Reactions of Pulsed-Laser Evaporated Ca, Sr, and Ba Atoms with O2. Infrared Spectra of the Metal Oxides, Oxide Dimers, Dioxides, and Peroxides in Solid Argon

Abstract

Pulsed-laser ablated Ca, Sr, and Ba atoms have been reacted with 0 2 in excess argon during condensation at 10 K. Infrared spectra and oxygen isotopic substitution show that the major products are the symmetrical OM0 metal dioxide and the rhombic metal oxide dimer. The metal oxides and cyclic M02 peroxides are minor products. In the case of calcium, activation energy provided by pulsed-laser ablation makes the reaction to give CaO, CaO2, (CaO)2, and OCaO possible. Strontium and barium are more reactive and the dioxides and peroxides increase on annealing the argon matrix to 25 K, which shows that no activation energy is necessary for the Sr and Ba atom reactions with 02. Photolysis decreased the peroxide in favor of the dioxide species.The alkaline earth metal peroxides are characterized by 0-0 stretching absorptions in the 700-cm-1 region and are distinctly different from the alkali metal superoxides, which are characterized by 0-0 stretching absorptions in the 1 lOO-cm-' region.

Infrared Spectra and Quantum Chemical Calculations of Group 2 MO2, O2MO2, and Related Molecules

“…The presence of a cation requires an anion and O 3 -is also observed at 792.4 cm -1 in the solid nitrogen matrix and O 4 -was observed in the argon matrix studies. 2 The present DFT calculations (Table 7) provide more theoretical support for identification of several bands observed in the earlier Be + O 2 reactions in condensing argon. 8 Two bands labeled K at 1288.9 and 1264.1 cm -1 increased on photolysis, revealed 1/2/1 mixed isotopic triplets for two equivalent O atoms, and exhibited 16/18 ratios (1.0168, 1.0175) appropriate for a symmetric Be-O 2 stretching mode.…”

“…[4][5][6] Recent infrared studies of pulsed laser evaporated alkaline-earth metal atoms and oxygen in argon have shown that the dioxide is the major product. 2 However, in preliminary nitrogen studies, calcium peroxide appears to be the major product formed, and a complete study of group 2 atom reactions with O 2 in nitrogen has been done in order to more fully characterize these peroxide molecular species. Complimentary quantum chemical calculations have been done to further characterize these novel product species.…”

The vibrational frequencies of CaO 2 , ScO 2 , and TiO 2 : a comparison of theoretical methods

“…Thus the CCSD(T) approach should yield the most accurate harmonic frequencies available to date, and therefore we compare the other methods to this approach. Consistent with this expectation, the CCSD(T) x 3 harmonic frequency is in reasonable agreement with the m 3 fundamental observed in solid argon [32]. The HF, B3LYP, B3PW91, and CASSCF approaches are in good agreement with the CCSD(T).…”

“…On the basis of the results for three states of CaO 2 , one would probably pick one of the two hybrid approaches as the method of choice, as they work for all three states and are in good agreement with the available CCSD(T) and experimental fundamentals in solid argon [32] or nitrogen [23]. The failure of BP86 for the 3 B 2 state and MP2 for the 3 B 2 and 3 A 2 states would appear to make these approaches less desirable for these systems.…”

“…Bond lengths are in A Ê , angles are in degrees, harmonic frequencies in cm A1 , intensities are in km/mol, and energy separations are in kcal/mol a The C s structure is 0.01 kcal/mol below the C 2v b Ref. [32] c The geometry is taken from the B3LYP approach d Ref. [23], the most intense absorbance has been set to 100 for CaO 2 , yields a C 2m solution, with vibrational frequencies in reasonable agreement with the CCSD(T); the biggest dierence being that the BP86 frequency for the b 2 mode is 62 cm A1 lower than the CCSD(T), and both are much lower than the 722 cm A1 experimental value [10].…”