REACTIONS OF LASER-ABLATED NIOBIUM AND TANTALUM ATOMS WITH OXYGEN MOLECULES - INFRARED-SPECTRA OF NIOBIUM AND TANTALUM OXIDE MOLECULES, ANIONS, AND CATIONS

Laser-ablated niobium and tantalum atoms react with O-2 to give MO, MO 2, MO2-, and MO2+ products, which are identified from oxygen isotopic substitution, on their matrix infrared spectra and from DFT calculatio ns of isotopic frequencies. Annealing allows diffusion and further rea ction to form (O-2)MO2 complexes, which are characterized by four fund amentals, On the basis of the nu(3) vibrational frequencies for the (M O2)-O-16 and (MO2)-O-18 isotopic molecules, the metal dioxide valence angles are estimated to be 108 +/- 5 degrees for NbO2 and 106 +/- 5 de grees for TaO2; the molecular cations have the smaller valence angles 103 +/- 5 degrees and 105 +/- 5 degrees for NbO2+ and TaO2+, respectiv ely, and the molecular anions are more open with 120 +/- 10 degrees va lence angles. Evidence is also presented for stable MO3- anion species .