Etude spectroscopique de mélanges à base d’acétylène

: expérience et modélisation

Abstract

This work is devoted to the study of gaseous mixtures based on acetylene diluted in other gases. Two complementary aspects are developed: an experimental study of the spectral parameters of infrared absorption lines and a theoretical study which is able to model the intermolecular collisions. The experimental part concerns the study of the temperature dependence of the collisional broadening and shift coefficients of infrared absorption lines of self-perturbed acetylene and diluted in hydrogen, nitrogen or xenon. These measurements are carried out by diode-laser spectroscopy at very high resolution, for absorption lines in the n4+n5 ro-vibrational band, located around 1330 cm−1, and under conditions of very different pressures (between 20 mbar and 400 mbar) and temperatures (between 170.0 K and 500.0 K). The determinations of the collisional broadening widths and shifts are obtained by fitting to the experimental profiles the theoretical lineshapes (Voigt, Rautian-Sobel’Man and Galatry). The temperature dependencies of the collisional shift coefficients of lines of self-, N2- or Xe-perturbed C2H2 are analyzed for the first time in the n4+n5 ro-vibrational band. The measurement of these coefficients has required the development of an experimental technique allowing to have a great accuracy. The theoretical part is devoted to the modeling of interactions between surrounding molecules. The intermolecular collisions are described by a semiclassical model developed by Robert and Bonamy. The latter considers that the molecule energy levels are quantified but supposes that their trajectories are governed by the classical mechanics laws. An ab initio potential is implemented within the numerical version of this model developed few years ago. Indeed, the description of the intermolecular interaction potential is very important because of its effect on the molecular collisions and, in addition, its isotropic part has a great influence on the molecules trajectories. Taking into account an ab initio potential, one avoids some approximations and it’s especially an honest way to test the semiclassical model. Two molecular systems are concerned by these calculations : N2-H2 and C2H2-H2. Finally, these two aspects bring different but complementary informations. In one way, a numerical simulation has to be corroborated by exprimental results in order to validate its results. In an other way, an experimental setup is always limited by its technical characteristics and thus, the modeling allows to explore conditions which are very difficult to access by experiments.

Date of Award	11 Sept 2012
Original language	French
Awarding Institution	University of Namur
Sponsors	Université de Franche-Comté
Supervisor	Muriel Lepere (Supervisor), Joël Bonamy (Jury), Marie-Renée DE BACKER - BARILLY (Jury), Pierre Defrance (Jury), Pierre Joubert (Co-Supervisor), Ghislain Blanquet (Jury) & Bertrand Hespel (President)