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 collision al intramolecular energy transfer from the metastable a (4) Pi state w as 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 sp ecific 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 di rect spin-orbit interaction of the emitting B state level with a well- specified level of NO(a). The other two perturbations are caused by in teractions of the respective NO(8) levels with uniquely identifiable l evels of the short-lived NO(b(4) Sigma(-)) state, which in turn are co llisionally 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 iso topic study of the (NO)-N-15-O-16 afterglow, which showed an enhanced population of the vibrational levels B, v = 2 and 3 [14].