ON THE ROTATIONAL-CONSTANTS OF FLOPPY MOLECULES

Methods for calculating the rotational constants of floppy triatomic molecules 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 approximate separation of rotation and vibration. Improved equations, which take account of the Eckart conditions, are presented. The results of the old and new methods are compared with rotational constants obtained by fitting to J-dependent eigenvalues obtained from exact close-coupling calculations on Ar-CO2. The improved equations are found to give substantially more accurate results.