IR spectra of ozone adsorbed on MgO

Abstract

The IR spectra of O₃ adsorbed on polycrystalline (high surface area) MgO are reported and assigned. Two distinct groups of absorptions in the 1160–970 and 1730–1170 cm⁻¹ spectral regions were observed. The bands falling in the first region, fully reversible upon decreasing the O₃ pressure, are grouped into two doublets with components at 1105–1024 cm⁻¹ (A₁–A₃ doublet) and at 1140–1038 cm⁻¹ (B₁–B₃ doublet). The A₁–A₃ doublet is assigned to the stretching modes (ν_sym and ν_asym respectively) of O₃ adsorbed through a terminal oxygen atom on Mg²⁺_5c ions exposed on the extended {001} terminations of the MgO microcrystals. The less intense B₁–B₃ doublet at 1140–1038 cm⁻¹ is assigned to the stretching modes of O₃ adsorbed on defective positions like edges, corners and steps. The irreversible bands in the 1730–1170 cm⁻¹ range are assigned to oxidation products formed by reaction of O₃ with carbonaceous impurities remaining on the MgO surface after the activation in vacuo at high temperature. In particular the doublet at 1690–1280 cm⁻¹ is assigned to the ν_asym and ν_sym stretching modes of bidentate carbonate-like species. The bathochromic shifts of the A₁–A₃ components with increasing O₃ coverage are interpreted in terms of lateral dipole–dipole interactions (of both static and dynamic nature) between the adsorbed species. The negative shift of the ν_asym mode of the carbonate-like species induced by the increase in the O₃ coverage is ascribed to lateral interactions of the static type.