Electron attachment to aliphatic hydrocarbons of the form n-C _NH_2N+1Br(N =2-6 and 8) II. A Swarm-beam study

A swarm-beam study has been made of brominated hydrocarbons of the form n-C_NH_2N+1Br(N = 2-6 and 8). At energies below ∼3 eV the abundant ion found in the beam study was Br~. The dissociative attachment cross section σ-da(∑) peaked at 0.76, 0.74, 0.73, 0.70, 0.71, and 0.13 eV, and had peak values equal to 3.95, 4.14, 5.50, 6.13, 7.41, and 32.2X10 ^-18 cm² for N = 2-6 and 8, respectively. A small decrease has been observed in the cross-section width with increasing reduced mass M, of the R( = n-CwH₂ molecules. This and the increase in a-4 with M, are discussed within the resonance-scattering-theory treatment of dissociative electron attachment to diatomic molecules. For some of the molecules studied, potential energy diagrams for RBr and RBr ^* and separation and autoionization lifetimes for RBr ^* are given.