Fluorinated methyl cation (CF3+, CFH2+)-alkyl nitrile cluster ions

Ion-molecule reactions of CF3+ or CFH2+ with an acetonitrile-butyronitrile mixture yield product cluster ions in which the two neutral molecules are a ssociated with the cation, The structures of the ion-molecule product ions were investigated by collision-induced dissociation in a multi-quadrupole m ass spectrometer, The cluster ions fragment by loss of one neutral alkyl ni trile, The abundance of the fragment ions shows an unexpected inverse corre lation with the proton affinity of the alkyl nitrile, This result is incons istent with the formation of a simple cation-bound dimeric cluster containi ng two alkyl nitrile molecules and a fluorinated methyl cation; instead, a pair of non-symmetrical dimeric complexes, separated by a large internal ba rrier, is indicated. This result is analogous to that observed for the puta tive methyl cation-bound heterodimer of acetonitrile and butyronitrile, Col lision energy dependence studies and ab initio calculations suggest that th e dimeric complexes are formed in potential energy wells located in an appr oximately symmetrical potential energy surface. Quasiequilibrium theory cal culations were used in order to obtain additional insights into the experim ental data. Copyright (C) 2000 John Wiley & Sons, Ltd.