Infrared spectra of transition-metal dioxide anions: MO2- (M = Rh, Ir, Pt, Au) in solid argon.

Transition-metal dioxide anions RhO(2)(-), IrO(2)(-), PtO(2)(-), and AuO(2)(-) were produced from cocondensation of laser-ablated metal atoms and electrons with dioxygen in excess argon at 6 K. Photosensitive absorptions were assigned to the antisymmetric stretching vibration (nu(3)) of the metal dioxide anions from isotopic shifts and splittings as well as theoretical frequency calculations. On the basis of the observed nu(3) vibrational frequencies for M(16)O(2) and M(18)O(2), the anions are estimated to be linear or near linear. Density functional calculations at the DFT/B3LYP level predicted that the third-row transition-metal dioxide anions IrO(2)(-), PtO(2)(-), and AuO(2)(-) have singlet, doublet, and triplet ground states with linear structures, while the RhO(2)(-) anion was predicted to have a slightly bent geometry.