In situ Raman spectroscopy has been used to show that peroxide ions are present on Ba/MgO catalysts at temperatures up to 800 OC. The surface 0z2ions are believed to be responsible for the activation of CH4 during the oxidative coupling reaction which occurs at these elevated temperatures. At 100 OC the peroxide ion spectrum is characterized by a major line at 842 cm-l, with minor peaks at 829 and 821 cm-l. As the temperature was increased, all of the peaks shifted to lower wavenumbers and broadened, until at 800 OC only a broad asymmetric band remained. Introduction of l 8 0 z also caused the peaks to shift to lower wavenumbers, consistent with the assignment of the spectra to peroxide ions. In the presence of COz and H20 the 0z2ions reacted to form carbonate ions at T 1 500 OC, which is in agreement with the poisoning effect of C02 in the catalytic experiments. At Ba loadings 5 2 mol ?6 a two-dimensional layer of BaOz is present on the surface of MgO, but at larger loadings crystallites of BaOz contribute significantly to the Raman spectra. e Abstract published in Aduance ACS Absrracrs. November 15, 1993.Estonia.

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The Raman spectra of barium peroxide (BaO 2 ) in the O-O stretching region were studied at various temperatures between 22 and 850°C in both O 2 and He atmospheres. Although only one peroxide stretching band is expected for the crystal symmetry, three Raman bands, which were assigned to peroxide ions in different crystal environments due to the relative locations of oxide impurities, were observed at all temperatures. The temperature dependencies of the Raman frequencies, bandwidths, and the absolute and partial intensities were investigated in detail, and these were explained on the basis of the sample composition and structural changes.

The infrared and Raman spectra of bicyclo[3.3.0]oct-1,5-ene in the vapor and liquid phases have been recorded and analyzed. Ab initio calculations, including those with the triple-ζ (cc-pvtz) basis set, have been carried out to predict the energy differences between five different structural forms. Both the spectra and ab initio calculations show that the cis C 2V conformation is the lowest energy form. The trans C 2h structure is predicted to lie only 65 to 229 cm -1 higher in energy, depending on whether the effects of ring flapping are considered, but spectroscopic evidence for this conformation is limited. The dihedral angle of puckering is calculated to be 26°, which is the same as the cyclopentene value.