Rotational-level-dependent radiative lifetimes and branching ratios in NO(B 2Π) (v=7, Ω=1/2,3/2)

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Abstract
The previous study [G. E. Gadd and T. G. Slanger, J. Chem. Phys. 9 2, 2194 (1990)] of the v=0–6 levels of the NO(B 2Π) valence state has been extended to the v=7 level, which is of particular interest because it lies at the first dissociation limit of the molecule, and also in a region where strong homogeneous mixing with the C 2Π Rydberg state manifests itself. Thus, the v=7 radiative lifetime can be affected by both these interactions, which are dependent on rotational level. It has often been argued that the B 2Π3/2 spin–orbit component interacts strongly with C 2Π1/2,3/2, whereas the B 2Π1/2 component is unperturbed. We show here that ‘‘unperturbed’’ is a relative term and that a sensitive way to demonstrate that even the B 2Π1/2 levels are mixed with the C 2Π state is to measure the intensity branching in the B–X 7–v‘ vibrational progression from fluorescent spectra, for different rotational levels. In the present study, excitation of these levels is carried out on the B–X 7–0 band at 191–192 nm. We have investigated the lifetimes of both spin–orbit components of B 2Π(v=7) and find that the decreasing interaction with the C 2Π state with increasing rotational level, in spite of the increasing energy above the dissociation limit, leads to a steady increase in radiative lifetime. The value reached at high J is 350–400 ns, whereas the lifetimes of the Ω=1/2 levels that lie below the dissociation limit approach a value of 600–700 ns, consistent with the extrapolation of lifetime data for v=0–6.