Rate constants of electron attachment to alkyl iodides measured by photoionization electron attachment ion mobility spectrometry (PI-EA-IMS)

The photoionization electron attachment ion mobility spectrometry (PI-EA-IMS), with photoelectrons formed by photoionization of organic compound like acetone, has been developed to study electron attachment reactions. With this apparatus, the rate constants for electron attachment to alkyl iodides including ethyl iodide (C 2 H 5 I), 1-propyl iodide (1-C 3 H 7 I), 1-butane iodide (1-C 4 H 9 I) and 2-propyl iodide (2-C 3 H 7 I) have been determined over the average electron energy from 0.29 to 0.96   eV. The rate constants are in the order of magnitude of ∼10 −9   cm 3   molecule −1   s −1 . The experimental measurements show that for straight-chain alkyl iodides, the values of the rate constants follow the order of: k (C 2 H 5 I)   <   k (1-C 3 H 7 I)   ≈   k (1-C 4 H 9 I) which can be explained by the energy threshold for the formation of iodine anion via dissociative electron attachment. For the isomers, 2-C 3 H 7 I has a lower rate constant than 1-C 3 H 7 I which may be caused by the effect of branched chain.