ON THE ROTATIONAL-CONSTANTS OF FLOPPY MOLECULES

Methods for calculating the rotational constants of floppy triatomic m olecules and atom-linear molecule complexes are discussed. It is shown that previously published equations relating the rotational constants to expectation values of moments of inertia correspond to an approxim ate separation of rotation and vibration. Improved equations, which ta ke account of the Eckart conditions, are presented. The results of the old and new methods are compared with rotational constants obtained b y fitting to J-dependent eigenvalues obtained from exact close-couplin g calculations on Ar-CO2. The improved equations are found to give sub stantially more accurate results.