CARBON ISOTOPE FRACTIONATION AND DEPLETION IN TMC1

C-12/C-13 isotopologue abundance anomalies have long been predicted for gas-phase chemistry in molecules other than CO and have recently been observed in the Taurus molecular cloud (TMC) in several species hosting more than one carbon atom, i.e., CCH, CCS, CCCS, and HC3N. Here we work to ascertain whether these isotopologic anomalies actually result from the predicted depletion of the C-13(+) ion in an oxygen-rich optically shielded dense gas, or from some other more particular mechanism or mechanisms. We observed lambda 3mm emission from carbon-, sulfur-, and nitrogen-bearing isotopologues of HNC, CS, and H2CS at three positions in Taurus (TMC1, L1527, and the NH3 peak) using the ARO 12 m telescope. We saw no evidence of C-12/C-13 anomalies in our observations. Although the pool of C+ is likely to be depleted in C-13, C-13 is not depleted in the general pool of carbon outside CO, which probably exists mostly in the form of C-0. The observed isotopologic abundance anomalies are peculiar to those species in which they are found.