Unusual temperature dependence in dissociative electron attachment to 1,4-chlorobromobenzene

Electron attachment to 1,4-chlorobromobenzene yields the ionic fragments Cl - and Br- appearing in the energy range approximate to0-1 eV with Br by abo ut a factor of 70 more intense at room temperature. Increasing the temperat ure of the target molecule up to 540 K results in an unexpected temperature dependence of the cross-section in that it first increases and after passi ng a maximum (400 K for Br- and 460 K for Cl-) decreases. This behaviour is qualitatively interpreted by the temperature dependent population of the r elevant normal modes containing the C-Cl and C-Br stretch vibration. (C) 20 01 Elsevier Science B.V. All rights reserved.