Carbon isotope fractionation and depletion in TMC1
  12C/13C 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 in several species hosting more than one carbon
atom, i.e. CCH, CCS, CCCS and HC$_3$N. Here we work to ascertain whether these
isotopologic anomalies actually result from the predicted depletion of the 13C+
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 \HH CS at
three positions in Taurus(TMC1, L1527 and the ammonia peak) using the ARO 12m
telescope. We saw no evidence of 12C/13C anomalies in our observations.
Although the pool of C+ is likely to be depleted in 13C 13C 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.
