Étude des spectres de rotation pure de molécules organiques complexes radicalaires

High-resolution spectroscopy of dehydrogenated complex organic molecules (COMs) is essential to better understand chemical processes in combustion, atmospheric chemistry, and astrochemistry, and to deepen our knowledge in the field of molecular physics. However, the high reactivity and instability of these large radicals make their production and spectroscopic detection particularly challenging in the laboratory.This thesis focuses on the study of the rotational spectrum, in the (sub-)millimeter range, of several dehydrogenated COMs for which no rotational data are available in the literature. The radicals were generated by hydrogen abstraction from a precursor molecule via collision with fluorine atoms and then detected using a frequency-multiplication chain spectrometer. Two selective modulation techniques for paramagnetic species, enabling the recording of broadband radical spectra, were implemented: Zeeman modulation and Faraday rotation modulation, the latter offering higher sensitivity and resolution.The spectra of the vinoxy (CH₂CHO), vinyloxy (CH₂OCHO), acetonyl (CH₃COCH₂), methoxy methyl (CH₃OCH₂), methoxy carbonyl (CH₃OCO), and hydroxy vinoxy (CHOCHOH) radicals were recorded, and their analysis is presented.The results provide crucial reference data for the detection of these large radicals in various environments, as well as for the study of fine molecular couplings in these species. The experimental methodology developed and presented in this thesis is directly applicable to the study of other complex organic radicals.