Low Pressure Gas-phase Reactions of the Atomic Oxygen Radical Anion with Halomethanes Studied Using Fourier Transform Ion Cyclotron Resonance
✍ Scribed by P. O. Staneke; J. Kauw; M. Born; S. Ingemann; N. M. M. Nibbering
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 129 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0951-4198
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✦ Synopsis
The gas-phase reactions of the O -• radical anion with the halomethanes 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 pressure (10 -5 -10 -4 Pa) with use of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The overall reactions proceed essentially with the collision rate and lead to a variety of product ions dependent on the number and nature of the halogen atoms present in the substrate. For CH 3 Cl and CH 3 Br, the dominant pathways are H . abstraction, H 2 + • abstraction and nucleophilic substitution. With CH 2 Cl 2 , proton transfer is an additional major pathway and in the reaction with CH 2 Br 2 attack on a halogen atom with formation of BrO -ions also occurs. In the reactions with CHCl 3 and CHBr 3 , proton transfer competes with attack on a halogen atom, whereas initial attack on a halogen atom dominates in the reactions of O -• with the CCl 4 and CBr 4 methanes. Attack on the carbon atom is the main process if CF 3 Cl is the substrate and results in F -, Cl -as well as FCl -• ions. For CF 3 Br, however, attack on the bromine atom with formation of BrO -ions dominates over the reaction at the carbon atom. In the reactions with CF 2 Cl 2 , CFCl 3 , CF 2 Br 2 and CFBr 3 as well as the CCl 2 Br 2 and CFClBr 2 methanes, most product ions are formed by competing attack on a chlorine and bromine atom. For some of the halomethanes, the present findings are compared with reported results obtained with use of the high pressure (Ϸ 70 PA) flowing afterglow and selected ion flow tube methods.