Hessian-biased force fields from combining theory and experiment

We describe a new approach of combining experimental and theoretical information to develop accurate valence force fields. We combine the Hessian from ab initio calculations with the structural and spectroscopic data from experiment to generate a new Hessian that is used for extracting force fields. Emphasis is placed on obtaining accurate geometries and accurate frequencies. This technique is illustrated by calculations on formaldehyde, formate anion, thioformaldehyde, carbonyl chloride, and carbonyl fluoride.