Excitation Mechanism for the Nitrogen Pink Afterglow

An excitation mechanism is described which can account for the observed features of the fast, so-called pink afterglow of pure nitrogen. Metastable sextet atoms are assumed to participate in the formation of loosely bound N4 molecules, which can release sufficient energy to produce the necessary delayed excitation. An improved method of isoelectronic extrapolation gives an energy of 17.2 eV for the metastable N 3s′′′ 6S0 state and 18.0 eV for the N 3s′′′ 4S0 state. With the assumption of a simple model of N4, the detailed processes of spectroscopic excitation are predicted through collisions involving single-electron exchanges.