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Photoionization cross section: Exact expansion over resonances and natural line shape

Gabriel Álvarez, Harris J. Silverstone

The photoionization cross section is analyzed as a sum of resonance contributions plus background. The contribution of each resonance is proportional to the square of a complex transition-dipole matrix element divided by a complex energy denominator and has a natural asymmetric line shape that is the superposition of a dispersive and an absorptive Lorentzian component.

Physical Review AOct 1, 198910 citations

Interaction of laser light with the 21S0metastable state of helium

V. L. Jacobs, Junya Mizuno

The cross sections for singly stimulated two-photon emission and anti-Stokes Raman scattering from the 21S0 metastable state of helium care calculated by a variational procedure for incident photon wavelengths in the range from 5000 AA to 50 mu m.

Journal of Physics B Atomic and Molecular PhysicsJun 1, 19723 citations

The interaction of normal and metastable helium atoms

Richard A. Buckingham, A. Dalgarno

Abstract The energy of interaction of a normal helium atom and one excited to the first triplet or singlet metastable state is calculated over a range of nuclear separations from a0 to 12a0. The Heitler-London method is followed, with inclusion of all non-orthogonality integrals, and using analytic wave functions. Because of identity of the nuclei, g and u states of interaction occur, the energy of the u state having a minimum at about 2·1a0, and a positive maximum of 0·29 and 0·26 eV (for triplet and singlet states respectively) at about 4a0; the g state is entirely repulsive. Comparison is made with experimental evidence for the binding energy of normal and metastable (triplet) atoms. An estimate is made of the second-order dipole-dipole interaction for large separations, and it seems certain that the first-order interaction dominates at least to 12a0. Methods of calculating the necessary integrals are discussed in an appendix.Abstract The energy of interaction of a normal helium atom and one excited to the first triplet or singlet metastable state is calculated over a range of nuclear separations from a0 to 12a0. The Heitler-London method is followed, with inclusion of all non-orthogonality integrals, and using analytic wave functions. Because of identity of the nuclei, g and u states of interaction occur, the energy of the u state having a minimum at about 2·1a0, and a positive maximum of 0·29 and 0·26 eV (for triplet and singlet states respectively) at about 4a0; the g state is entirely repulsive. Comparison is made with experimental evidence for the binding energy of normal and metastable (triplet) atoms. An estimate is made of the second-order dipole-dipole interaction for large separations, and it seems certain that the first-order interaction dominates at least to 12a0. Methods of calculating the necessary integrals are discussed in an appendix.

Proceedings of the Royal Society of London A Mathematical and Physical SciencesJul 8, 195287 citations

Three-photon ionization of metastable helium atoms. [Cross sections, resonance state perturbations]

Joseph S. Bakos, Nikolai B. Delone, Annamária Kiss +2 more

Journal of Experimental and Theoretical PhysicsAug 1, 19760 citations

Nonradiative formation of the positron-helium triplet bound state

Joseph Di Rienzi, Richard J. Drachman

We have previously calculated the cross section for radiative formation of the interesting bound state consisting of a positron bound to helium, where the atomic electrons are in the triplet spin state. That process uses the metastable triplet helium system as target, and, as expected, it has a very small cross section. In this paper we examine a more probable process in which the state of interest is produced in an exchange rearrangement collision between a positronium atom and the singlet helium ground state: $\mathrm{Ps}+\mathrm{He}(^{1}S^{\mathrm{e}})\ensuremath{\rightarrow}\mathrm{Ps}{\mathrm{He}}^{+}(^{3}S^{\mathrm{e}})+{e}^{\ensuremath{-}}$. The present calculation is done in the plane-wave Born approximation, using simple initial and final wave functions and compares post and prior forms.We have previously calculated the cross section for radiative formation of the interesting bound state consisting of a positron bound to helium, where the atomic electrons are in the triplet spin state. That process uses the metastable triplet helium system as target, and, as expected, it has a very small cross section. In this paper we examine a more probable process in which the state of interest is produced in an exchange rearrangement collision between a positronium atom and the singlet helium ground state: $\mathrm{Ps}+\mathrm{He}(^{1}S^{\mathrm{e}})\ensuremath{\rightarrow}\mathrm{Ps}{\mathrm{He}}^{+}(^{3}S^{\mathrm{e}})+{e}^{\ensuremath{-}}$. The present calculation is done in the plane-wave Born approximation, using simple initial and final wave functions and compares post and prior forms.

Physical Review AFeb 20, 20074 citations

Resonance photoionization of the excited helium

S. Danzan, B. Zhadamba, Ts. Sukhbaatar +2 more

Unknown eBooksJan 1, 19930 citations

Calculation of Photoabsorption Processes in Helium

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