Gas Phase LIF Study of theb1Σ+(b0+) ↔X3Σ−(X10+,X21) Transition of NI

Abstract First gas phase spectra of the nitrogen monoiodide radical NI are reported. The b 1 Σ + ( b 0 + ) ↔ X 3 Σ − ( X 1 0 + , X 2 1) transition of NI has been studied by laser-induced fluorescence measurements. Ground state NI radicals were generated in a fast-flow system by reaction of microwave-discharged nitrogen with iodine vapor. Vibrational levels v = 0, 1, and 2 of the b 1 Σ + state were excited with a pulsed dye laser. Rotational and vibrational constants of the X 3 Σ − and b 1 Σ + states were deduced from analysis of high-resolution excitation spectra. Time-resolved measurements of the fluorescence decay and measurements of relative line and band intensities allowed determination of the radiative lifetime of the b state, of band transition probabilities, and of the ratio of transition moments μ 0 /μ 1 for the b 0 + → X 1 0 + and b 0 + → X 2 1 subtransitions. Comparison of calculated and experimental line intensities and FC factors shows that treatment of the X 3 Σ − state in terms of a Hund's case (a) formalism is preferable to use of a case (c) formalism.