We have developed a Laser Raman-Ellipsometry combined system to analyze solid surfaces in situ under chemical reactions. Reaction products in gas phase are analyzed by a mass spectrometer, a surface layer formed by the reaction is analyzed by an Ellipsometer, and surface species by a Raman spectrometer. The system is applied to study the dissociative reaction of CO gas on an iron surface under 1 atm. pressure. C and O atoms from CO gas diffuse into the interior of the Fe to form a diffusion layer, whose thickness and dielectric constant are determined. After formation of the diffusion layer of 11 nm an Fe
3O
4 oxide formation occurs from the surface. We have found that the Fe
3O
4 layer of 16 nm generates the A
1g phonon mode at 672cm
-1 compared with 675cm
-1 from a bulk Fe
3O
4. Two kinds of surface Raman bands induced from CO adsorbed on the Fe
3O
4 are observed at 1121cm
-1 and 1812cm
-1, respectively, which seem to be surface-enhanced. It is concluded that the system is a very powerful tool to study solid surfaces under chemical reaction conditions.
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