Effective collision strengths for transitions in singly ionized nitrogen

The R -matrix method has been used to calculate effective collision strengths for the electronimpact excitation of the carbon- like ion N II. The lowest 23 LS target states are included in the expansion of the total wavefunction, consisting of the nine n = 2 states with configurations 2s(2) 2p(2) and 2s2p(3), along with 14 n = 3 states with configuration 2s(2) 2p3l (l = s, p, d). The fine- structure collision strengths have been obtained by transforming to a jj- coupling scheme using Saraph's JAJOM program, and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. Effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities. Results are presented for transitions among the 2s(2) 2p(2) P-3, D-1, S-1 and 2s2p(3) S-5 levels for electron temperatures in the range log T-e(K) = 2.0 - 5.1, appropriate for astrophysical applications.