Activation of hydrogen and methane by thermalized FeO+ in the gas phase as studied by multiple mass spectrometric techniques

Abstract

The ion-molecule reactions of thermalized iron-oxide cation FeO+ with dihydrogen and methane have been studied by three different experimental techniques: Fourier transform ion cyclotron resonance (ICR), guided ion beam (GIB), and selected-ion flow tube (SIFT) mass spectrometry. Although these studies agree in a qualitative sense, i.e., FeO+ brings about activation of H2 and CH4 with quite low efficiencies, there exists a considerable quantitative divergence as far as rate constants and branching ratios are concerned. The sources of error in these three related, but yet different experimental techniques are analyzed and critically reviewed. This error analysis brings the data to internal consistency with each other, once an accurate reference is used for calibration. In general, the rate constants obtained with the SIFT apparatus appear as the most accurate ones, while those obtained under ICR conditions are slightly too large, and the rate constants determined with the GIB instrument are somewhat lower than SIFT. However, the branching ratios for the formation of Fe+ and FeOH+ in the reaction of FeO+ with methane are subject to more subtle effects. In the SIFT apparatus, termolecular stabilization of the intermediates causes differences from the ICR and GIB measurements, which were obtained under single-collision conditions. © 1997 Elsevier Science B.V.