Standard Reference Materials SRMs 2241 through 2243 are certified spectroscopic standards intended for the correction of the relative intensity of Raman spectra obtained with instruments employing laser excitation wavelengths of 785 nm, 532 nm, or 488 nm/514.5 nm. These SRMs each consist of an optical glass that emits a broadband luminescence spectrum when illuminated with the Raman excitation laser. The shape of the luminescence spectrum is described by a polynomial expression that relates the relative spectral intensity to the Raman shift with units in wavenumber (cm(-1)). This polynomial, together with a measurement of the luminescence spectrum of the standard, can be used to determine the spectral intensity-response correction, which is unique to each Raman system. The resulting instrument intensity-response correction may then be used to obtain Raman spectra that are corrected for a number of, but not all, instrument-dependent artifacts. Peak area ratios of the intensity-corrected Raman spectrum of cyclohexane are presented as an example of a methodology to validate the spectral intensity calibration process and to illustrate variations that can occur in this measurement.

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In situ Raman spectroscopy was employed to investigate iron corrosion in air saturated water at a pressure of 25.1 MPa and temperatures from 21 to 537ЊC. Upon heating, various combinations of Fe 3 O 4 , ␣-Fe 2 O 3 , ␥-FeOOH, and ␥-Fe 2 O 3 were observed depending on the location on or temperature of the iron coupon. In some cases, different species were observed at the same temperature at different locations on the surface. This was attributed to oxygen concentration gradients in the solution caused by recirculation zones in the cell. The surface of the corrosion coupon changed little after it was heated to 537ЊC. This was attributed to the formation of a relatively thick, protective oxide scale after exposure to supercritical water. The ex situ Raman spectra were very similar to the in situ spectra obtained during cooling but different from those obtained during heating. This indicates that the corrosion layer present during cooling is similar to that observed ex situ but different from that observed during heating. Ex situ characterization of the coupon identified a two layered structure: an inner corrosion layer consisting of Fe 3 O 4 and ␣-Fe 2 O 3 and an outer layer consisting of ␥-Fe 2 O 3 and ␣-Fe 2 O 3 .

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