Transferring the high accuracy of the 10 μm CO2 laser bands to far infrared region with internal calibration of CS2

The main aim of the work is to transfer the high accuracy of the CO2 laser bands around 10 μm to far infrared regions around 400 and 250 cm−1 for secondary standards. The bands ν1 + ν2 and 3ν2 of CS2 were measured on the Bruker IFS 120 HR Fourier spectrometer in Oulu with special care and calibrated against CO2. In the second stage the ν2 region around 400 cm−1 was measured at a resolution of 0.001 cm−1. This spectrum was calibrated against 3ν2 internally with the CS2 band system using ladders formed with rotational lines in the bands ν2, 2ν2 − ν2 and 3ν2 − 2ν2. Further, the difference band ν1 − ν2 at 263 cm−1 together with accompanying hot bands was measured on a similar spectrometer in Lund, Sweden, but with a synchrotron radiation source. Using corresponding chains of lines as above this region was calibrated with ν1 + ν2. In this way, problems with conventional calibration could be avoided. Without the effect of the pressure shifts the absolute accuracy of 2.0 × 10−6 and 8.4 × 10−6 cm−1 has been achieved at 400 and 250 cm−1, respectively. Simultaneously the same calibration accuracy is also transferred to residual water lines around the CS2 far infrared bands and the best H2O lines will be given with literature comparisons. In addition to the calibration new results from the observed hot bands of CS2 in the region of the bands ν1 + ν2 and 3ν2 will be given.