Transitions between Hund's coupling cases for the X ²Π state of NO

Abstract

The submillimetre-wave spectra of ¹⁴N¹⁶O, ¹⁵N¹⁶O, and ¹⁴N¹⁸O in both the X ²Π_1/2 and X ²Π_3/2 states have been measured in the frequency region 773 GHz to 1.1 THz and assigned. Transitions involving J values between 6.5 and 10.5 have been recorded for the first time. The higher J values display an uncoupling of the electronic spin S and the angular momentum L from the rotor axis. The S-uncoupling leads to an intermediate coupling condition between Hund's case (a) and (b), whereas the L-uncoupling causes a coupling scheme intermediate between Hund's case (a) and (d). An improved set of molecular parameters has been obtained for these isotopic species, including magnetic dipole and electric quadrupole constants.