Optical properties of energetic materials from infrared spectroscopy

A method of determining infrared (2.5-18 μm) optical properties of dielectric, crystalline, particulate solids such as energetic materials was developed based on KBr-FTIR (infrared) spectroscopy. Two techniques (spectral subtraction and baseline shifting) were used to account for light scattering by the KBr matrix. An independent CO₂ laser-spatial filtering measurement was also developed to check the spectral subtraction approach. The method is demonstrated here for the oxidizer ammonium perchlorate (AP). The Rayleigh-Gans limit of light scattering theory was exploited to establish a relationship between the apparent KBr-pellet absorption coefficient and the intrinsic AP absorption coefficient. Dispersion theory was used to determine refractive index from the absorption index for AP. Conventional (nonscattering) FTIR spectroscopy was also used to determine the absorption coefficient for the common solid propellant binder hydroxyl-terminated polybutadiene.