An EELS study of the oxidation of H2CO on Ag(110)

Raman spectra of aqueous solutions containing up to 40 mol% of formaldehyde were recorded in the 120–4000 cm −1 spectral range. The water vibrational modes are not too heavily modified by the presence of the polymerized species in the aqueous solutions. The intensity of the bands corresponding to the C–O and C–H vibrational modes depends on the water content. Two bands are found for the C–O symmetric and antisymmetric stretching modes. The first is related to the C–O–C groups formed within the oligomer chains as the condensation increases and the second to the C–OH groups located at the end of the oligomer chains. A change in the intensity evolution of the bands corresponding to the stretching modes of the C–O–C groups occurs above 15 mol% formaldehyde concentration, corresponding to the formation of the HO(CH2O)nH oligomers with n ≥ 3. The intensity of the stretching modes due to the C–OH groups varies linearly with concentration. A linear variation of the band intensity of the CH modes as a function of formaldehyde content is also observed. Copyright  2003 John Wiley & Sons, Ltd.

Raman analysis of formaldehyde aqueous solutions as a function of concentration

The adsorption of formic acid (HCOOH) on the Si(100)c(4×2), Si(100)(2×1), Si(100)9° vicinal and Si(111)(7×7) surfaces has been studied by means of high resolution electron energy loss spectroscopy. Formic acid is partially dissociated to form the unidentate formate species (HCOO) and H adatoms on these surfaces at both 90 and 300 K. The formate species is bonded to the Si surface with a covalent bond formed between one of its oxygen atoms and the dangling bond of the surface Si atom. A condensed multilayer of molecular formic acid is formed after the Si surface is saturated with the formate species at 90–150 K. The thermal decomposition mechanism has been studied in detail. The decomposition temperatures of the formate species on Si(100) and Si(111) are ∼600 and 550 K, respectively. It appears that the surface steps do not play an important role in the Si–HCOOH interaction. As the formate‐covered surface is exposed to atomic hydrogen, methylendiolate (H2COO) is formed on the Si surface.

The adsorption and thermal decomposition of formic acid on Si(100) and Si(111) surfaces

The reactions of methane and methanol species with excited atomic oxygen generated by ozone have been examined in low temperature argon matrices. The major product of the CH 4 +O( 1 D) reaction was CH 3 OH, confirming a previous prediction of the intermediary of CH 3 OH to the first product in the gas phase reaction. Insertion of an O atom in a CH or CD bond was found to give a similar result. On the basis of kinetic studies two major pathways were observed for the CH 3 OH+O( 1 D) reaction. The first one led to H 2 O and CH 2 O and the second one to methanediol by insertion of an O atom in a CH bond. H 2 O and CH 2 O arise from an intermediate not isolated. Experiments with oxygen-18 and deuterated methanol suggest either an abstraction of a hydroxyl H atom by O( 1 D) or an insertion of atomic oxygen in the OH bond. A weak complex between methanol and ozone was identified, but it did not play a particular role in the reaction.

Masanori Yamamoto

Papers

Raman spectra and normal vibrations of methylene glycol and its perdeuterated analogue