Selected ion flow tube studies of the reactions of H 3O +, NO +, and O 2+ with eleven amine structural isomers of c 5h 13n

Abstract

We describe the results of a selected ion flow tube (SIFT) study of the reactions of H 3O +, 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 = C 5H 13N. These isomers comprise seven primary, two secondary, and two tertiary amines. The product of the reactions of H 3O + with the primary amines progress from only the parent protonated molecule MH + for the linear chain 1-pentylamine towards an increasing fraction of NH 4 + as the carbon chain becomes more branched, until for the very branched 2-methyl-2-butylamine reaction, NH 4 + is the major product (>90%). For the secondary and tertiary amine reactions with H 3O + 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 M + 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 (= CH 3, C 2H 5, C 3H 7). 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.