High-resolution infrared spectroscopy with a small grating instrument has now been extended to wavelengths of nearly 200 microns. In the range 5-50 microns the achieved resolution was about 0.3 cm<sup>-1</sup> or slightly better. Beyond 50 microns the resolution varied from 0.5 to 1.0 cm<sup>-1</sup>. No predispersive device was used, but filters, residual-ray reflections, selective chopping of radiation, and "off-blaze" use of the doubly passed gratings were employed to remove higher orders from the spectra. These devices are discussed briefly and their characteristics for the various spectral regions have been tabulated. Calibration has been carried out with higher orders of atomic emission lines and absorption lines of previously measured molecular spectra. Wave-number precision is estimated as about 0.04-0.05 cm<sup>-1</sup> in most spectral regions. Performance of the spectrometers is illustrated by reproductions of the actual recorded spectra of water vapor at 1600, 300, and 200-55 cm<sup>-1</sup>, of ethylene and ammonia at 950 cm<sup>-1</sup>, of benzene at 673 cm<sup>-1</sup>, and of carbon disulfide at 400 cm<sup>-1</sup>.
R. C. LORD and T. K. MCCUBBIN, JR., "Infrared Spectroscopy from 5 to 200 Microns with a Small Grating Spectrometer," J. Opt. Soc. Am. 47, 689-697 (1957)