COLLISIONAL EXCITATION AND RADIATIVE PROPERTIES OF N-II - THE STRONG INTERCOMBINATION ((1)D-(3)P(0)) TRANSITION AT 748-A

We have constructed a collisional radiative model, using a combination of theoretical calculations and experimental measurements, in order to calculate the excitation and emission properties of electron impact on N II. We have also conducted a spectrometric experiment in order to verify theoretical calculations predicting strong configuration interaction effects, and we find that the measured strength of the N II intercombination transition 2s(2)2p2 1D-2s(2)2p(2P)3s 3P0 at 748.37 angstrom is comparable to the electric dipole multiplet 2s(2)2p2 3P-2s(2)2p(2P)3s 3P0 at 671 angstrom. The measured branching ratio for the 1D-3P0 (J = 1) transition is 0.29 +/- 0.15, in agreement with recent theoretical calculations by Fawcett. Beam foil lifetime measurements for the 3s 3P0 state are also in agreement with the theoretical calculations. This is a remarkably strong intercombination transition for such a light element. If enough strong intercombination transitions of this type exist in the carbon isoelectronic sequence, diagnostic data and collisional radiative quantities could be affected with important astrophysical ramifications. We have employed this finding and our model in a preliminary calculation N II radiative cooling and rate coefficients, and we have examined how the N II temperature diagnostic lines might be affected by intercombination cascading. In respect to planetary atmospheres research, we briefly discuss the excitation and radiative properties of N II excited directly by electrons and by electron dissociative ionization excitation of N2.