Naslov
A view from ab initio AFT approach on model calculations of He double 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 2003 / Anton, Josef ; Cederquist, Henrik ; Larsson, Mats ; Lindroth, Eva ; Mannervik, Sven ; Schmidt, Henning ; Schuch, Reinhold - Stockholm, 2003, 26-26

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
Accurate treatment of double ionization of He requires extensive numerical treatments which, however, do not reveal in a transparent way the double ionization mechanisms. Understanding of double ionization mechanisms in simple terms allows treatment of systems which are more complex than He, and for which ab initio treatments may not be feasible. With such an idea, model calculations have been proposed. However, the mechanisms introduced in these models have not been fully justified. We discuss these models from the point of view of generalized asymptotic Fourier transform (AFT) theory, and we are able to discuss critically, at energies omega > 0.3 keV, assumptions made in building these models. We identify terms neglected by and we find that in situations considered in these terms are relatively small. Our findings provide further insight for possible generalization of the model. We also identify the terms neglected in the model ; we find them very large and we argue that this model is incorrect. The model considers double ionization in terms of an incoherent sum of the shake-off (SO) and knock-out (KO) mechanisms. The KO mechanism, which accounts for all final state interaction in this model, is considered classically. The SO mechanism, which accounts for initial state interaction, taking only the s-state waves of individual electrons in the initial state. It is found that both mechanisms are important at energies from a few hundred eV up to a few keV, while only SO is important at higher energies. In their model the electron which absorbs the photon emerges from the nucleus regardless of energy. They obtain good agreement with experiment and with ab initio numerical approaches from threshold to high energies. The model considers double ionization, at energies above few hundred eV, only in terms of the SO mechanism but taking s, p and d waves in the initial state. They find qualitative agreement with other predictions and with experiment. Using the AFT approach we obtain analytically double and single ionization total cross sections at photon energies omega > 0.3 keV. We are able to identify all the initial and final state correlation effects contributing to the m alpha^2/omega relative correction to the shake results for the cross sections.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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