A search for MgNC and AlNC in TMC-1: the status of metals in dark cloud cores.
TURNER B.E., PETRIE S., DUNBAR R.C. and LANGSTON G.
Abstract (from CDS):
Heavy metals in the gas phase are important in controlling the ionization of a cold dark cloud and hence the chemistry and finally the cloud evolution. Two of us (S. P. and R. C. D.) earlier suggested a fast radiative association mechanism to form MgNC and AlNC in TMC-1. We have conducted a sensitive search with the Green Bank Telescope (GBT) for both species in TMC-1. The upper limit for the fractional abundance of MgNC is 1.2x10–11. We have run detailed models of the chemistry, which include high and low metal content, three values of C/O, and three values of density. The models include the time dependence up to 1x108 yr. Most of the models predict that we should have seen MgNC. We compare the conditions in TMC-1 with those for IRC +10216, in which MgNC and AlNC are both detected. We conclude that in IRC +10216 the chemistry favors a high abundance of both atomic Mg+ and cyanopolyynes, the two reactants that form MgNC, and that these reactants are less favored in TMC-1.