than one degree of freedom have additional resonant features that have widths around 10 cm(-1) and also exhibit non-Breit-Wigner resonant line shapes. This suggests that many of the resonance features are best described as Feshbach (energy transfer, or dynamical) resonances that result because of a strongly bent region on the multi-mode potential energy surfaces. The calculated rates show reasonable qualitative agreement with the experimental results of Lovejoy and Moore [J. Chem, Phys. 98, 7846 (1993)]. (C) 1995 American Institute of Physics