Absorption spectrum of SO up to 2.5THz

Sulfur monoxide was produced in a radio frequency discharge of air in a cell containing pure sulfur. Together with the strong absorption signal of the main isotopologue, transitions of ^34^SO (^34^S: 4.21%) and ^33^SO (^33^S: 0.75%) were observed in natural abundance.

The newly observed transitions constitute an extension of the observed rotational quantum numbers of the molecule toward higher N values, allowing an improvement of the molecular parameters for the three species. An isotopically invariant fit has been performed based on pure rotational and ro-vibrational transitions of all SO isotopologues, enabling their accurate line position prediction at higher frequencies. Thanks to this new set of parameters, it is now possible to predict with very high accuracy the frequencies of the ro-vibrational lines.