Negatively-charged clusters. of carbon dioxide, (CO2)(n)(-), react with NO to form anions with [(CO2)(m)(NO)](-) stoichiometry. The chemical identity of [(CO2)(m)(NO)](-) is probed by photoelectron spectroscopy; the vertical detachment energy of the smallest product anion, [(CO2)(NO)](-), is determined to be 3.72 +/- 0.04 eV. With the aid of ab initio calculations, [(CO2)(NO)](-) is further identified as O2CNO-((1)A') having a covalent C-N linkage between the CO2 and NO units. These findings demonstrate that (1) (CO2)(n)(-) behaves as a CO2- radical anion in the gas-phase chemistry, and that (2) the relevant reaction proceeds as a radical addition process, CO2- + NO -> O2CNO-((1)A'). (c) 2006 Elsevier B.V. All rights reserved.