New experimental measurements of the Collision Induced Absorptions of H2-H2 and H2-He in the 3600-5500 cm−1 spectral range from 120 to 500 K

Abstract

The Collision-Induced Absorption (CIA) fundamental band of H₂ has been studied in the 3600–5500 cm⁻¹ spectral range for temperatures ranging from 120 to 500 K for both a pure H₂ gas and a H₂-He mixture. We used a simulation chamber called PASSxS (Planetary Atmosphere System Simulation x Spectroscopy) developed at INAF/ISAC which contains a Multi-Pass cell interfaced with a Fourier Spectrometer, aligned to reach an optical path of 3.28 m. The H₂-H₂ and H₂-He binary absorption coefficients (BACs) have been derived for seven temperatures in the chosen range and provided in tabular form, including the unexplored high-temperature range above 300 K. We also calculated the integral of the H₂-H₂ and H₂-He experimental BACs in the reduced 4000–5000 cm⁻¹ spectral range, finding a linear trend with temperature in both cases. The integrals have also been computed with larger uncertainties for the whole band, in the total 3600–5500 cm⁻¹ spectral range including the band's wings, partially affected by the water vapor absorption. The integrals calculated over the whole and reduced spectral ranges are collected in tables. In addition, we performed measurements with a H₂-He mix for different mixing ratios to explore possible deviations from the linear combination of the BACs. The experimental BACs have been shown in comparison with Abel and Borysow's ab initio models for a temperature of about 400 K, resulting in a good agreement over almost the whole spectral range, with a maximum deviation around the main peak of the band. Data and models also show a good agreement in the linear trend of the integrated BACs with temperature, apart from the H₂-H₂ Borysow's BACs, which follow a quadratic trend. Finally, we resolved all the interference dips, which were not taken into account by the existing theoretical models.