Millimeter-Wave Spectrum of the NO Dimer

Area of Science:

• Molecular Spectroscopy
• Physical Chemistry
• Chemical Physics

Background:

• The pure rotational spectrum of the nitrogen monoxide (NO) dimer was previously limited to a few microwave transitions.
• Understanding the rotational dynamics and intermolecular potential of dimers is crucial in molecular physics.

Purpose of the Study:

• To investigate the pure rotational spectrum of the NO dimer ((14N16O)2) in the millimeter-wave region.
• To significantly improve the ground state parameters of the NO dimer by adding new spectral data.

Main Methods:

• Direct absorption spectroscopy was employed in a supersonic jet expansion.
• Measurements were conducted in the 225-400 GHz millimeter-wave frequency range.
• Data analysis combined new millimeter-wave transitions with existing microwave and infrared data.

Main Results:

• 66 new millimeter-wave transitions for the NO dimer were measured, with J values from 4 to 16 and Ka from 2 to 7.
• Most transitions appeared as single lines, with some exhibiting partially resolved hyperfine structure.
• An improved set of ground state parameters was obtained, including the first sextic distortion parameters.

Conclusions:

• The study significantly enhanced the characterization of the NO dimer's ground state properties.
• The inclusion of millimeter-wave data provided a more precise determination of the dimer's rotational constants and distortion parameters.