This thesis presents the results of research work of combustion and astrophysical interest. The results, using a combination of sophisticated methods, concern the gas phase reactions of small molecules at extreme temperatures and the photophysics of carbon nanoparticles. The rate coefficients of reactions at high temperature (300-1116K) between cyanide radical CN with two hydrocarbons (C₂H₄ and C₂H₆) were measured using a novel prototype for the study of high temperature reaction in the gas phase: the high temperature reactor coupled to PLP-LIF technique (Pulsed Laser Photolysis-Laser Induced Fluorescence). These reactions were shown to be fast and diplay an energy barrier. The prerequisite for the study of reaction kinetics is the determination of the rotational temperature of the flow by spectroscopy of the CN radical and also the study of its vibrational relaxation by means of semi-empirical calculations. In a second experiment, we were interested in the reaction of electron attachment at low temperature (39-170K) on the POCl₃ molecule by means of the CRESU (French acronym for Cinétique de réaction en Ecoulement Supersonique Uniforme) technique. The electron attachment coefficient of this reaction was determined showing a weak dependence on gas temperature. It also showed the reversal of the output channels, the dissociative and non dissociative one, at around 170K involving two major products. The last part of the thesis presents our research perspective to study the photophysics of carbon nanoparticles produced by combustion. We implemented a system that produces soot nanoparticles using a burner. The experiment involved probing the interaction of soot nanoparticles with soft X-rays (1eV-1keV) and we studied this interaction using photoelectron detection and time of flight mass spectrometry.
