Isotopic abundance ratios in interstellar carbon monosulfide

A survey of the relative abundances of the isotopic species, (C-12)(S-32), (C-12)(S-34), and (C-13)(S-32) has been made in 14 dense molecular clouds through observations of the J = 2-1 rotational transitions at 3 mm. The abundance ratio, (C-13)(S-32)/(C-12)(S-34), 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 + or - 0.10 where the quoted error is the rms of the source-to-source fluctuations. The average disk value for C-13/C-12 is 0.015, if S-32/S-34 is terrestrial. No evidence is found for a systematic variation of the ratio within the disk itself.