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Variable-Temperature Rate Coefficients of Proton-Transfer Equilibrium Reaction C2H4 + H3O+ ⇄ C2H5+ + H2O Measured with a Coaxial Molecular Beam Radio Frequency Ring Electrode Ion Trap

The rate coefficients for the forward and reverse proton-transfer reactions C2H4 + H3O+ ⇄ C2H5+ + H2O are studied with respect to independent varied neutral molecule and ion temperatures. The measurements are performed using a coaxial molecular beam radio frequency ring electrode ion trap at trap temperatures down to 23 K and beam temperatures up to 450 K. The temperature-dependent rate coefficients suggest that in this temperature window, the reaction proceeds through a statistically equilibrated complex. In order to explain the observed rate coefficients, a new type of reaction temperature was defined in these studies that considered collisional and internal (rotational and vibrational) degrees of freedom of both H3O+ and C2H4. The enthalpy and entropy of the equilibrium reaction deduced from a Van't Hoff plot are ΔH = (5.1 ± 0.5) kJ·mol–1 and ΔS = (−15.0 ± 0.9) J·mol–1·K–1, respectively.

Authors:   Mark A. Smith; Bing Yuan; Andrei Sanov
Journal:   Journal of Physical Chemistry A
Year:   2012
DOI:   10.1021/jp306372v
Publication date:   16-Nov-2012
Facts, background information, dossiers
  • temperature
  • Proton
  • entropy
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