BODY FRAMES AND FRAME SINGULARITIES FOR 3-ATOM SYSTEMS

The subject of body frames and their singularities for three-particle systems is important not only for large-amplitude rovibrational coupli ng in molecular spectroscopy, but also for reactive scattering calcula tions. This paper presents a geometrical analysis of the meaning of bo dy frame conventions and their singularities in three-particle systems . Special attention is devoted to the principal axis frame, a certain version of the Eckart frame, and the topological inevitability of fram e singularities. The emphasis is on a geometrical picture, which is in tended as a preliminary study for the more difficult case of four-part icle systems, where one must work in higher-dimensional spaces. The an alysis makes extensive use of kinematic rotations. [S1050-2947(98)0681 1-5].