LOW-PRESSURE GAS-PHASE REACTIONS OF THE ATOMIC OXYGEN RADICAL-ANION WITH HALOMETHANES STUDIED USING FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE

The gas-phase reactions of the 0(-.) radical anion with the halomethan es CH(3)X, CH(2)X(2), CHX(3), CX(4), CF(3)X, CF(2)X(2), CFX(3) (X = Br and Cl) and CXClBr(2) (X = Cl and F) have been examined at a low pres sure (10(-5)-10(-4) Pa) with use of Fourier transform ion cyclotron re sonance (FTICR) mass spectrometry, The overall reactions proceed essen tially with the collision rate and lead to a variety of product ions d ependent on the number and nature of the halogen atoms present in the substrate. For CH3Cl and CH3Br, the dominant pathways are H-. abstract ion, H-2(+.) abstraction and nucleophilic substitution. With CH2Cl2, p roton transfer is an additional major pathway and in the reaction with CH2Br2 attack on a halogen atom with formation of BrO- ions also occu rs. In the reactions with CHCl3 and CHBr3, proton transfer competes wi th attack on a halogen atom, whereas initial attack on a halogen atom dominates in the reactions of O--. with the CCl4 and CBr4 methanes. At tack on the carbon atom is the main process if CF3Cl is the substrate and results in F-, Cl- as well as FCl-. ions. For CF3Br, however, atta ck on the bromine atom with formation of BrO- ions dominates over the reaction at the carbon atom. In the reactions with CF2Cl2, CFCl3, CF2B r2 and CFBr3 as well as the CCl2Br2 and CFClBr2 methanes, most product ions are formed by competing attack on a chlorine and bromine atom. F or some of the halomethanes, the present findings are compared with re ported results obtained with use of the high pressure (approximate to 70 PA) flowing afterglow and selected ion how tube methods. (C) 1997 b y John Wiley & Sons, Ltd.