Calculated Rate Coefficients for the Electron Impact Excitation of Singly Ionized Nitrogen

Abstract

A 23-state R-matrix calculation has been performed to generate finestructure collision strengths for the electron impact excitation of N II. The target states are represented by configuration interaction wavefunctions and consist of the set of configurations having the form 2s22p2, 2s2p3, 2s22p3l (l = s,p,d). The fine structure collision strengths are generated by transforming to a jj-coupling scheme using the JAJOM program of Saraph, and a sufficiently fine energy mesh has been used to properly delineate the resonance structure. The collision strengths are then averaged over, using a Maxwellian distribution of velocities in order to generate the effective collision strengths. In this paper we use our data to calculate the excitation rate coefficients for six LS transitions so that comparison can be made with experimental and theoretical data presented in Frost et al. The transitions involved are those from the ground state to the 2s22p3s 1Po, 2s2p31Do, 2s22p3p 3Se, 2s2p33So, 2s22p3d 3Do and 2s22p3d 3Po levels, and involve 30 fine-structure levels. The theoretical calculation detailed by Frost et al (also a 23 state R-matrix calculation) produces effective collision strengths for transitions between LS levels, and the authors note `good agreement' with an earlier 13-state R-matrix calculation by Stafford et al. The current calculation improves upon the work of Stafford et al and provides much more data, allowing for comparisons to be made with transitions not included by Stafford et al. In general we find that the current calculation is in better agreement with the calculation described in Frost et al than with that of Stafford et al, and that our calculation provides the same `broad trend' of agreement with the Frost et al experimental rates.