Lifetime of excited atomic states

Lyαescape during cosmological hydrogen recombination: the 3d-1s and 3s-1s two-photon processes

“…However, the calculation of Cresser et al (1986) was incomplete, since in their attempt to separate the "1 + 1" photon contributions to the two-photon formula 2 from the "pure" twophoton decay terms, without clear justification they neglected the first non-resonant term . Physically, it seems very difficult to separate the "pure" two-photon decay rate from the "1 + 1" resonant contributions (see discussions in Hirata 2008;Karshenboim & Ivanov 2008;Labzowsky et al 2009;Jentschura 2009), e.g., because of non-classical interference effects.…”

“…Using rate coefficients for the vacuum two-photon decays of the 3s and 3d-levels in hydrogen, as computed by Cresser et al (1986), Wong & Scott (2007) concluded that Dubrovich & Grachev (2005) overestimated the impact of two-photon transitions on the ionization history by about one order of magnitude. However, the calculation of Cresser et al (1986) was incomplete, since in their attempt to separate the "1 + 1" photon contributions to the two-photon formula 2 from the "pure" twophoton decay terms, without clear justification they neglected the first non-resonant term .…”

Theory of the multiphoton cascade transitions with two photon links: comparison of quantum electrodynamical and quantum mechanical approaches

“…In the QED approach [31], [32] based on the Low derivation of the Lorentz profile from QED [33], the regularization is performed via the introduction of the sum of two widths, for the initial and intermediate states. Note, that in [13] the possibility of using the sum of the widths was briefly mentioned. In [34]- [36] the QED approach for the description of the multiphoton transitions with cascades was applied to the decays of 3s, 3p, 3d and 4s states in the hydrogen atom.…”

“…This regularization is performed by the introduction of the level widths in the energy denominators which otherwise turn to zero for the photon frequencies, corresponding to the cascade resonances. In the QM phenomenological approach only the width of the intermediate state is usually employed for regularization [12], [13], [27]. We call this approach phenomenological since the width is introduced as an phenomenological parameter.…”

“…Quantum Electrodynamical (QED) corrections to the two-photon decay of H-like ions were studied in [9], [10]. The calculations of different two-photon transition rates in hydrogen atom and H-like ions were given in [11]- [13] in the nonrelativistic approximation and in a fully relativistic approach in [14]- [18].…”