Diffuse reflection spectroscopy is a very sensitive method for detecting changes at the surfaces of rough materials. It is particularly effective for powders that have high surface areas. This makes diffuse reflectance invaluable for studies of heterogeneous catalysis, gas-solid interactions, photochemical reactions, and oxidation mechanisms. This Low Temperature Reaction Chamber is well suited for performing such studies under carefully variable temperatures and pressures. These Low Temperature Reaction Chamber allow diffuse reflection measurements under a wide range of controlled temperatures and pressures and are used in conjunction with the Praying Mantis Accessory for FT-IR and UV-Vis diffuse reflectance spectroscopy.