Rotational spectroscopy and dipole moment of cis-cis HOONO and DOONO

The rotational spectrum of cis-cis HOONO has been studied over a broad range of frequencies, 13–840 GHz, using pulsed beam Fourier-transform microwave spectroscopy and room-temperature flow cell submillimeter spectroscopy. The rotational spectrum of the deuterated isotopomer, cis-cis DOONO, has been studied over a subset of this range, 84–640 GHz. Improved spectroscopic constants have been determined for HOONO, and the DOONO spectrum is analyzed for the first time. Weak-field Stark effect measurements in the region of 84–110 GHz have been employed to determine the molecular dipole moments of cis-cis HOONO $[μa=0.542(8)D,μb=0.918(15)D,μ=1.07(2)D]$ and DOONO $[μa=0.517(9)D,μb=0.930(15)D,μ=1.06(2)D]$⁠. The quadrupole coupling tensor in the principal inertial axis system for the $N14$ nucleus has been determined to be $χaa=1.4907(25)MHz,χbb=−4.5990(59)MHz,χab=3.17(147)MHz$⁠, and $χcc=3.1082(59)MHz$⁠. Coordinates of the H atom in the center-of-mass frame have been determined with use of the Kraitchman equations, $∣aH∣=0.516Å$ and $∣bH∣=1.171Å$⁠. The inertial defects of HOONO and DOONO are consistent with a planar equilibrium structure with significant out-of-plane H atom torsional motion. Comparisons of the present results are made to ab initio calculations.