An R-matrix calculation of the electron impact excitation of the fine-structure levels in neon-like selenium (Se XXV)

The authors present calculations based on the R-matrix method for electron impact excitation of Ne-like selenium. In these elaborate calculations, the 27 fine-structure levels arising from the four lowest configurations 2s 2 2p 6 , 2s 2 2p 5 3s, 2s 2 2p 5 3p and 2s 2 2p 5 3d are included. Terms of the Breit-Pauli Hamiltonian are explicitly included in determining both the target and the scattering wavefunction. All target levels included in the calculations are represented by configuration interaction wavefunctions using the 1s, 2s, 2p 3s, 3p and 3d orbitals. The collision strengths are compared with previous theoretical results. For many transitions they found complicated resonance structures in the excitation cross sections. The excitation cross sections are integrated over a Maxwellian distribution of electron energies to give electron excitation rate coefficients; the rates for transitions from the ground state to each fine-structure level are tabulated and are compared with results from distorted-wave calculations. At low temperatures (T c =500 eV) some of their rates are six times larger than earlier calculations. They also present estimates of the relative populations of the (2p 5 3p) 1 D 2 and 1 S 0 levels of Se XXV at T c =1000 eV and at various electron densities.