Abstract. The purpose of this paper is to calculate the two-photon decay rate corresponding to the two-photon transitions nS → 1S and nD → 1S in hydrogen-like ions with a low nuclear charge number Z (for principal quantum numbers n = 2, ..., 8). Numerical results are obtained within a nonrelativistic framework, and the results are found to scale approximately as (Zα)⁶/n³, where α is the fine-structure constant. We also attempt to clarify a number of subtle issues regarding the treatment of the coherent, quasi-simultaneous emission of the two photons as opposed to one-photon cascades. In particular, the gauge invariance of the decay rate is shown explicitly.

PACS numbers: 31.30.J-, 12.20.Ds, 32.80.Wr, 31.15.-p

Print publication: Issue 15 (18 April 2008)
Received 31 December 2007, in final form 18 February 2008
Published 2 April 2008