REACTIONS OF PULSED-LASER EVAPORATED CA, SR, AND BA ATOMS WITH O-2 - INFRARED-SPECTRA OF THE METAL-OXIDES, OXIDE DIMERS, DIOXIDES, AND PEROXIDES IN SOLID ARGON

Pulsed-laser ablated Ca, Sr, and Ba atoms have been reacted with O-2 i n excess argon during condensation at 10 K. Infrared spectra and oxyge n isotopic substitution show that the major products are the symmetric al OMO metal dioxide and the rhombic metal oxide dimer. The metal oxid es and cyclic MO(2) peroxides are minor products. In the case of calci um, activation energy provided by pulsed-laser ablation makes the reac tion to give CaO, CaO2, (CaO)2, and OCaO possible. Strontium and bariu m are more reactive and the dioxides and peroxides increase on anneali ng the argon matrix to 25 K, which shows that no activation energy is necessary for the Sr and Ba atom reactions with O-2. Photolysis decrea sed the peroxide in favor of the dioxide species. The alkaline earth m etal peroxides are characterized by O-O stretching absorptions in the 700-cm(-1) region and are distinctly different from the alkali metal s uperoxides, which are characterized by O-O stretching absorptions in t he 1100-cm(-1) region.