Forbidden Transitions in One- and Two-Electron Atoms

Publisher Summary The notion of forbidden decays has its roots in the Ritz combination principle and the idea that the measured frequencies of all observed spectral lines can be expressed as the difference of two term frequencies. The fact that for any system not all the possible differences of the known terms are observed initially led to a separation of the possible radiative transitions into allowed and forbidden types. The well-known selection rules for electromagnetic decay, which provide a time-tested basis for this separation, predate quantum mechanics and were originally based on classical electromagnetic theory applied to the vector model of the atom. It is now possible to make a more refined distinction between the allowed and forbidden decays, and this chapter shows what are considered the appropriate selection rules in some detail. The chapter reviews recent theoretical and experimental work on forbidden transitions in the one- and two-electron systems. The chapter also considers the characterization of the forbidden transitions and each of the known transition types.

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