REACTIONS OF LASER-ABLATED TITANIUM, ZIRCONIUM, AND HAFNIUM ATOMS WITH OXYGEN MOLECULES IN CONDENSING ARGON

Reactions of laser ablated Ti, Zr, and Hf atoms with oxygen molecules in a condensing argon stream gave the MO, MO(2), and M(2)O(2) molecules and MO(2)(-) molecular anions, which were identified from oxygen isotopic splittings and shifts. Simple self-consistent field, ECP calculations support the assignments to MO(2) and MO(2)(-) molecular species. The metal dioxide molecules have 113 +/- 5 degrees valence angles, while the molecular anions have 128 +/- 5 degrees valence angles. The M(2)O(2) molecules are probably nonplanar in contrast to the analogous more ionic alkaline earth metal species. A strong similarity between zirconium and hafnium oxide spectra was found. The observation of HfO and HfO2 stretching modes only 1-4 cm(-1) lower than ZrO and ZrO2 modes is due to a combination of lanthanide contraction and relativistic effects for hafnium.