An apparatus for photographing Raman spectra of low-pressure gases at high dispersion is described. A multiple reflection Raman tube, 2 m long, is irradiated by two water-cooled Pyrex mercury arcs operated at 30 amp, and surrounded by a magnesium oxide diffusing screen. A two-prism glass Littrow spectrograph, ƒ/42, gives a reciprocal linear dispersion of 10.5 cm<sup>-1</sup> per mm; its speed is increased fifteen-fold by a cylindrical lens in front of the photographic plate. Rotation-vibrational spectra of gases at 1–3 atmos pressure can be photographed with a resolution of 1 cm<sup>-1</sup>. Various aspects of high-resolution Raman spectroscopy of gases are discussed.
H. L. WELSH, E. J. STANSBURY, J. ROMANKO, and T. FELDMAN, "Raman Spectroscopy of Gases," J. Opt. Soc. Am. 45, 338-343 (1955)