Molecular beam study of gateway-coupling N2(C3Πu/a′1Σu-) and chemical quenching of the metastable N2(a′) state

Collisions of metastable N-2 molecules in a beam with a variety of gases result in nitrogen "second positive" emission from a single, isolated level N-2 (C (3) Pi(u1), upsilon = 0, J = 14). The highly selective collisional excitation was explained by a gateway-type coupling with the accidentally nearly degenerate level N-2 (a' (1) Sigma(u)(-), upsilon = 16, J = 14). This identifies even the Lambda component of the emitting level, namely "f". Some additional, minor gateway emissions could in part be related to known N-2(C) perturbations. Unlike gateway emissions reported earlier from this laboratory, the nature of the collision partner was important here. He, Ne, Ar, Kr, N-2, CO, and CO2, all gave about equally strong emission, while almost none was observed with NH3, O-2, and Xe. This is ascribed to the collisional quenching of N-2(a') by Penning ionization (for NH3) or by a harpooning mechanism (for Xe and O-2). (C) 1998 American Institute of Physics.