Non-sequential effects in the decay of resonant states

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Abstract
Fano and Prats' treatment of continuum-continuum interaction is used to study the time-dependent behaviour of a system initially in a discrete state coupled to a continuum which is itself coupled to another continuum. This level scheme represents a limiting case in a model which is currently used in the theory of molecular processes, the opposite limit being the sequential scheme which leads to chain-like rate equations. A very different behaviour is obtained in the two limits. In contrast with the results of the sequential model the continuum-continuum coupling produces a change (a decrease) in the decay rate of the discrete state. The two continua are populated in parallel. The calculations provide an explicit example of the influence of higher order terms on a rate constant, a problem which has received attention recently in relation to the evaluation of non-radiative transition rates using approximate molecular wave functions.