Knowledge Bank

Now that the first molecular anion, C$\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$, has been detected in the cold dark cloud TMC-1 and both this ion and C$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ detected in the circumstellar envelope IRC+10216 based on the laboratory work of Thaddeus and co-workers} \underline{\textbf{652}}, L141, 2006.}} \underline{\textbf{655}}, L57, 2007.}, it is of interest to study anew how anions are produced and destroyed via gas-phase reactions in interstellar and circumstellar environments. Relatively abundant anions are most likely formed principally by radiative attachment and depleted by photodetachment and ion-molecule reactions with atomic hydrogen and oxygen} \underline{\textbf{289}}, 656, 1981.}. New estimates of rate coefficients for some of these processes have been made. We have then included formation and depletion pathways for a number of molecular anions in the latest UMIST database for astronomy (http://www.udfa.net/). With this enhanced network, theoretical abundances and column densities of the anions in TMC-1 and IRC+10216 have been calculated. Our results will be discussed, along with our views on the most likely new anions to be detected once laboratory data become available.