The foreign-continuum absorption of water vapour in the far-infrared (50-500 cm$^{-1}$)

Abstract

We investigated the continuum absorption of water vapour diluted in nitrogen, oxygen and air in the range of the pure rotational band of the water molecule (50-500 cm^-1). 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 SOLEIL synchrotron facility. The study includes the first laboratory measurements in the wide 90-330 cm^-1 interval. Tests of the baseline stability, crucial for the continuum determination, are reported together with the expected pressure dependences of the continuum absorption, measured over different pressure ramps. 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. The reported results validate the MT_CKD foreign-continuum empirical model, widely used in atmospheric applications, even if some overestimation of the MT_CKD values is noted in the centre of the band where experimental data were absent.

Olivier Pirali

Director of Research

My research interests includes high resolution molecular spectroscopy, laboratory astrophysics, and THz generation.