Millimeter-wave spectrum of the NO dimer

The pure rotational spectrum of the NO dimer, ((NO)-N-14-O-16)(2), has been studied in the 225-400 GHz millimeter-wave region by means of direct absorption in a supersonic jet expansion. Previously, only 4 rotational transitions of (NO)(2) had been measured in the microwave region. To these, we have added 66 new millimeter-wave transitions with values of J ranging from 4 to 16 and of K-a, from 2 to 7. Most transitions were observed as single lines, but a few showed partially resolved hyperfine structure. The analysis of these data, in combination with the previous microwave transitions and an extensive set of infrared (nu(1), band) measurements, has resulted in a greatly improved set of parameters for the ground state of the NO dimer, including the first sextic distortion parameters. (C) 1997 Academic Press.