Rotational Spectroscopy of Isotopologues of Silicon Monoxide, SiO, and Spectroscopic Parameters from a Combined Fit of Rotational and Rovibrational Data

Pure rotational transitions of silicon monoxide, involving the main (28Si16O) as well as several rare isotopic species, were observed in their ground vibrational states by employing long-path absorption spectroscopy between 86 and 825 GHz (1 ≤ J″ ≤ 18). Fourier transform microwave spectroscopy was used to study the J″ = 0 transition frequencies in the ground and several vibrationally excited states. The vibrational excitation of the newly studied isotopologues extend to between υ = 9 and 29 for 28Si17O and 30Si16O, respectively. Data were extended for some previously investigated species up to υ = 51 for the main isotopologue. The high spectral resolution allowed us to resolve the hyperfine structure in 28Si17O caused by the nuclear electric quadrupole and magnetic dipole moments of 17O for the first time, and to resolve the much smaller nuclear spin-rotation splitting for isotopic species containing 29Si. These data were combined with previous rotational and rovibrational (infrared) data to determine an improved set of spectroscopic parameters of SiO in one global fit which takes the breakdown of the Born–Oppenheimer approximation into account. Highly accurate rotational transition frequencies for this important astronomical molecule can now be predicted well into the terahertz region with this parameter set. In addition, a more complete comparison among physical properties of group 14/16 diatomics is possible.