Knowledge Bank

We are studying the pure rotational spectrum of the NO dimer, $(NO)2$. The dimers am produced using a continuous supersonic jet source, and probed using a mm-wave spectrometer based on harmonic multiplication. Microwave radiation (75-100 GHz) from a Gunn oscillator is multiplied ($\times 3$ or $\times 4$) in commercial tripler, focussed through the jet by Teflon lenses, and detected by a helium-cooled In Sb bolometer. The frequency scan and data collection are under microcomputer control. The computer also turns the jet off and on at intervals of 5 scans (about 5 sec), and automatically subtracts the background and sample spectra. Previously 4 rotational transitions of $(NO)2$= in the O to 23 GHz microwave region had been $reported.h$ Currently, we have measured about 80 new transitions in the frequency range from 227 To 382 GHz. with J values from 5 to 16, and $Ka$ values from 2 to 8. The underlying $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ hyperfine structure is partially resolved for some of the transitions, The observed line positions are quite well predicted by the existing molecular parameters from our analysis of the $\nu 1$ infrared band, but the new data will obviously allow a considerably more precise set of parameters to be derived. These new mm-wave results do not directly address the two great mysteries of the No dimer, namely the locations of the intermolecular vibrational mode and of he low-lying electronic states. We still hope to address the former mystery by means of long--path, low temperature FT spectroscopy in the far-ir region.