Chemical Dynamics of Isolated Carbenes

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We will continue to investigate the photochemistry and photodissociation dynamics of open shell species, in particular carbenes. The focus will be on molecules that are relevant to the chemistry of combustion processes and interstellar space. Due to the high reactivity of open-shell systems we will study them under collision-free conditions in the gas phase. In all experiments we will excite the molecules with laser radiation and deposit sufficient energy to initiate a chemical reaction. The most important detection method employed in the present work is velocity map imaging (VMI) of photofragments, which permits to extract detailed information on the photodissociation dynamics. The following projects will be pursued: We will continue to study the excited state structure and dynamics of the C3H2 isomer propargylene. Furthermore we will start to investigate fulvenallene (C7H6) and fulvenallenyl (C7H5), two species that are so far hardly investigated, but were recently identified to be possible intermediates in soot formation. Another class of compounds of interest to us are relatively stable carbenes, termed "Arduengo"-carbenes. Little is yet known about the excited electronic states of this fascinating class of molecules.Previously we have concentrated on the analysis of H-atoms photofragments. We will now extend our work to the detection of methyl (CH3) fragments and chlorine atoms. Detecting methyl fragments will permit us to study C-C bond breaking in open shell species, a hithereto little investigated pathway. With this method we want to complete our investigation of the alkyl radicals n-propyl and t-butyl. Detection of chlorine atoms permits to illuminate the influence of heavy atoms on the photochemical dynamics of carbenes. We will compare the carbenes c-C3H2 and c-C3HCl to further address this issue.In addition we plan to complement our research program by selected projects with external partners. Ultrafast processes after photoexcitation will be investigated by femtosecond time-resolved photoelectron spectroscopy. Bimolecular reactions of relevance to combustion will be elucidated using IR/UV double resonance spectroscopy. Since a high flux mid-IR source is required, the experiments will be carried out at a free electron laser source.