Excited states of the negative nitrogen ion: Energies and lifetimes

The present state of knowledge about the excited states of the negative nitrogen ion is reviewed, and calculations of energies and lifetimes of the states belonging to the 2p(4) configuration are reported. Systematic MCHF procedures are applied to the study of the electron affinities of the 2p(4) ID and IS states of N- relative to the 2p(3) D-2 neutral nitrogen parent state. Assuming a 1s(2) {2s, 2p}(3) core for both the atom and the negative ion, a non-relaiivisticelectron affinity of 0.871(2) eV is predicted for the 2D term which implies that the D-1 term in N- is located 1.513 eV above the ground state of nitrogen. Similarly, the S-1 term is predicted to be 1.390(1) eV above the D-1 term: The two terms can decay only via magnetic interactions. and Cl calculations give lifetimes equal to 1 x 10(-10) and 7 x 10(-11) s for the D-1 and S-1 terms, respectively. We estimate the lifetimes to be accurate within a factor of five. The importance of the results, in particular of the lifetime values, for C-14 dating is pointed out.