Multiple Minima in Photoionization Cross Sections of Excited Atoms

The dipole matrix element for the Cs 9d→εf photoionizing transition is found theoretically to have three zeros, as a function of photoelectron energy. In addition, a zero in the d→p channel also appears. The explanation of the phenomenon in terms of relative phase shifts is given and the generality of these multiminima is discussed. The consequences of these zeros in cross sections and angular distributions are also spelled out.