Radiative rates of singlet–triplet transitions in nitrogen halide diatomics

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Abstract
Near infrared emissions from the a 1Δ→X 3Σ− transitions in NCl and NBr are observed following pulsed laser photolysis of gaseous ClN3 and BrN3, respectively. From the time decay of the NCl emission, the radiative rate of the a→X transition is found to be (4.87±0.37)×102 s−1. Rate constants for collisional quenching of NCl(a 1Δ) by ClN3 and N2 are determined to be (1.27±0.13)×10−13 and 5×10−16 cm3 s−1, respectively. From the NBr emission, the radiative rate of the a→X transition in this molecule is found to be (1.24±0.34)×103 s−1, and the rate constant for collisional quenching of NBr (a 1Δ) by BrN3 is (1.76±0.04)×10−11 cm3 s−1. The radiative rates of the a 1Δ→X 3Σ− and b 1Σ+→X 3Σ− transitions in NF, NCl, and NBr are discussed in terms of spin-orbit mixing of states of the π4π*2, π3π*3, and π4π*σ* electronic configurations. Approximate spin-orbit matrix elements for the individual interactions are calculated based on one electron integrals. Although the calculations present a reasonable model for the a→X transitions, the results conflict with spectroscopic data for the b→X systems.

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