This thesis studies the formation mechanisms and the composition of Titan's aerosols analogs, so called tholins. The study of the gas phase allowed identifying several aerosols precursors, especially nitrogen-bearing species such as imines and nitriles. These species may be a first step on the gas to solid transition. The study of the infrared absorbance properties of tholins allowed providing for the first time the wavelength dependence of their linear absorption coefficient from far- to mid-infrared. The investigation on tholins chemical composition allowed to infer their polymeric structure and to detect a large amount of nitrogen in this structure. The last part of the thesis is dedicated to a comparison of the tholins chemistry induced by different energy sources. On a general way, this thesis proposes, when possible, the comparison between data obtained in the lab and actual observations of Titan's atmosphere.
