Laser ablation of transition metals with concurrent codeposition of C2H2/O-2/Ar mixtures at 11 K produced metal independent absorptions at 1493.1 cm(-1). On the basis of isotopic shifts and splittings, enhancement in doping with electron trapping gas, and quantum chemical frequency calculations, the band is assigned to the O-O stretching vibration of the C2H2O2+ cation, which was predicted to have a (2)A" ground state with a nonplanar C-s symmetry. (C) 2003 American Institute of Physics.