Modifications affecting the resolution and frequency calibration capability of the Beckman IR-9 infrared spectrophotometer are described and discussed. Under favorable conditions these modifications enable the instrument to be calibrated with an absolute accuracy of 0.03 cm<sup>−1</sup> or better; resolution is also improved so that spectral slitwidths may be reduced by approximately √2 over normal specifications. These results are illustrated with vibration-rotation spectra from NH<sub>3</sub>, CH<sub>4</sub>, and HBr.
R. M. Kirk and P. M. Wilt, "Resolution and Frequency Calibration Performance of Beckman IR-9 Infrared Spectrophotometer," Appl. Spectrosc. 28, 536-540 (1974)