Far infrared measurements of absorptions by CH4+CO2 and H2+CO2 mixtures and implications for greenhouse warming on early Mars
Martin Turbet, Ha Tran, Olivier Pirali, Francois Forget, Christian Boulet, Jean-Michel Hartmann
(Submitted on 7 May 2018)
We present an experimental study of the absorption, between 40 and 640 cm$^{-1}$, by CO$_2$, CH$_4$ and H$_2$ gases as well as by H$_2$+CO$_2$ and CH$_4$+CO$_2$ mixtures at room temperature. A Fourier transform spectrometer associated to a multi-pass cell, whose optics were adjusted to obtain a 152 m pathlength, were used to record transmission spectra at total pressures up to about 0.98 bar. These measurements provide information concerning the collision-induced absorption (CIA) bands as well as about the wing of the CO$_2$ 15 $\mu$m band. Our results for the CIAs of pure gases are, within uncertainties, in agreement with previous determinations, validating our experimental and data analysis procedures. We then consider the CIAs by H$_2$+CO$_2$ and CH$_4$+CO$_2$ and the low frequency wing of the pure CO$_2$ 15 $\mu$m band, for which there are, to our knowledge, no previous measurements. We confirm experimentally the theoretical prediction of Wordsworth et al. 2017 that the H$_2$+CO$_2$ and CH$_4$+CO$_2$ CIAs are significantly stronger in the 50-550 cm$^{-1}$ region than those of H$_2$+N$_2$ and CH$_4$+N$_2$, respectively. However, we find that the shape and the strength of these recorded CIAs differ from the aforementioned predictions. For the pure CO$_2$ line-wings, we show that both the $\chi$-factor deduced from measurements near 4 $\mu$m and a line-mixing model very well describe the observed strongly sub-Lorentzian behavior in the 500-600 cm$^{-1}$ region. These experimental results open renewed perspectives for studies of the past climate of Mars and extrasolar analogues.
Comments: Submitted to Icarus. 22 pages, 7 figures, 2 tables. Comments are welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atomic and Molecular Clusters (physics.atm-clus); Chemical Physics (physics.chem-ph)
Cite as: arXiv:1805.02595 [astro-ph.EP] (or arXiv:1805.02595v1 [astro-ph.EP] for this version)
Submission history
From: Martin Turbet [view email]
[v1] Mon, 7 May 2018 16:12:12 GMT (1932kb)
https://arxiv.org/abs/1805.02595
