Journal of Electron Spectroscopy and Related Phenomena 133 (2003) 65–68 The influence of octupole transitions on the XPS intensities M.B. Trzhaskovskaya a , V.I. Nefedov b,∗ , V.G. Yarzhemsky b , R. Szargan c a St. Petersburg Nuclear Physics Institute of Russian Academy of Sciences, 188350 Gatchina, St. Petersburg, Russia b Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky pr. 31, 119991 Moscow, Russia c Wilhelm-Ostwald-Institut fur Physikalische und Theoretische, Chemie der Universitat Leipzig, Linnestr. 2, D-04103 Leipzig, Germany Received 10 March 2003; received in revised form 1 August 2003; accepted 6 August 2003 Abstract The expression is presented for XPS intensity excited by unpolarized excitation with account for octupole transitions. The non-dipole parameters including octupole transition parameters are calculated in relativistic treatment both for polarized and unpolarized excitations for atoms from Li to Ne. The calculations are performed for 1s shell (Mg K and Al K excitation, and for E kin = 5000 eV and E kin = 10,000 eV) and for 2s and 2p shells (E kin = 500 eV and E kin = 1000 eV). The non-negligible contributions (up to 10%) for the XPS intensity are found for 1s shell when kinetic energy is 5000 and 10,000 eV. In other cases the octupole contributions are less then 1%. © 2003 Elsevier B.V. All rights reserved. Keywords: XPS intensity; Non-dipole transitions; Octupole transitions 1. Introduction In this work, we continue the study of non-dipole transitions in XPS [1–5] (see also references in these papers). The main aim of this paper is to inves- tigate the influence of octupole transitions on the XPS intensities. In the dipole approximation, the term E1 (E is the electric type of interaction be- tween electromagnetic radiation and electrons, and L = 1 is the multipolarity) makes the main contri- bution to a differential cross-section of the atomic photoeffect. In this case the only parameter β is used for the description of the angular distribution of photoelectrons. ∗ Corresponding author. Tel.: +7-95-954-1279. E-mail address: vinef@igic.ras.ru (V.I. Nefedov). The dipole description involves the lowest order O (1) in the expansion in terms of kr where k is the pho- ton energy, and r is the radius of the ionized atomic subshell. However, it was shown in a number of papers (see [2], and references therein) that terms of the order O(k 1 r 1 ) arising in the quadrupole approximation may also make an important contribution even for low pho- toelectron kinetic energies just above the photoioniza- tion threshold. For circular polarized and unpolarized photons the photoelectron angular distribution having regard to the terms O (k 1 r 1 ) may be written as [6]: dσ i dΩ = σ i 4π  1 − β 2 P 2 (cos θ) +  γ 2 sin 2 θ + δ  cos θ  (1) Here σ i is the photoionization cross-section for the ith atomic subshell, P 2 (cos θ) is the second order 0368-2048/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2003.08.002