INFRARED DIODE-LASER SPECTRA OF THE NU(9) AND NU(11) N-O STRETCHING BANDS

The rotationally resolved jet-cooled infrared spectra of the b-type nu (9) (b(2u)) fundamental band at 1757 cm(-1) and the a-type nu(11) (b(3 u)) fundamental band at 1261 cm(-1) of the N-O stretches of N2O4 have been recorded with a diode laser. The vg band was found to be unpertur bed, and it was possible to assign nearly 100% of the observed lines w ith-a signal to noise greater than 2. In contrast, most of the K-a sta tes of the nu(11) band were found to be strongly perturbed. A large nu mber of strong lines (approximate to 20%) are unassigned and presumabl y arise from the perturbing state as well as torsional hot band transi tions. The rotational analysis yields precise spectroscopic constants for the ground vibrational state which are interpreted in terms of a p lanar centrosymmetric dimer with a N-N bond length of 1.756(10) Angstr om. The observed nuclear-spin statistical weights and near-zero inerti al defect are consistent with the planar centrosymmetric structure det ermined in earlier electron-diffraction studies.