Le sujet de cette thèse est principalement ciblé sur l’étude du transport ionique dans les sulfates d’alcalins de la famille LIMSO₄, où M=Na, K, Rb, Cs. Une attention particulière est portée sur l’étude du système LiNaSO₄, le plus intéressant en termes de dynamique ionique, par RMN en fonction de la température. Dans le cadre de cette étude, nous avons effectué des mesures de temps de relaxation et de largeurs de raie pour toute la série de composés. Des mesures de coefficients d’autodiffusion du ₇li et du ²³Na, ont été menées depuis l’ambiante jusqu’à la température de fusion. Pour la première fois, nous avons pu mesurer la cinétique de transition de phase dans LiNaSO₄, à partir d’une nouvelle méthode basée sur la différence de temps de relaxation dans les deux phases de part et d’autre d e la transition, mais sans mesurer forcément le T₁. Cette technique élaborée dans le cadre de ce travail permet de mesurer l’évolution au cours du temps du volume de la phase qui apparait pour des vitesses de refroidissement contrôlées. Nous avons aussi mené une étude par RMN des réorientations des groupements sulfates dans la phase basse température. L’influence des réorientations des SO ₄² sur les couplages quadripolaires au noyau 7li, a été étudiée par un modèle de réorientation par sauts, qui n’avait encore jamais été utilisé pour les sulfates. La méthode proposée est une méthode à « bas couts » car elle permet d’atteindre l’information sur la dynamique des groupements sulfates sans enrichir l’échantillon en ¹⁷O ou de mener des expériences très longues pour le ³³S, ou sans passer par les mesures de temps de relaxation. Afin d’analyser le rétrécissement par le mouvement (motional narrowing) en fonction de la température dans les solides avec deux sous réseaux cationiques diffusant comme dans le cas du LiNaSO₄ , nous avons élaboré un modèle permettant de fitter l’évolution observée à deux marches de la largeur de raie RMN avec la température. La fonction analytique obtenue a été étendue au cas de distributions de temps de corrélation. / The main goal of a present research is a detailed study of ionic transfer in double sulfates belonging to the LIMSO₄ family, where M = Na, K, Rb, Cs. The most attention has been paid to LiNaSO₄ as to the most interesting (in terms of the ion dynamics) compound among other double sulfates. We have carried out magnetic relaxation measurements and line width analysis for all compounds under consideration. Moreover, PGF NMR measurements of ₇li and ²³Na self-diffusion coefficients in LiNaSO4 have been carried out. For the first time, we have measured the phase transition kinetics in LiNaSO₄. For this purpose, we developed a new technique, which is based on the difference of spin-lattice relaxation times in the two phases, but which does not involve the direct measurement of T₁. Elaborated technique allows measuring time evolution of the volume of the appearing phase at controlled cooling rates. We have carried out NMR study of the sulfate ion reorientations in the low-temperature modification of LiNaSO₄. The influence of the SO ₄² reorientational jumps on the quadrupolar interactions of 7Li nuclei was investigated b y a j ump reorientational model, which has not previously been app lied to sulfates. The proposed method is a “low-cost” technique, since it does not require an ¹⁷O enriched sample and dispenses with time-consuming ³³S NMR. Other advantage of a given method is a possibility to probe reorientational motions without NMR relaxation measurements. To analyze motional narrowing in solids with two diffusing spin sublattices (such case occurs, e.g., in LiNaSO₄) we deduced a formula, which can be used for fitting of the two-step temperature dependencies of the NMR line width. The obtained function has been al so ex tended to the case, when a distribution of correlation times takes place. The advantage of this approach is that even in the case of distribution of correlation times, the fitting function could be expressed in the analytical form.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere. / Science, Faculty of / Chemistry, Department of / Graduate