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Scaling laws for the photo-ionisation cross section of two-electron atoms

Chang Woo Byun·Nark Nyul Choi·Min-Ho Lee·Gregor Tanner
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Abstract

The cross sections for single-electron photo-ionisation in two-electron atoms show fluctuations which decrease in amplitude when approaching the double-ionisation threshold. Based on semiclassical closed orbit theory, we show that the algebraic decay of the fluctuations can be characterised in terms of a threshold law $σ\propto |E|^μ$ as $E \to 0_-$ with exponent $μ$ obtained as a combination of stability exponents of the triple-collision singularity. It differs from Wannier's exponent dominating double ionisation processes. The details of the fluctuations are linked to a set of infinitely unstable classical orbits starting and ending in the non-regularisable triple collision. The findings are compared with quantum calculations for a model system, namely collinear helium.

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Chang Woo Byun, Nark Nyul Choi, Min-Ho Lee, Gregor Tanner. 2007-01-08. Scaling laws for the photo-ionisation cross section of two-electron atoms. https://doi.org/10.1103/physrevlett.98.113001

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