Vanishing fluctuations in atomic spectra

Spectral fluctuations are discussed in the context of the K-matrix theory of interacting autoionizing resonances. New measurements of the doubly-excited spectrum of Ba I in the vicinity of the 6p 1/2 threshold provide unambiguous evidence for the disappearance of fluctuations at a specific excitation energy well below the associated series limit. The authors discuss the origin of this effect, and show that it occurs close to the resonance energy of one broad intruder level, and also suggest a more general connection between the vanishing width effect and the disappearance of fluctuations in atomic spectra.