Abstract

By use of the ν2 and 2ν2 bands of carbonyl sulfide (OCS), the high accuracy of the CO2 laser lines is transferred from 10 µm to the far-infrared region near 20 µm. Measurements were performed with a slightly modified Bruker IFS 120 HR spectrometer at the infrared laboratory of the University of Oulu. The effect of the pressure shift was reduced by measurement of the 2ν2 band with the CO2 laser band in a long-path cell with low sample pressures. With highly sensitive measurement, the absolute accuracy of the 2ν2 band center was reduced to 1.4×10-6 cm-1. Together with the accurate result for the 2ν2 band, measurement of the ν2 band with a resolution of 0.001 cm-1 and a signal-to-noise ratio of ∼150, accurate wave numbers in the region of the lower band can also be obtained. To the best of the author’s knowledge, the absolute accuracy of 3.9×10-6 cm-1 for the ν2 band center is the best ever reached in the region near 500 cm-1. New accurate wave number tables are presented for the bands 02000000 near 1047 cm-1 and 02000110 and 01100000 in the region from 495 to 555 cm-1. The most important factors that limit the performance of Fourier spectrometers in high-absolute-accuracy measurements are discussed. With systematic alignment methods these barriers have been overcome with the spectrometer used. An easy method to confirm the quality of a measured spectrum is presented.

© 2004 Optical Society of America

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