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J Chem Phys. 2014 Feb 14;140(6):064302. doi: 10.1063/1.4864205.

Line broadening of confined CO gas: from molecule-wall to molecule-molecule collisions with pressure.

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Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS (UMR 7583), Universités Paris-Est Créteil et Paris Diderot, Institut Pierre-Simon Laplace, Université Paris-Est Créteil, 94010 Créteil Cedex, France.
Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS (UMR 8214), Université Paris-Sud, Bât. 350, Orsay F-91405, France.
Service de Chimie Quantique et Photophysique, C.P. 160/09, Université Libre de Bruxelles, 50 avenue F.D. Roosevelt, B-1050 Brussels, Belgium.
Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM), CNRS (UMR 8523), CERLA/IRCICA, Université de Lille 1, UFR de Physique Bât. P5, 59655 Villeneuve d'Ascq Cedex, France.


The infrared absorption in the fundamental band of CO gas confined in porous silica xerogel has been recorded at room temperature for pressures between about 5 and 920 hPa using a high resolution Fourier transform spectrometer. The widths of individual lines are determined from fits of measured spectra and compared with ab initio predictions obtained from requantized classical molecular dynamics simulations. Good agreement is obtained from the low pressure regime where the line shapes are governed by molecule-wall collisions to high pressures where the influence of molecule-molecule interactions dominates. These results, together with those obtained with a simple analytical model, indicate that both mechanisms contribute in a practically additive way to the observed linewidths. They also confirm that a single collision of a molecule with a wall changes its rotational state. These results are of interest for the determination of some characteristics of the opened porosity of porous materials through optical soundings.


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