GAS-PHASE LIF STUDY OF THE B(1)SIGMA(--]X-3-SIGMA(-)(X(1)0(+),X(2)1) TRANSITION OF NI()(B0(+))[)

First gas phase spectra of the nitrogen monoiodide radical NI are repo rted. The b(1)Sigma(+)(b0(+)) <-> X(3)Sigma(-)(X(1)0(+), X(2)1) transi tion of NI has been studied by laser-induced fluorescence measurements . Ground state NI radicals were generated in a fast-flow system by rea ction of microwave-discharged nitrogen with iodine vapor. Vibrational levels upsilon = 0, 1, and 2 of the b(1)Sigma(+) state were excited wi th a pulsed dye laser. Rotational and vibrational constants of the X(3 )Sigma(-) and b(1)Sigma(+) states were deduced from analysis of high-r esolution excitation spectra. Time-resolved measurements of the fluore scence decay and measurements of relative line and band intensities al lowed determination of the radiative lifetime of the b state, of band transition probabilities, and of the ratio of transition moments of mu (0)/mu(1) for the b0(+) --> X(1)0(+) and b0(+) --> X(2)1 subtransition s. Comparison of calculated and experimental line intensities and FC f actors shows that treatment of the X(3)Sigma(-) state in terms of a Hu nd's case (a) formalism is preferable to use of a case (c) formalism. (C) 1998 Academic Press.