The rotational spectrum of protonated sulfur dioxide, HOSO +

Aims. We report on the millimeter-wave rotational spectrum of protonated sulfur dioxide, HOSO + . Methods. Ten rotational transitions between 186 and 347 GHz have been measured to high accuracy in a negative glow discharge. Results. The present measurements improve the accuracy of the previously reported centimeter-wave spectrum by two orders of magnitude, allowing a frequency calculation of the principal transitions to about 4 km s −1 in equivalent radial velocity near 650 GHz, or one linewidth in hot cores and corinos. Conclusions. Owing to the high abundance of sulfur-bearing molecules in many galactic molecular sources, the HOSO + ion is an excellent candidate for detection, especially in hot cores and corinos in which SO2 and several positive ions are prominent.