Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in the far infrared (FIR) has been found to be feasible to ~40 cm−1. High-density polyethylene powder was used as the non-absorbing matrix and diluent. DRIFT spectra in the FIR of compounds representing organic, inorganic, corrdination, glass, catalysts, and others are presented, and are compared with Nujol mull transmission spectra. Other sampling techniques are suggested, including specular (external reflectance–1 pass) reflectance in the FIR.
John R. Ferraro and Kathleen Martin, "Diffuse Reflectance Interferometric Spectroscopy in the Far Infrared Region," Appl. Spectrosc. 38, 270-275 (1984)