Trajectory Calculations over the Potential Energy Hypersurface

Trajectory Calculations over the Potential Energy Hypersurface 

Calculation of an ab initio potential energy hypersurface for has permitted the study thereon of the dynamics of the reaction (H2,HD) This investigation is to be contrasted with most previous trajectory calculations by a number of workers, where ignorance of the actual hypersurface required a plausible form to be assumed for it. This example therefore provides an important test of the ability of trajectory calculations to simulate the dynamics of reactive collision processes. 

The extensive use by Dugan and Magee of trajectory calculations to compute close-collision cross sections for the collision of ions with polar molecules has been reviewed in Section 4.2.2d. For such calculations, a form for only the attractive part of the potential need be assumed and, in this case, a particular value of the ion-molecule separation was used to define a close collision. The form chosen for the potential was the simple, anisotropic, electrostatic ion-dipole potential plus the ion-induced-dipole potential and, for reasons discussed in that section, such a model may only be applied to ion-molecule collisions at thermal energies. 

Such studies are suggestive, but have limited predictive value, since 

In the absence of direct knowledge of the potential energy hypersurface, either from calculation or experiment (e.g., via elastic scattering), some simplified model must be assumed for it. The question then arises as to how simple the model may be and yet simulate the experimental observables of the reaction, namely total and differential cross sections, velocity distributions, etc. It is to such questions that the recent studies of George and Suplinskas are particularly relevant.  

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