Experimental determination of the Einstein coefficient for the N(2P–4S) transition

We have measured the Einstein coefficient for the forbidden atomic transition, N(2P–4S), at 346.6 nm, by determining absolute photon emission rates at 346.6 nm when known number densities of N(2P) are in the detector field of view. The N(2P) is generated in a discharge-flow reactor and its number density is determined by vacuum ultraviolet resonance absorption at 174 nm. The absolute response of the monochromator is determined from measurements of the O/NO air afterglow. This first experimental determination, (5.4±1.4)×10−3 s−1, agrees well with published theoretical calculations.