Millimeter-wave spectroscopy of OSSO

Sulfur is the element with the largest number of known binary oxides\footnote{Steudel, \textit{Top. Curr. Chem.} 231, 203--230 (2003)} and as such has attracted the curiosity of chemists and physicists for decades. In particular, the simpler ones are of great interest for diverse scientific disciplines like structural and theoretical chemistry, astrochemistry, atmospheric chemistry and molecular physics. Out of those, the simplest sulfur rich oxides and dioxides S$_2$O and S$_2$O$_2$ have been studied spectroscopically to some extent in the past\footnote{Thorwirth et al., \textit{J. Mol. Struct.} 795, 1-3 (2006), and refs. therein} but still pose challenging problems to future gas-phase investigations. In the present study, the pure rotational spectrum of S$_2$O$_2$ has been investigated in the ground and $\nu_3$ states. In addition, ground state transitions of OS$^{34}$SO were observed. OSSO was produced in a radio frequency discharge through SO$_2$. Experimental measurements have been supported by high-level CCSD(T) calculations. An extensive set of molecular parameters has been derived