THE TRANSFORMATION BETWEEN INTERNAL DISPLACEMENT COORDINATES AND NORMAL COORDINATES OF POLYATOMIC MOLECULES

Abstract

Potential energy surfaces in normal coordinates, derived from the transformation of each grid point of the ab initio internal coordinate surfaces, and those regenerated in small increments using the force constants obtained from fitting the same surface in internal displacement coordinates are compared. The effect of the propagation of the standard deviations in force constants in internal coordinate expansions to the normal coordinate surface and, subsequently, the spectroscopic constants, frequencies, and transition intensities of polyatomic molecules is analyzed. Deviations are obtained using a Monte Carlo method under a Gaussian probability distribution. This procedure results in the most dependable error analysis.