Combination of absorbance with reflectance

In Section 4.4.1.2 regular reflectance has been announced as a method to follow photoreactions taking place in solid material. Since reflectance at interfaces depends on the refractive indices of matter at both sides of this interface, the signal measured either in transmittance or reflectance depends 

Photokinetic constants for the photoreaction of l-hydroxy-benzotriazole, which forms nitro-sobenzene, p-nitrophenoi, and nitrobenzene 

The change in the interference spectrum can be used to monitor photochemical processes taking place in solid matter, which influence the complex refractive index 

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