Generalized harmonic mode scrambling

A scheme is proposed for decomposing a normal mode of a derivative molecule in terms of the normal modes of parent molecules. In the case of light and heavy isotopically labelled molecules it reduces to the harmonic mode scrambling in the usual sense. The scheme is quite general and provides a quantitative description of the normal mode displacements of one group of atoms in terms of those of another group. It is suitable for the normal mode analysis of a molecule calculated by semi-empirical or ab initio programs which perform vibrational analysis in Cartesian coordinates only.