Electron Excitation Collision Strengths for Singly Ionized Nitrogen

Collision strengths for the astrophysically important lines in N ii have been calculated in the close-coupling approximation using the B-spline Breit–Pauli R-matrix method. The multiconfiguration Hartree–Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 58 bound levels of N ii. The 58 target levels belong to the terms of the ground 2s22p2 and singly excited 2s2p3, 2s22p3s, 2s22p3p, 2s22p3d, 2s22p4s, 2s22p4p, and 2s2p23s configurations. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all 1653 fine-structure transitions among the 58 levels at electron temperatures in the range from 500 to 100,000 K. The line strengths, oscillator strengths, and transition probabilities for all E1 transitions are tabulated. The present results are compared with a variety of other close-coupling calculations. There is an overall good agreement with the 23-state calculation by Hudson & Bell in most part, but some significant differences are also noted for some transitions.