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Abstract: The total single-photon ionisation cross section was calculated for heliumatoms in their ground state. Using a full configuration-interaction approachthe photoionisation cross section was extracted from the complex-scaledresolvent. In the energy range from ionisation threshold to 59\,eV our resultsagree with an earlier $B$-spline based calculation in which the continuum isbox discretised within a relative error of $0.01\%$ in the non-resonant part ofthe spectrum. Above the $\He^{++}$ threshold our results agree on the otherhand very well to a recent Floquet calculation. Thus our calculation confirmsthe previously reported deviations from the experimental reference data outsidethe claimed error estimate. In order to extend the calculated spectrum to veryhigh energies, an analytical hydrogenic-type model tail is introduced thatshould become asymptotically exact for infinite photon energies. Itsuniversality is investigated considering also H$^-$, Li$^+$, and HeH$^+$. Withthe aid of the tail corrections to the dipole approximation are estimated.



Autor: Alexander Stark, Alejandro Saenz

Fuente: https://arxiv.org/







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