Zinc and cadmium dioxide anions are produced via electron capture of the corresponding neutral molecules during condensation of laser-ablated zinc and cadmium atoms with O-2 in excess neon at 4 K. Photosensitive infrared absorptions at 624.1 and 483.6 cm(-1) are assigned to the antisymmetric stretching vibrations (nu 3) of the linear ZnO2- and CdO2- anions on the basis of isotopic shifts and splittings as well as density functional calculations. The predicted quite low nu(3)/nu(1) ratios for both anions with (2)Pi(g) ground state are similar with the valence isoelectronic CO2+ and BO2 molecules. (C) 2010 Elsevier B. V. All rights reserved.