Electron-impact excitation of Ar²⁺

Department of Physics, Auburn University, Auburn, AL 36849, USA e-mail: munozjm@auburn.edu

Received: 28 January 2009
Accepted: 12 March 2009

Abstract

Context. Emission from Ar III is seen in planetary nebulae, in H II regions, and from laboratory plasmas. The analysis of such spectra requires accurate electron impact excitation data.

Aims. The aim of this work is to improve the electron impact excitation data available for Ar²⁺, for application in studies of planetary nebulae and laboratory plasma spectra. The effects of the new data on diagnostic line ratios are also studied.

Methods. Electron-impact excitation collision strengths have been calculated using the R-Matrix Intermediate-Coupling Frame-Transformation method and the R-Matrix Breit-Pauli method. Excitation cross sections are calculated between all levels of the configurations 3s²3p⁴, 3s3p⁵, 3p⁶, 3p⁵3d, and 3s²3p³nl (3d ≤ nl ≤ 5s). Maxwellian effective collision strengths are generated from the collision strength data.

Results. Good agreement is found in the collision strengths calculated using the two R-Matrix methods. The collision strengths are compared with literature values for transitions within the 3s²3p⁴ configuration. The new data has a small effect on T_e values obtained from the I(λ7135 Å+ λ7751 Å)/ I(λ5192 Å) line ratio, and a larger effect on the N_e values obtained from the I(λ7135 Å)/I(λ9 μm) line ratio. The final effective collision strength data is archived online.