Dynamics of Pentane and Propane
Metathesis Reactions
Crossed-molecular-beam scattering is at the forefront of experimental means of investigating the fundamental reactive encounters in metathesis reactions, in which a single atom is transferred from a stable molecule to an atom or radical. Berkeley Lab researchers are exploiting a unique combination of intense, tunable VUV synchrotron radiation with the crossed-beam technique on Beamline 9.0.2 at the ALS to yield important new insights into the dynamics of hydrogen transfer (abstraction) when chlorine reacts with the saturated hydrocarbons pentane and propane.
The flux-contour map obtained for the crossed-beam reaction of chlorine and pentane, Cl + n-C5H12 --> HCl + C5H11, shows the recoil speed (radial distance) and direction (angle) of the pentyl-radical products. The blue and red circles represent the maximum speeds of the 2-pentyl radicals and 1-pentyl radicals, respectively. (Left) Abstraction of secondary hydrogen atoms yields fast, cold, forward-scattered 2-pentyl radicals via grazing collisions. (Right) Abstraction of primary hydrogen atoms yields slow, hot, backscattered 1-pentyl radicals via head-on collisions.
Free-radical abstractions of hydrogen atoms in saturated hydrocarbons are reactions of great importance in combustion, and the differing propensities for reaction of primary, secondary, and tertiary hydrogen atoms, as well as the different dynamics underlying these pathways, are central to a detailed understanding of combustion chemistry. The insights from the dramatic differences observed in the dynamics of pentane as compared to propane reactions will help build the foundation for developing accurate computer models of practical combustion systems.
Research conducted by D.A. Blank, N. Hemmi, and A. G. Suits (Berkeley Lab) and Y. T. Lee (Academia Sinica, Taiwan), using Beamline 9.0.2.
Funding: U. S. Department of Energy, Office of Basic Energy Sciences.
Publications about this experiment: D. A. Blank, N. Hemmi, A. G. Suits, and Y. T. Lee, Chem. Phys. 231, 261 (1998); N. Hemmi and A. G. Suits, J. Chem. Phys. 109(13), 5338 (1998).
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