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 spectrometric experiments, such as collisional activation of carboxylate ions or double electron transfer to CO2+.. In particular, it is shown that vibrational excitation of the precursor cations increases the yield of the bound anion radicals in charge inversion experiments. Combined application of experimental and theoretical means indicates that for bent geometries, the (2)A(1) state of the carbon dioxide anion radical is stable against electron detachment in the mu s timescale of the experiments. In a chemical sense, the CO2-. anion radical can be regarded as an activated carbon dioxide unit in which the C-O bonds are weakened and the carbon center exhibits distinct radical character. Thus, CO2-. constitutes a new type of distonic anion in which the charge and the unpaired electron are located in different symmetry planes. (Int J Mass Spectrom 185/186/187 (1999) 25-35) (C) 1999 Elsevier Science B.V.