The application of exterior complex scaling in calculations on resonances in nuclear motion in molecular systems

The application of the method of exterior complex scaling to find complex resonance energies by direct numerical integration is presented. Details of the numerical procedures required are discussed and results are presented for rotational predissociation resonances in H₂. The advantage of the exterior-scaling approach is that it requires analytic continuation of the potential to complex values of the coordinates only in the asymptotic or near-asymptotic region. Therefore any representation of the potential is adequate, including piecewise-continuous representations such as cubic splines. In contrast, application of the usual complex-scaling (rotated coordinates) procedure generally requires that the potential be represented by a single analytic function.