Reactions of phenylium ions C6(H,D)5+ with D2

The reaction of phenylium and d-phenylium ions with molecular deuterium has been investigated both experimentally and theoretically. Theoretical calculations have been carried out at the B3LYP/6-31G(*) level of theory. The key features of the potential energy surfaces and all the relevant thermochemical parameters have been calculated. These results are in good agreement with previous theoretical studies concerning the unimolecular dissociation of benzenium ions. Theoretical calculations provide a clear insight on the reaction mechanisms for the system under study. Experimental studies have been carried out by means of a guided beam tandem mass spectrometer. We have measured the reaction cross section for four different reaction channels, as a function of the collision energy, in the range from thermal energies up to about 1 eV. The bimolecular reactivity of C6H5+ is dominated by the substitution of one or two hydrogen atoms by deuterium, leading to the formation of C6H4D+ and C6H3D2+ products. The reaction cross section is nearly the same for the two reaction channels. This fact is interpreted as evidence of a statistical behavior, as expected by assuming a fast shift of hydrogen (deuterium) within the aromatic ring. Another very weak reaction channel leading to the formation of the benzene ion has been measured. The cross section for such a process is lower than about 10(-2) A(2) over the entire energy range explored in our experiment. A structure observed at collision energies around about 0.1 eV has been attributed to the reaction of phenylium ions in their triplet state. When the density of the gas in the scattering cell is increased, the formation of collisionally stabilized benzenium ions is observed. (C) 2003 American Institute of Physics.