Potential energy surfaces determination from high resolution

This paper addresses the question of what it means to have a spectroscopic quality potential energy surface. The literature of the last few years contains numerous references to spectroscopic quality ab initio molecular potentials, yet the definition of spectroscopic quality necessarily depends on the resolution of the experimental spectrum and the theoretical calculation. The accuracy of a molecular potential is perhaps better characterized by asking how well it reproduces experimental observables. This topic is explored by comparing the 1( 113/2) and X2 Yl rd potentials of the halogen monoxides determined from high-resolution spectroscopic studies with potentials computed using ab initio methods. The RKR potentials determined from spectroscopic data provide... 

The observed vibration frequencies of a molecule depend on two features of the molecular structure the masses and equilibrium geometry of the molecule and the potential eneigy surface, or force field, governing displacements from equilibrium. These are described as kinetic and potential effects, respectively for a polyatomic molecule the form and the frequency of each of the 3N—6 normal vibrations depend on the two effects in a complicated way. The object of a force field calculation is to separate these effects. More specifically, if the kinetic parameters are known and the vibration frequencies are observed spectroscopically, the object is to deduce the potential eneigy surface. A major difficulty in this calculation is that the observed frequencies are often insufficient to determine uniquely the form of the potential energy surface, and it is necessary to use data on the frequency shifts observed in isotopically substituted molecules or data on vibration/rotation interaction constants observed in high resolution spectra in order to obtain a unique solution. 

PROGRESS ON THE DETERMINATION OF INTERMOLECULAR POTENTIAL ENERGY SURFACES FROM HIGH RESOLUTION SPECTROSCOPY... 

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