Specular reflectance (SR) and attenuated total reflectance (ATR) infrared (IR) spectroscopy of transparent flat glass surfaces: A case study for soda lime float glass

•We show optical principles of IR spectra for soda lime float glass surface analysis.•We demonstrate the incidence angle dependence of SR-IR spectra.•We present SR-IR spectra of thin and flat glass containing transmission features.•We utilize ATR crystals with different refractive indices to probe hydrous species.

This paper describes the optical principles of specular reflection (SR) and attenuated total reflection (ATR)-infrared (IR) spectroscopy, both of which are useful methods for glass surface analyses. It should be noted that the shape, position, and relative intensity of peaks in reflectance spectra vary drastically depending on the IR incidence angle as well as the probe method (SR vs. ATR). For example, in SR-IR analyses of soda lime glass, the Si–O–Si stretch band shows a blue-shift from its original position and a new peak grows at ~ 1200 cm− 1 as the IR incidence angle increases. In contrast, the Si–O–Si stretch band appears significantly red-shifted from its original position in the ATR-IR spectra of soda lime glass. SR-IR spectra of thin and flat samples can contain transmission spectral features, due to the reflection from the backside, in the region where the bulk absorption coefficient is low. These artifacts are due to the complex nature of refractive index and should not be interpreted as new peaks or new chemical states of soda lime glass surfaces. An ATR-IR analysis to probe hydrous species in glass surface is demonstrated using two ATR crystals with different refractive indices.