Transferring the high accuracy of the 10 μm CO 2 laser bands to far infrared region with internal calibration of CS 2

Abstract

The main aim of the work is to transfer the high accuracy of the CO 2 laser bands around 10 μm to far infrared regions around 400 and 250 cm −1 for secondary standards. The bands ν 1 + ν 2 and 3 ν 2 of CS 2 were measured on the Bruker IFS 120 HR Fourier spectrometer in Oulu with special care and calibrated against CO 2. In the second stage the ν 2 region around 400 cm −1 was measured at a resolution of 0.001 cm −1. This spectrum was calibrated against 3 ν 2 internally with the CS 2 band system using ladders formed with rotational lines in the bands ν 2, 2 ν 2 − ν 2 and 3 ν 2 − 2 ν 2. Further, the difference band ν 1 − ν 2 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 ν 1 + ν 2. 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 CS 2 far infrared bands and the best H 2O lines will be given with literature comparisons. In addition to the calibration new results from the observed hot bands of CS 2 in the region of the bands ν 1 + ν 2 and 3 ν 2 will be given.