[en] When sodium is burned at high temperature in the atmosphere, it reacts simultaneously with H₂O in the atmosphere so that it can produce high temperature melt of sodium hydroxide as a solvent. If this melt includes peroxide ion (O₂^2-), it will be a considerably active and corrosive for iron so that several sodium iron double oxides will be produced as corrosion products after the reaction with steel structures. The present study was carried out in order to investigate the ability of presence of peroxide ion in sodium hydroxide solvent at high temperature and that of identification of the several corrosion products using laser Raman spectroscopy. The measurement system with ultraviolet laser was developed simultaneously in the present work to improve the ability of the measurement at high temperature. As results from the measurements, the possibility of the presence of peroxide ion was shown up to 823K in sodium peroxide and 823K in the melt of sodium hydroxide mixed with sodium peroxide. As for superoxide ion, the possibility of the presence was showed up to 873K in potassium superoxide and up to 773K in the melt of sodium hydroxide mixed with potassium superoxide. As a result from consideration, it was concluded that superoxide ion will not change into peroxide ion in sodium hydroxide solvent at high temperature. On the basis of the above results, it was concluded that the possibility of presence of peroxide ion was shown as a corrosive chemical species in the molten sodium hydroxide at high temperature and this gave an evidence for the reaction mechanism of 'melting salt type corrosion'. As for sodium iron double oxides, Raman spectra for α-NaFeO₂, β-NaFeO₂, Na₄FeO₃, Na₅FeO₄, Na₃FeO₃ has been successfully measured up to 573K. The obtained spectra show the usefulness of Raman spectroscopy as a chemical identification method for these sodium iron double oxides at high temperature up to 573K. (author)