J. Phys. B: At. Mol. Opt. Phys. 23 (1990) L491-L494. Printed in the UK LETTER TO THE EDITOR A new feature of the 3p+3d transition in the Mn atom M Ya Amusiat, V K DolmatovS and M M MansurovS ?A F Ioffe Physical-Technical Institute of the USSR Academy of Sciences, 194021 Leningrad, USSR j: S V Starodubtsev Physical-Technical Institute of the Uzbek SSR Academy of Sciences, 700084 Tashkent. USSR Received 11 June 1990 Abstract. T h e 4s(’S/’S) photoionisation branching ratio for the Mn(3p63d54s2, %) atom is studied at photon energies ho =47-90eV. It is discovered that the 3p+3d transition has a dominant effect on the frequency dependence of this ratio, not only in the region of the 3p+ 3d giant resonance (ho = 47-56 eV), but also far above it-up to hw 3 90 eV. Some other interesting features concerning electron correlations in the Mn atom are also found. It seemed that the last experiments (Krause et a1 1984, Schmidt et al 1985, Schmidt 1985, Kobrin et al 1985) as well as theoretical studies (Davis and Feldkamp 1978, Amusia et al 1983, 1988, Garvin et al 1983) dotted the is concerning the 3p+3d transition in the Mn(3p63d54s2, %) atom. It was proved that this transition manifests itself as the 3p + 3d giant autoionisation resonance in the photoionisation spectra of the Mn atom in the photon energy region 47-56 eV. It seemed it went without saying that the effect of the 3p + 3d transition on the photoionisation process rapidly decreased once out of this resonance region. The aim of this letter is to demonstrate that the 3p + 3d transition in the Mn atom is so strong that its dominant effect on the 4s photoionisation process continues up to the photon energy hw b 90 eV. As a consequence, the ~ s ( ~ S / ’ S ) photoionisation branch- ing ratio has nothing to do with its statistical value, or with the Hartree-Fock calculation results, or, finally, with multielectron calculations taking into account transitions other than the 3p + 3d one. Thus, one more remarkable feature of the 3p+ 3d transition in the Mn atom is discovered. Obviously, it is a common feature of other transitions, like 3p + 3d, in various kinds of atoms with half-filled subshells. The calculations were performed in the frame of the ‘spin-polarised’ random phase approximation with exchange (SP RPAE) (Amusia et al 1983). The SP RPAE makes use of the ‘spin-polarised’ Hartree-Fock approximation (SPHF) (Slater 1974) as the zero- order approximation. In these approximations the ground electron configuration of the Mn atom is given as . . . 3p3T3p3J.3d5T4sT4sJ.. Here the arrows mark the electron spin direction. In the SP RPAE framework the ejection of the 4sT electron produces the 44%) final state and that of the 4 4 electron the ~ s ( ~ S ) state, both having different binding energies. In terms of the SP RPAE the 3p + 3d transition is formed by the 3pJ. + 3dL photoexcitation of the 3pJ. electron to the 3dJ. empty subshell. The calculations showed that the 3dT + EfT and 3pS. + 3dJ atomic transitions have the strongest effect on the 4sTJ-epTJ. photoionisation amplitudes of 4sT and 4sJ electrons at the photon energy hw = 50-90 eV. The action of other atomic excitations, 0953-4075/90/170491+04$03.50 @ 1990 IOP Publishing Ltd L49 1