ULTRAVIOLET TRANSITION-PROBABILITIES IN N-II

Oscillator strengths have been calculated for the ultraviolet transition array 2p2-2p3s in the N II spectrum. Recent astrophysical, experimental, and theoretical works have called attention to two interesting features of these lines. First, the intercombination line at 748 angstrom is exceptionally strong; second, the branching ratio between the 1D and 1S decay modes of the 1P-degrees level is unusually large. Both these effects reflect the strong interaction of 2s(2)2p3s with the ''plunging'' configuration 2s2p3; unlike other ions in the carbon isoelectronic sequence, these configurations are overlapping for N II. In the present work multiconfiguration Hartree-Fock (MCHF) wave functions have been used to compute oscillator strengths for all the lines in the 2p2-2p3s transition array. The MCHF results give wavelengths which are within 1% of the observed wavelengths; the length and velocity forms of the oscillator strengths agree with each other to within 7%; and the predicted mean lifetime of the 2p3s 1P-degrees level agrees with a recent beam-foil-laser result to 4% [Y. Baudinet-Robinet et al., Phys. Rev. A 42, 1080 (1990)].