Reactions of Laser-Ablated Niobium and Tantalum Atoms with Oxygen Molecules:  Infrared Spectra of Niobium and Tantalum Oxide Molecules, Anions, and Cations

Abstract

Laser-ablated niobium and tantalum atoms react with O 2 to give MO, MO 2, MO 2 -, and MO 2 + products, which are identified from oxygen isotopic substitution on their matrix infrared spectra and from DFT calculations of isotopic frequencies. Annealing allows diffusion and further reaction to form (O 2 )MO 2 complexes, which are characterized by four fundamentals. On the basis of the ν 3 vibrational frequencies for the M 16 O 2 and M 18 O 2 isotopic molecules, the metal dioxide valence angles are estimated to be 108 ± 5° for NbO 2 and 106 ± 5° for TaO 2; the molecular cations have the smaller valence angles 103 ± 5° and 105 ± 5° for NbO 2 + and TaO 2 +, respectively, and the molecular anions are more open with 120 ± 10° valence angles. Evidence is also presented for stable MO 3 - anion species.