Structure and Reactivity of the Surface Methoxy Species on Ag{111}

Abstract

The structure and reactivity of the surface methoxy species on Ag{ 11 l} have been studied using a combination of reflection absorption infrared spectroscopy and temperature-programmed desorption. Methoxy can be generated by exposing a preoxidized Ag{ 11 l} surface to methanol at 180 K and adsorbs in an upright geometry possessing effective 3-fold symmetry, with its C-0 bond axis oriented normal to the surface at all coverages.This conclusion is based on a detailed symmetry analysis coupled with rigorous application of the metalsurface selection rule and careful assignment of the infrared absorption bands with the aid of deuterium substitution. It is shown that strong Fermi resonance interactions are the cause behind unusual features observed in the C-H stretching region of the infrared spectra of methoxy on many metal surfaces. Significant interadsorbate dipole coupling and chemicaUelectrostatic effects are responsible for the coverage-dependent frequency shifts exhibited by the infrared active bands. Methoxy is stable on Ag{ 11 11 up to 290 K, above which it decomposes to yield formaldehyde as the major product, which desorbs in a reaction-limited step that is consistent with first-order kinetics. Formate has been identified as a minor surface species when excess surface oxygen is present and acts as the intermediate in the further oxidation of formaldehyde to COZ and Hz.

Structural effects of ice grain surfaces on the hydrogenation of CO at low temperatures

“…The formation of H 2 CO and CH 3 OH with decreasing CO were observed in both samples. No peaks were observed around the wavenumbers reported for the peaks of HCO, CH 2 OH in N 2 and Ar matrix at 14 K [28,29] and CH 3 O on low temperature surface [30]. Although the absorption coefficients of those intermediate radicals are unknown, those coefficients are expected to be similar to those for H 2 CO and CH 3 OH.…”

Conversion of H2CO to CH3OH by Reactions of Cold Atomic Hydrogen on Ice Surfaces below 20 K

“…It can be clearly seen in Figure 6 that CH 3 OH molecules have formed and grown, as indicated by the emergence of peaks at 1032 and 1118 cm À1 and a weakening of the H 2 CO peaks at 1722, 1499, 1249, 1178, 2991, 2887, and 2832 cm À1 . No peaks were observed around the wavenumbers reported for the peaks of CH 3 O on the surface (Sim et al 1995) and CH 2 OH in the Ar matrix (Jacox 1981). Although the absorption coefficients of solid CH 3 O and CH 2 OH are unknown, we expect that the absorption coefficients are not far from that of CH 3 OH because those species have CÀO and/or OÀH bonds.…”

Laboratory Simulation of Competition between Hydrogenation and Photolysis in the Chemical Evolution of H2O‐CO Ice Mixtures

“…No peaks were observed around the wavenumbers reported for the peaks of CH 3 O on the surface (Sim et al 1995) and of CH 2 OH in the Ar matrix (Jacox 1981). Although the absorption coefficients of solid CH 3 O and CH 2 OH are unknown, we expect that the absorption coefficients are not far from that of CH 3 OH, because those species have CÀO and/or OÀH bonds.…”