Variation in cross section fluctuations arising from a Rydberg series interacting with a broad level

The degree of fluctuations in a cross section arising from a Rydberg series varies with energy if the series crosses a broad underlying level. The authors derive the general laws that describe this variation. When only one channel is open, fluctuations vanish at one energy, but this happens only exceptionally if more channels are open. A figure showing photoabsorption cross section of Ba near photon energy of 7.6 eV is given.