Wavelength calibration of a dispersive near-infrared spectrometer using trichloromethane as a calibration standard

Since differences in wavelength calibration between instruments are arguabl y a primary source of error encountered in the transfer of calibration mode ls from one instrument to another in near-infrared (NIR) spectroscopy, a re adily available, convenient, inexpensive secondary wavelength calibration s tandard for the NIR spectral region is needed. This paper describes the adv antages of trichloromethane as a wavelength standard for the calibration of dispersive NIR spectrometers used in the transmission mode. The spectrum o f trichloromethane, taken with a Fourier transform NIR spectrometer whose w avenumber scale was calibrated with the ro-vibrational lines of ethyne as d etermined by the National Institute of Standards and Technology (NIST), is presented. The wavelengths of four strong, sharp, well-resolved bands of tr ichloromethane were determined with the calibrated Fourier transform NIR sp ectrometer and were found to be 1152.13 +/- 0.01 nm (3 upsilon(1)), 1410.21 +/- 0.01 nm (2 upsilon(1) + upsilon(4)), 1691.9 +/- 0.7 nm (2 upsilon(1)), and 1861.22 +/- 0.01 nm (upsilon(1) + 2 upsilon(4)). These bands w;ere the n used to calibrate the wavelength scale of a commercial 0.25 m monochromat or equipped with a 300 line mm(-1) grating. The calibration revealed that, while the wavelength scale of the monochromator was linear, there was a sys tematic error of about +12 nm in the NIR region.