IR spectra of ozone adsorbed on MgO

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 (νsym and νasym 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 νasym and νsym 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 νasym mode of the carbonate-like species induced by the increase in the O3 coverage is ascribed to lateral interactions of the static type.