Site-selective fragmentation in core-excited bromo-chloro-alkanes [Br(CH2) n Cl]

We report strong site-selective ionic fragmentation of the core-excited bromo-chloro-alkanes [Br(CH2)nCl] (n=1,...,3), using time-of-flight mass spectrometry in the multicoincidence mode and monochromatized synchrotron radiation to excite the vicinity of the bromine 3d (65–150 eV) and chlorine 2p edge (150–220 eV), respectively. We observe strong differences between the fragmentation after excitation of the two edges, where for all three molecules the bond between the excited halogen atom and the rest of the molecule is broken preferentially. This site selectivity is discussed in terms of a fast two- and three-body fragmentation which takes place after the primary Auger decay of the core vacancy but on the same time scale as further autoionization.