The foreign-continuum absorption of water vapour diluted in nitrogen, oxygen and air has been measured in the range of H₂O pure rotational band (50-500 cm^-1). This work is a continuation of our works [1-3], where the self-continuum component was determined in the same region. Spectra recordings were performed at room temperature with a Fourier transform spectrometer associated to a 151-m multipass gas cell located at the AILES beamline of the SOLEIL synchrotron. The HITRAN2016 line list and self-continuum data from [1] were used to extract the foreign-continuum from the experimental spectra. Tests of the baseline stability which is crucial for the continuum determination, were performed. The spectra were recorded for a series of pressure values. The expected linear pressure dependences of the foreign-continuum were checked for all gas mixtures under consideration. Consistency between retrieved H₂O-N₂, H₂O-O₂, and H₂O-air foreign-continuum cross-sections was shown.
The study includes the first laboratory measurements in the wide 90-330 cm^-1 spectral interval. Retrieved foreign-continuum cross-sections are found in good agreement with literature values available in the lower and upper parts of the studied frequency range (see figure). The reported results validate the MT_CKD [4], widely implemented in radiation transfer codes used for the atmosphere and underlying surface remote sensing, even if some overestimation of the MT_CKD values is noted in the centre of the band where experimental data were absent.
This work is partially supported by RFBR project 18-55-16006.

[1] Tatyana Odintsova et al, J Mol Struct, 2020, 1210, 128046.

[2] Tatyana Odintsova et al, J Quant Spectrosc Radiat Transfer, 2019, 227, 190–200.

[3] Tatyana Odintsova et al, J Quant Spectrosc Radiat Transfer, 2017, 187, 116–23.

[4] Eli Mlawer et al, Phil Trans R Soc , 2012, 370, 2520–56.