The microwave spectrum of the NCI radical in the electronically excited (a¹Δ) state

The pure rotational spectrum of the ¹⁴N³⁵Cl radical in the first electronically excited a ¹Δ state was detected by microwave spectroscopy. The NCl radical was produced by a de-glow discharge of an N₂ and Cl₂ mixture between 175-210 K. Seven rotational transitions for ν=0 and five for ν=l, showing hyperfine structures due to the nitrogen and chlorine nuclei, were observed in the 162-404 GHz region. The rotational, centrifugal distortion, and hyperfine coupling constants including nuclear spin-rotation coupling constant of the chlorine nucleus were determined accurately by a least-squares analysis of the measured frequencies. The equilibrium structural parameters were derived and discussed.