Transferring calibration from CO2 laser lines to far infrared water lines with the aid of the ν2 band of OCS and the ν2, ν1 − ν2, and ν1 + ν2 bands of 13CS2: Molecular constants of 13CS2

Water (H2O) lines in the far infrared region from 210 to 600 cm−1 have been calibrated against high accurate primary standard of the carbon dioxide (CO2) laser lines with the aid of vibration-rotation transitions in the carbonyl sulfide (OCS) and 13C enriched carbon disulfide (13CS2) molecules. The ν2 band of 13CS2 and the H2O spectrum from 320 to 560 cm−1 was calibrated with the OCS ν2 band, which had earlier been calibrated against the 9.4 μm CO2 laser band that is lying in the same region as the OCS 2ν2 band. The ν1 + ν2 and 3ν2 bands of 13CS2 were measured at the spectral resolution of 0.0032 cm−1. The former band was also calibrated with the 9.4 μm CO2 laser band that is overlapping the 13CS2 band. The calibration was then transferred to the 13CS2ν1 − ν2 difference band at 270 cm−1 and to H2O spectrum in the same region with the 13CS2 fundamental ν2 and associated hot bands and the internal information of the 13CS2 vibration-rotation energy levels. The spectra for far infrared regions were measured at the instrumental resolution of 0.001 cm−1. The range of the ν2 band was measured with a Fourier transform spectrometer in the infrared laboratory at the University of Oulu using a conventional globar source and the lower lying range of the ν1 − ν2 band with a same kind of instrument in the Max laboratory in Sweden by utilizing a synchrotron radiation source. Molecular parameters for 13CS2 were also updated from the analysis of all the available bands.