Widths (lifetimes) and energies for metastable levels of atom-diatom complexes

A method for calculating the energies and widths (intrinsic lifetimes) of metastable levels of atom-diatom van der Waals complexes is presented. It is tested on weakly, moderately, and strongly anisotropic model problems in which the metastable state correlates with a rotationally excited diatom, while the open channel corresponds to the diatom being in a lower rotational state. The method is based upon relating the wavefunction expansion coefficients obtained in an 'infinite wall' secular equation calculation for the metastable state, which employs only square-integrable basis functions, to the Fano theory for the mixing of a discrete state with a continuum. Level widths and energies determined in this way satisfactorily reproduce values obtained through direct numerical solution of the appropriate system of coupled equations; moreover, the present approach requires substantially less computational effort. (Auth.)