Elementary Processes in the Gas-Phase Photodecomposition of Singlet and Triplet 3-Chloro-3-methyldiazirine

Article abstract of DOI:10.1021/j100271a035

3-Chloro-3-methyldiazirine has been photolyzed in the gas phase at 416, 365, and 337 nm.With these wavelengths, ³n?^* and ¹n?^* states could be prepared, the last one with different amounts of rovibrational energy.The elementary processes occurring after the optical excitation have been analyzed with the help of algorithms recently devloped.The triplet leads to "hot" vinyl chloride through the intermediacy af a diradical.In the case of the singlet, two competitive pathways take place.The first one switches to the triplet route after the initial excited diazirine undergoes an intersystem crossing process.The second one produces the "hot" vinyl chloride through adiabatic isomerization of the diazirine to the isomeric diazo compound.In both routes, the intermediate diradical and diazo compound decompose to singlet chloromethylcarbenes differing only in their rotovibrational energy content.Subsequent 1,2-hydrogen shift gives rise to the final vinyl chlorides containing different amounts of internal energy.The reaction mechanism put forward agrees with all the data known to date about this photodecomposition.We should emphasize that the purpose of this work was the study of the unimolecular processes occuring in the photodissociation.Minor subsequent or parallel bimolecular reactions possibly occurring (formation of dichloroethanes, for example) have been purposely excluded.However, some quenching experiments have been used as probes of the reaction mechanism.