title: 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.
abstract: The rate coefficients for the forward and reverse proton-transfer reactions C(2)H(4) + H(3)O(+) ⇄ C(2)H(5)(+) + H(2)O 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 H(3)O(+) and C(2)H(4). 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.affiliation: Department of Chemistry and Biochemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, United States. markasmith@nsm.uh.edu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Smith
authors.forename: Bing
authors.initials: B
authors.lastname: Yuan
authors.forename: Andrei
authors.initials: A
authors.lastname: Sanov