On the formation of the carbon dioxide anion radical CO2-. in the gas phase

Although carbon dioxide is well known to have a negative electron affinity, the CO2-. anion radical can be generated in several types of mass spectrom etric experiments, such as collisional activation of carboxylate ions or do uble electron transfer to CO2+.. In particular, it is shown that vibrationa l excitation of the precursor cations increases the yield of the bound anio n radicals in charge inversion experiments. Combined application of experim ental and theoretical means indicates that for bent geometries, the (2)A(1) state of the carbon dioxide anion radical is stable against electron detac hment in the mu s timescale of the experiments. In a chemical sense, the CO 2-. anion radical can be regarded as an activated carbon dioxide unit in wh ich the C-O bonds are weakened and the carbon center exhibits distinct radi cal character. Thus, CO2-. constitutes a new type of distonic anion in whic h the charge and the unpaired electron are located in different symmetry pl anes. (Int J Mass Spectrom 185/186/187 (1999) 25-35) (C) 1999 Elsevier Scie nce B.V.