THE NU-1 BAND OF (NO)2

The nu1 band of the NO dimer has been studied using a long-path (84 m) low-temperature (83.5 K) gas cell and a Fourier transform infrared spectrometer. Over 440 lines of (NO)2 have been measured in the 1840 to 1900 cm-1 region, with a resolution of 0.008 cm-1, and assigned to perpendicular (DELTAK(a) = +/-1) transitions with i and K(a) values up to 35 and 16, respectively. These measurements were analysed, along with the four previous microwave transitions, using an s-reduced asymmetric rotor Hamiltonian in order to obtain accurate rotational and quartic centrifugal distortion parameters for (NO)2 in its ground and upsilon1 = 1 vibrational states. As far as this experiment is concerned, the NO dimer behaves as a normal, planar, semi-rigid molecule, with no observed perturbations, only modest centrifugal distortion effects, and only small changes in parameters due to vibrational excitation. The observed intensities of (NO)2 lines were used to estimate a value for the dissociation energy of the dimer of D0 = 639 +/- 35 cm-1, where the indicated uncertainty depends mostly on an assumption that the vibrational transition moment of NO changes by 40% or less upon complex formation.