Theoretical study of autoionizing states and lifetimes in multiply excited argon

Autoionization transition rates have been calculated for a representative selection of spectroscopic terms of multiply excited argon atoms. The states selected consist of two highly excited electrons in the Rydberg states (n = 4,5), together with one or two vacancies in the valence shell (n = 3) and a single vacancy in the inner shell (n = 2). Configuration mixing was found to be important. The eigenvalues and eigenstates were found by the truncated diagonalization method (i.e., QHQ is diagonalized). The effect of term splitting was included by calculating the contributions of the quadrupole terms in the interelectron repulsive potentials. The applicability of the msnp +- classification scheme suggested by Cooper, Fano, and Prats for helium was investigated for the outer electrons. Among the doubly excited outer-shell states found here are pairs of states which predominantly have the characteristics of 45sp + and 45sp - levels. However, states of the less-ionized system show less +- character because the shielding of the nucleus by the core electrons removes the degeneracy in energy of 4s5p and 5s4p levels, so there is less mixing when there is more shielding. The lifetimes of the valence-electron (n = 3) shell decay range from approximately 10-17 to approximately 10-13 sec. The lifetimes of the highly excited electrons separate into two widely disparate ranges: from approximately 10-17 to approximately 10-16 sec and from approximately 10-13 to approximately 10-11 sec. The outer-shell states that have lifetimes shorter than the inner shell are those from which it is energetically possible for an electron to fall to a 4s, 4p, or 3d subshell, while the longer lifetimes are for states which can decay only to the n = 3 core