In this paper we consider the general problem of a discrete state interacting with a continuum which is bounded below in energy. We investigate the optical properties of the new state which splits off below the threshold and determine its energy and oscillator strength in terms of the transition moments of the zerohyphen;order states and the matrix elements of the level shift operator. We study in particular the case of predissociation in diatomic molecules and provide numerical estimates and experimental criteria for the observation of this new effect. Finally, we discuss certain more general situations in which this phenomenon is expected to arise and suggest appropriate extensions of the present, semiempirical, treatment.
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