Hyperfine coupling constants of NCO in ÃΣ by sub-Doppler spectroscopy

Molecular constants including ¹⁴N hyperfine coupling constants of the NCO radical in the òΣ⁺(000) state have been determined precisely by using the microwave-optical double resonance (MODR) and intermodulated fluorescence (IMF) techniques, where the band was pumped by a dye laser. The results are B = 12 056.559(41), D = 0.0045(16), γ = 22.06(17), b = 430.4(12), c = 80.3(28), and eQq = 2.6(36), all in MHz with one standard error in parentheses. It was found that, because the òΣ⁺ state closely approximates a coupling case (b_βS), MODR did not provide any precise value for the Fermi contact term, but this constant was determined accurately by combining the MODR spectrum with the IMF spectrum.