Naslov
Correlation effects beyond shake in He double and single ionization by absorption of a photon

Autori
Surić, Tihomir ; Pratt, R.H.

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts, 23rd International Conference on Photonic Electronic and Atomic Collisions, ICPEAC / Anton, Josef ; Cederquist, Henrik ; Larsson, Mats - Stockholm, 2003, 25-25

Skup
23rd International Conference on Photonic Electronic and Atomic Collisions, ICPEAC 2003

Mjesto i datum
Stockholm, Švedska, 23.07.2003. - 29.07.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
photoabsorption; Fourier transform; correlation

Sažetak
We study double ionization and single ionization of He from its ground state by absorption of a single photon at incident photon energies omega > 0.3 keV, using modified asymptotic Fourier transform (AFT) approach. We use the usual and, for the considered energies, appropriate framework of nonrelativistic QM neglecting retardation. We are able to identify analytically all the initial and final state correlation effects contributing to the m alpha^2/omega relative correction to the shake results for the total cross sections for single ionization with excitation to a shell n, and for double ionization spectrum in the (shake-off) region in which one electron is very slow. By integrating so obtained spectrum we obtain total cross section for double ionization. Relying on the perturbative result of that the part of the spectrum away from the shake region gives corrections of an order higher than m alpha^2/omega we may argue that our results for total double ionization cross section are also accurate within the order m alpha^2/omega. From the point of view of our results, we discuss other approaches, such as: approximate 3C treatments, extensive numerical CC calculations, MBPT--calculations. We are also able to discuss in more detail recent model calculations. For single ionization with excitation to a shell $n$ and for double ionization spectrum in the shake of region we show that, while shake results are dominated by initial state correlations which result in a final s-state slow or bound electron, the relative m alpha^2/omega correction to shake is large when the final state involves non-s-states of the slow (or bound) electron. By comparison with experiment and also with ab initio theoretical predictions we find that relative corrections to the cross sections (for single with excitation and for double ionization spectrum when one electron is very slow) of order higher than m\alpha^2/omega are small for omega > 0.3 keV. However, up to omega = 2-3 keV, the higher order corrections (coming from the part of the spectrum away from the shake region) are large , which is in agreement with perturbative predictions of hinopan. We find that the m alpha^2/omega relative corrections to the cross sections (which we obtain and present in analytical form, applicable to any ground state He-like ion) suffice to describe the energy dependence of the double to single ratio R at energies above 2-3 keV) of R, and therefore also the double ionization cross section. We find, at energies above the peak, that our results agree very good with experiment and with the ab initio calculations which use a variational initial state. Although such initial state wave function does not represent exactly the terms contributing to the m alpha^2/omega relative corrections, we find that they are sufficiently accurate to reproduce total cross sections for single and double ionization. However, as we discuss, a more accurate treatment, such as ours, of these terms may be needed in calculating differential cross sections. We find less agreement with other more approximate approaches, and we discuss contributions to the m alpha^2/omega relative corrections which are not taken, or are inaccurately taken, with these more approximate approaches.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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