Lifetime measurements on perturbed levels of NO(B 2Π) and precise term energy of the NO(a 4Π) state

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Abstract
Using a pulsed near‐UV dye laser, the laser‐induced fluorescence (LIF) excitation spectrum of the NO(B 2Π←X 2Π) transition was measured in the (0,9) band on vibrationally hot NO in a molecular beam. Lifetime measurements were made for some of the B,v=0 and v=3 rotational/fine structure levels, including one which was recently shown to exhibit very specific kinetic effects due to a perturbation by the NO(a 4Π) state [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 100, 1805 (1994)]. This perturbation manifested itself in the present work by a significantly longer lifetime of the 2Π3/2(10.5) level relative to other B,0 levels. The same effect was observed for the B,v=3 2Π1/2(17.5) level. The S/O interaction matrix element is estimated to be very small (≂10−2–10−3 cm−1). The perturbed level pairs must therefore be in very close, accidental coincidence. This was used for a precise determination of the term energy of the a 4Π state as T0(a 4Π)=38 266.74±0.03 cm−1.