Photofragmentation spectra of halogenated methanes in the VUV photon energy range

In this paper an investigation of the photofragmentation of dihalomethanes CH2X2 (X = F, Cl, Br, I) and chlorinated methanes (CHnCl4-n with n = 0-3) with VUV helium, neon, and argon discharge lamps is reported and the role played by the different halogen atoms is discussed. Halogenated methanes are a class of molecules used in several fields of chemistry and the study of their physical and chemical proprieties is of fundamental interest. In particular their photodissociation and photoionization are of great importance since the decomposition of these compounds in the atmosphere strongly affects the environment. The results of the present work show that the halogen-loss is the predominant fragmentation channel for these molecules in the VUV photon energy range and confirm their role as reservoir of chlorine, bromine, and iodine atoms in the atmosphere. Moreover, the results highlight the peculiar feature of CH2F2 as a source of both fluorine and hydrogen atoms and the characteristic formation of I-2(+) and CH2+ ions from the photofragmentation of the CH2I2 molecule.