Microwave spectrum of NCl in the second electronically excited state (b ¹∑⁺)

The pure rotational transitions of N³⁵Cl in the second electronically excited state, b ¹∑⁺, were detected together with those of the isotopic species N³⁷Cl by microwave spectroscopy. The NCl radical in the b ¹∑⁺ state was generated by de-glow discharge of a N₂/Cl₂ mixture. The rotational constant, centrifugal distortion constant, and quadrupole coupling constants of the Cl nucleus were determined. The observation of rotational transitions in the vibrationally excited v = 1 state made it possible to derive equilibrium structural parameters. A discussion on the internuclear potential of the three low-lying electronic states of NCl is given.