Ab initio multi-configuration Dirac-Fock calculation of M1 visible transitions among the ground state multiplets of the W26+ ion

The development of fusion reactors has generated a demand for improved knowledge of the atomic properties of tungsten. Using a multi-configuration Dirac-Fock (MCDF) method with a restricted active space treatment, the wavelengths and transition probabilities of the M1 and E2 transitions in the visible light region are calculated for the ground state multiplets of W26+ ions. The theoretical wavelength (388.43 nm) for the H-3(5)-> H-3(4) magnetic dipole transition agrees quite well with the experimental value (389.41 nm). Other transitions theoretically predicted at longer wavelengths are also in good agreement with new experimental observations. The results also indicate that the core-core correlation contributions from the 4d shell are essential to determine the transition properties accurately.