Electron impact excitation of Si X

Abstract

Excitation cross sections of Si9+ by electron impact have been computed, for comparison, in different approximations and in different target descriptions using a computer package developed at University College London. Collision strengths have been calculated for fine-structure transitions between the ground configuration term 2s22p 2P0 and the excited configurations 2s2p2 4P, 2D, 2S, 2P and 2p3 4S degrees , 2D degrees , 2P degrees of Si9+ using the eight-state close-coupling approximation and distorted-wave approximation for the energy range 6.0 to 70.0 Ryd. Configuration interaction and spin-orbit interaction within the configurations 2s2p2, 2p3, 2s2p3d, 2p23d, 2s3d2 and 2s23d have been taken into account. Wavefunctions for the target states and hence the oscillator strengths are calculated by using the multiconfiguration Hartree-Fock approximation with the four orbitals 1s, 2s, 2p, 3d and the above mentioned three odd and four even configurations. Collision strengths have also been calculated by a five-state close-coupling approximation between the configurations 2s22P 2P degrees and 2s2p2 4P, 2D, 2S, 2P allowing configuration interaction between 2s2P 2P degrees , and 2p3 2P degrees configuration and spin-orbit interaction within the 2s2p2 configuration. The authors' results indicate that the use of an elaborate target description and a more accurate treatment of the collision problem may change some cross sections by more than 25%. The results are compared with earlier work. This problem has important applications in plasma diagnostics and in the interpretation of the extreme ultraviolet solar emission spectrum.