Molecular beam study of gateway-coupling N2(C 3Πu/a′ 1Σu−) and chemical quenching of the metastable N2(a′) state

Collisions of metastable N2 molecules in a beam with a variety of gases result in nitrogen “second positive” emission from a single, isolated level N2 (C 3Πu1, v=0, J=14). The highly selective collisional excitation was explained by a gateway-type coupling with the accidentally nearly degenerate level N2 (a′ 1Σu−, v=16, J=14). This identifies even the Λ component of the emitting level, namely “f”. Some additional, minor gateway emissions could in part be related to known N2(C) perturbations. Unlike gateway emissions reported earlier from this laboratory, the nature of the collision partner was important here. He, Ne, Ar, Kr, N2, CO, and CO2, all gave about equally strong emission, while almost none was observed with NH3, O2, and Xe. This is ascribed to the collisional quenching of N2(a′) by Penning ionization (for NH3) or by a harpooning mechanism (for Xe and O2).