Selected ion flow tube studies of the reactions of H3O+, NO+, and O2+ with eleven amine structural isomers of C5H13N

We describe the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+, and O-2(+), which are the chosen ions for chemical ionisation in our SIFT trace gas analytical method, with eleven structural amine isomers having the molecular formula M = C5H13N. These isomers comprise seven primary, two secondary, and two tertiary amines. The product of the reactions of H3O+ with the primary amines progress from only the parent protonated molecule MH+ for the linear chain 1-pentylamine towards an increasing fraction of NH4+ as the carbon chain becomes more branched, until for the very branched 2-methyl-2-butylamine reaction, NH4+ is the major product (>90%). For the secondary and tertiary amine reactions with H3O+ the major product ion is MH+ in parallel with product ions (M-H)(+) that result from H-2 elimination from MH+, the latter ions being 30% of the product distribution for the tertiary amine, N,N-diethylmethylamine reaction. The NO+ reactions with the primary amines mostly proceed via parallel nondissociative charge transfer (producing Mi ions) and hydride ion transfer [producing (M-H)(+) ions]. With increased branching of the primary amines and for the secondary and tertiary amines, dissociative charge transfer occurs, mainly producing (M-R)(+) ions and various alkyl radicals, R (= CH3, C2H5, C3H7). The O-2(+) reactions with all these amine isomers proceed via dissociative charge transfer, mainly producing (M-R)(+) ions. Comparisons of the products of these O-2(+) reactions with the "cracking patterns" produced by 70 eV electron impact on these amines show remarkable similarities except for one or two of the isomers. (Int J Mass Spectrom 185/186/187 (1999) 139-147) (C) 1999 Elsevier Science B.V.