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Crossed-beam study of Co+(3F4)+propane: experiment and density functional theory
Yi1, Reichert, Holthausen
1Department of Chemistry, University of Wisconsin-Madison, 53706-1396, USA.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|August 5, 2000
Summary
Cobalt ion reactions with propane show distinct product pathways. Density functional theory calculations explain the observed branching ratios, favoring H2 elimination over CH4 for Co+ ions.
Area of Science:
- Chemical Dynamics
- Computational Chemistry
- Surface Science
Background:
- Transition metal ions play crucial roles in catalysis and chemical reactions.
- Understanding the reaction mechanisms of metal ions with hydrocarbons is essential for developing new catalytic processes.
Purpose of the Study:
- To investigate the reaction dynamics of cobalt ions (Co+) with propane (C3H8) and its deuterated analog (C3D8).
- To elucidate the reaction pathways and product distributions using experimental and computational methods.
- To compare the reactivity of Co+ with other first-row transition metal ions like Fe+ and Ni+.
Main Methods:
- Experimental study using pulsed beams of Co+ and C3H8/C3D8 under single collision conditions.
- Time-resolved mass spectrometry to analyze product ions after a variable time delay.
- Density Functional Theory (DFT) calculations, specifically B3LYP, to determine energies and structures of reaction intermediates and transition states.
- Statistical rate modeling to interpret experimental decay times and cross-section data.
Main Results:
- Observed prompt elimination of H2 (CoC3H6+ + H2) and CH4 (CoC2H4+ + CH4) products, with H2 elimination favored in a 3:1 ratio at 0.21 eV.
- Identified long-lived CoC3H8+ complexes that predominantly decompose back to reactants or eliminate H2.
- DFT calculations, with adjusted multicenter transition state (MCTS) energies, successfully reproduced experimental decay times and collision energy-dependent cross sections.
- The theoretical model correctly predicted the preference for H2 elimination by Co+ compared to CH4 elimination, contrasting with Fe+ and Ni+.
Conclusions:
- The reaction of Co+ with propane proceeds through both prompt and complex-mediated pathways.
- DFT calculations provide accurate insights into the reaction mechanism and energy landscape.
- The observed product branching ratios are explained by the relative energies of transition states leading to H2 and CH4 elimination, differentiating Co+ reactivity from Fe+ and Ni+.
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