Knowledge Bank

Following the initial detection of the pure sulfur clusters $S3$ and $S4$ at centimeter wavelengths by Fourier transform microwave $spectroscopya$, $S3$ has subsequently been observed at millimeter wavelengths. Thirteen spectroscopic constants reproduce over 60 transitions of $S3$ between 9 and 460 GHz (with $J\le 87$ and $Ka\le 7$) to within the measurement uncertainties. From these the frequencies of the astrophysically relevant lines of $S3$ can be calculated to about 1 part in $107$ up to 500 GHz, allowing deep searches in the atmosphere of Io, dense molecular cores, and circumstellar shells of late-type stars with existing millimeter- and submillimeter-wave telescopes.