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.