The pure rotational spectra of the bicyclic aromatic nitrogen heterocycle molecules, quinazoline, quinoxaline, and phthalazine, have been recorded and assigned in the region 13-87 GHz. An analysis, guided by ab initio molecular orbital predictions, of frequency-scanned Stark modulated, jet-cooled millimeter wave absorption spectra (48-87 GHz) yielded a preliminary set of rotational and centrifugal distortion constants. Subsequent spectral analysis at higher resolution was carried out with Fourier transform microwave (FT-MW) spectroscopy (13-18 GHz) of a supersonic rotationally cold molecular beam. The high spectral resolution of the FT-MW instrument provided an improved set of rotational and centrifugal distortion constants together with nitrogen quadrupole coupling constants for all three species. Density functional theory calculations at the B3LYP/6-311+G** level of theory closely predict rotational constants and are useful in predicting quadrupole coupling constants and dipole moments for such species.
McNaughton, D., Godfrey, P., Jahn, M., Dewald, D., & Grabow, J-U. (2011). Fourier transform microwave and millimetre wave spectroscopy of quinazoline, quinoxaline, phthalazine. Journal of Chemical Physics, 134(15), 1 - 4. https://doi.org/10.1063/1.3580770