The complex coordinate method is applied to the predissociation resonances of two-state model system. The stability of the resonance positions and their widths, as well as the affect of using real and complex basis sets are studied.
A. Autoionization and Predissociation ResonancesAutoionization and predissociation resonances are quasibound states that are associated with non-normalizable solution of the time-independent Schrodinger equation. Therefore, the description of resonance states within the framework of Hilbert space is not straightforward. The complex coordinate (or scaling) method [l] has the advantage that it enables us to obtain the resonance positions and lifetimes by using techniques of bound state approximation theory. Up to the present, attention has primarily been drawn to the application of the complex coordinate method to electron scattering processes, i.e., to atomic [2] and molecular [3] autoionization resonances. In this work we investigate the application of the complex coordinate method to predissociation processes.In the framework of the Born-Oppenheimer approximation, the only type of predissociation resonances that can be observed are the shape-type resonances [4]. These resonances result from the existence of a centrifugal barrier, or from the interaction between two potential curves, in which it is assumed that the electronic eigenfunctions of the Born-Oppenheimer Hamiltonian are independent of nuclear position R: N q = C Ci(R)qi(r).
i = lAs presented in Figure 1 for a two-state model ( N = 2 ) , the crossing of the two potentials El and Ez is avoided. The new potential (the dashed lines in Fig. 1) has only shape-type resonance states. In order to obtain the Feshbach resonances that lie above the crossing point of the two curves in Figure 1, one has to go beyond the Born-Oppenheimer approximation. The