Radiative and predissociative rates for NO A(2)Sigma(+)v '=0-5 and D-2 Sigma(+)v '=0-3

Two-photon laser-induced fluorescence of the NO A-X(0-5,0) and D-X(0-3,0) b ands is used to obtain collision-free lifetimes of the A v'=0-5 and D v'=0- 3 levels in a flow cell. The vibrational trend from NO A v'=0 to v'=3 is sm all, with radiative lifetimes between 205 +/- 7 to 184 +/- 8 ns, respective ly, in agreement with recent calculations derived from branching ratio meas urements and ab initio calculations. Rotationally resolved measurements in the NO A (2)Sigma(+) and D (2)Sigma(+) states reveal very different lifetim e behavior for these nearly isoenergetic levels above the NO X (2)Pi state dissociation limit. The rotational lifetimes of A (2)Sigma(+)v'=4,5 and D ( 2)Sigma(+)v'=0 are basically constant with rotation. However, D (2)Sigma(+) v'=1, 2, and 3 have a strong rotational dependence, decreasing nearly three fold between N'=0 and 20. These observations suggest weak coupling with the ground-state continuum to be the most likely predissociation mechanism for the high A (2)Sigma(+) levels, and rotational on heterogeneous (gyroscopic ) predissociation by the C (2)Pi is the dominant mechanism for the D (2)Sig ma(+) state above v(')=0. The collision-free lifetime of E (2)Sigma(+)v'=0 is 40 +/- 3 ns, and that for F (2)Delta v'=0 is 27 +/- 3 ns. (C) 2000 Ameri can Institute of Physics. [S0021- 9606(00)00419-0].