Behavior of chemical species in gas-metal interface observed in-situ with polarization modulation infrared absorption and emission spectroscopies

Abstract

The polarization modulation (PM) technique has been successfully applied for observing in-situ the infrared spectra of species on metal surfaces in a gaseous medium at room temperature. Unidentate and bridged formates as well as physically adsorbed formic acid were detected on copper surfaces in formic acid vapor. Introduction of formaldehyde vapor on copper surfaces resulted in a reaction intermediate of dioxymethylene in addition to the unidentate formate and physically adsorbed formaldehyde as surface species. The molecular orientation of these species is discussed. Because the PM technique eliminates the spontaneous emission from surface species, it provides us with undeformed absorption spectra of surface species at elevated temperatures. Metastable surface species of methoxy and Mo(V)=O groups were detected at 473 K on a thin film of MoO 3 in methanol vapor. The PM technique is effective also for improving the S/N ratio of infrared emission spectra of thin films on metal surfaces. The reduction of MoO 3 thin films with hydrogen gas was investigated by means of PM infrared emission spectroscopy.