Millimeter and submillimeter spectroscopy of chlorine nitrate: The CI quadrupole tensor and the harmonic force field

The rotational spectra of (ClONO2)-Cl-35 and (ClONO2)-Cl-37 in their ground and first excited torsional states (v(9) = 1) have been reinvestigated in selected regions between 84 and 441 GHz. An extensive set of spectroscopic constants has been determined, enabeling more accurate predictions of line positions in the submillimeter region. Accidental near-degeneracies of rotational levels cause perturbations of the quadrupole patterns, allow the observation of a Delta J = 2 transition, and result in the precise determination of chi(ab). The quartic distortion constants along with the vibrational wavenumbers and inertial defect differences have been used for a calculation of the harmonic force field. The assignments of the vibrational modes in terms of internal coordinates are discussed. The results are compared with properties of related molecules such as Cl2O. (C) 1997 Academic Press.