Gateway-type intramolecular collisional transfer in (NO)-N-15 (a (4)Pi, b (4)Sigma(-)->B (2)Pi)

Excitation of (NO)-N-15 molecules into the B (2) Pi state by collisional intramolecular energy transfer from the metastable a (4) Pi state was studied under single-collision conditions. Passing a beam of (NO)-N-15 (a (4) Pi) through a cell filled with argon at a few mTorr, B (2) Pi --> X(2) Pi emission was observed. It originated from only three specific B state levels, namely (2) Pi(1/2), J = 21.5 and (2) Pi(3/2), J = 21.5 in v = 2 and (2) Pi(1/2), J = 10.5 in v = 3. This selectivity is characteristic of a gateway-type process mediated by spectroscopic perturbations. The analysis showed that in the last case there is a direct spin-orbit interaction of the emitting B state level with a well-specified level of NO(a). The other two perturbations are caused by interactions of the respective NO(8) levels with uniquely identifiable levels of the short-lived NO(b(4) Sigma(-)) state, which in turn are collisionally populated from a broad range of NO(a (4) Pi) levels. This latter mechanism is thus a novel type of gateway process. The results explain the anomalous spectral distribution observed in an earlier isotopic study of the (NO)-N-15-O-16 afterglow, which showed an enhanced population of the vibrational levels B, v = 2 and 3 [14]