Isotopic abundance ratios in interstellar carbon monosulfide

A survey of the relative abundances of the isotopic species, 12C32S, 12C34S, and 13C32S has been made in 14 dense molecular clouds through observations of the J=3-1 rotational transitions at 3 mm. The abundance ratio, [13C32S]/[12C34S], is found to be 1.9 times greater in the galactic center sources than in the galactic disk sources. The average ratio for the galactic disk sources is 0.35 +- 0.10 where the quoted error is the rms of the source-to-source fluctuations. The average disk value for [13C]/[12C] is 0.015, if [32S]/[34S] is terrestrial. No evidence is found for a systematic variation of the ratio within the disk itself. Terrestrial sulfur abundances would imply that either the observations in CS are spatially unresolved or the kinetic temperature for CS is lower than that for CO. Beam dilution factors are derived for the sources studied. In addition, values for the molecular hydrogen densities and CS fractional abundances are obtained for these sources