Radiative de-excitation of the 1s22s3 p 3P0 level in beryllium-like ions: A competition between an E2 and a two-electron one-photon E1 transition

I have performed a complete Multi-Configuration Dirac-Fock calculation of the radiative de-excitation of the 1s²2s3p³P₀ level in beryllium-like ions. Initial and final wave functions are fully optimized, and include valence and core polarization correlation (Coulomb and Magnetic). Non-orthogonality between initial and final state spin-orbitals is exactly accounted for. I show that the main mode of de-excitation of the 1s²2s3p³P₀ level at high Z is an E2 transition to the 1s²2s2p³P₂ and that a two-electron one-photon E1 transition to the 1s²2p^{2 3}P₁ plays an important role at low Z. The latter transition appears to be the difference of two large matrix elements which cancel almost exactly and thus has a very complicated Z dependence, which is studied in the present paper. This revised version was published online in August 2006 with corrections to the Cover Date.