The millimeter- and submillimeter-wave spectrum of methyl mercaptan (CH3SH)

Methyl mercaptan (CH3SH), a threefold internal rotor and the sulfur analog of methanol, has been detected in the interstellar medium, although little is known about its chemistry or about the physical conditions most favorabl e for its synthesis. Until the present, the assigned and fitted rotational- torsional spectral lines of methyl mercaptan have been mainly confined to t ransitions involving low rotational quantum numbers. We have measured many new lines of the rotational spectrum of this species through the rotational quantum number J = 20 using two spectrometers: our standard klystron-based system and a new fast scan submillimeter spectroscopic technique (FASSST). The newly measured lines have been combined with previous data at mainly l ower frequencies to form a data set consisting of approximately 1000 lines that has been fitted to nearly the accuracy of our experiments using the in ternal axis method we have previously applied to methanol. The spectral con stants obtained from the fit have allowed us to predict the frequencies of many additional lines up to 600 GHz in frequency and up to J = 25 in rotati onal quantum number.