A selected ion flow tube (SIFT), study of the reactions of H 3O +, NO + and O 2+ ions with a series of alkenes; in support of SIFT-MS

Abstract

We report the results of a detailed selected ion flow tube (SIFT) study at 300 K of the reactions of the 1-alkene and trans-2-alkene isomers of pentene, hexene, heptene, octene and nonene and 1-decene (all liquids at room temperature) with H 3O +, NO + and O 2 +. All 33 reactions proceeded at the collisional rate under these SIFT conditions (helium carrier gas pressure of 0.7 Torr). The H 3O + reactions with both isomers of each alkene proceeded via exothermic proton transfer, which resulted in partial dissociation of the MH + product ions for the longer chain alkene molecules, M, the number of fragment ions depending on the chain length. However, the mechanisms of the NO + reactions were isomer specific, those involving the 1-alkenes proceeded via NO +·M production (three-body association) followed by partial stabilisation and partial dissociation of the nascent adduct ion to several products, including ions of the kind RHNO + (R=CH 3, C 3H 5, C 4H 7, etc.), whilst those involving the trans-2-alkene isomers proceeded partially via charge (electron) transfer to give M + parent ions and via hydride ion (H −) transfer giving (MH) + ions. The O 2 + reactions all proceeded via charge transfer to give M + ions together with multiple fragment ions. These O 2 + SIFT data are compared and contrasted with the corresponding electron ionisation spectra (from the NIST database) for these alkenes.