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Title: Dynamics study of the reaction OH{sup -}+C{sub 2}H{sub 2}{yields}C{sub 2}H{sup -}+H{sub 2}O with crossed beams and density-functional theory calculations

Abstract

The proton transfer reaction between OH{sup -} and C{sub 2}H{sub 2}, the sole reactive process observed over the collision energy range from 0.37 to 1.40 eV, has been studied using the crossed beam technique and density-functional theory (DFT) calculations. The center of mass flux distributions of the product C{sub 2}H{sup -} ions at three different energies are highly asymmetric, characteristic of a direct process occurring on a time scale much less than a rotational period of any transient intermediate. The maxima in the flux distributions correspond to product velocities and directions close to those of the precursor acetylene reactants. The reaction quantitatively transforms the entire exothermicity into internal excitation of the products, consistent with an energy release motif in which the proton is transferred early, in a configuration in which the forming bond is extended. This picture is supported by DFT calculations showing that the first electrostatically bound intermediate on the reaction pathway is the productlike C{sub 2}H{sup -}{center_dot}H{sub 2}O species. Most of the incremental translational energy in the two higher collision energy experiments appears in product translational energy, and provides an example of induced repulsive energy release characteristic of the heavy+light-heavy mass combination.

Authors:
; ;  [1]
  1. Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States)
Publication Date:
OSTI Identifier:
20783251
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 124; Journal Issue: 12; Other Information: DOI: 10.1063/1.2179799; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACETYLENE; CHEMICAL BONDS; COLLIDING BEAMS; DENSITY FUNCTIONAL METHOD; EV RANGE 01-10; EXCITATION; HYDROXIDES; MOLECULE COLLISIONS; REACTION KINETICS; TRANSFER REACTIONS; WATER

Citation Formats

Liu Li, Li Yue, and Farrar, James M. Dynamics study of the reaction OH{sup -}+C{sub 2}H{sub 2}{yields}C{sub 2}H{sup -}+H{sub 2}O with crossed beams and density-functional theory calculations. United States: N. p., 2006. Web. doi:10.1063/1.2179799.
Liu Li, Li Yue, & Farrar, James M. Dynamics study of the reaction OH{sup -}+C{sub 2}H{sub 2}{yields}C{sub 2}H{sup -}+H{sub 2}O with crossed beams and density-functional theory calculations. United States. doi:10.1063/1.2179799.
Liu Li, Li Yue, and Farrar, James M. Tue . "Dynamics study of the reaction OH{sup -}+C{sub 2}H{sub 2}{yields}C{sub 2}H{sup -}+H{sub 2}O with crossed beams and density-functional theory calculations". United States. doi:10.1063/1.2179799.
@article{osti_20783251,
title = {Dynamics study of the reaction OH{sup -}+C{sub 2}H{sub 2}{yields}C{sub 2}H{sup -}+H{sub 2}O with crossed beams and density-functional theory calculations},
author = {Liu Li and Li Yue and Farrar, James M.},
abstractNote = {The proton transfer reaction between OH{sup -} and C{sub 2}H{sub 2}, the sole reactive process observed over the collision energy range from 0.37 to 1.40 eV, has been studied using the crossed beam technique and density-functional theory (DFT) calculations. The center of mass flux distributions of the product C{sub 2}H{sup -} ions at three different energies are highly asymmetric, characteristic of a direct process occurring on a time scale much less than a rotational period of any transient intermediate. The maxima in the flux distributions correspond to product velocities and directions close to those of the precursor acetylene reactants. The reaction quantitatively transforms the entire exothermicity into internal excitation of the products, consistent with an energy release motif in which the proton is transferred early, in a configuration in which the forming bond is extended. This picture is supported by DFT calculations showing that the first electrostatically bound intermediate on the reaction pathway is the productlike C{sub 2}H{sup -}{center_dot}H{sub 2}O species. Most of the incremental translational energy in the two higher collision energy experiments appears in product translational energy, and provides an example of induced repulsive energy release characteristic of the heavy+light-heavy mass combination.},
doi = {10.1063/1.2179799},
journal = {Journal of Chemical Physics},
number = 12,
volume = 124,
place = {United States},
year = {Tue Mar 28 00:00:00 EST 2006},
month = {Tue Mar 28 00:00:00 EST 2006}
}
  • The reactions between O{sup -} and C{sub 2}H{sub 2} have been studied using the crossed-beam technique and density-functional theory (DFT) calculations in the collision energy range from 0.35 to 1.5 eV (34-145 kJ/mol). Both proton transfer and C-O bond formation are observed. The proton transfer channel forming C{sub 2}H{sup -} is the dominant pathway. The center-of-mass flux distributions of the C{sub 2}H{sup -} product ions are highly asymmetric, with maxima close to the velocity and direction of the precursor acetylene beam, characteristic of direct reactions. The reaction quantitatively transforms the entire reaction exothermicity into internal excitation of the products, consistentmore » with mixed energy release in which the proton is transferred in a configuration in which both the breaking and the forming bonds are extended. The C-O bond formation channel producing HC{sub 2}O{sup -} displays a distinctive kinematic picture in which the product distribution switches from predominantly forward scattering with a weak backward peak to sideways scattering as the collision energy increases. At low collision energies, the reaction occurs through an intermediate that lives a significant fraction of a rotational period. The asymmetry in the distribution leads to a lifetime estimate of 600 fs, in reasonable agreement with DFT calculations showing that hydrogen-atom migration is rate limiting. At higher collision energies, the sideways-scattered products arise from repulsive energy release from a bent transition state.« less
  • The reactions between OH{sup +}({sup 3}{sigma}{sup -}) and C{sub 2}H{sub 2} have been studied using crossed ion and molecular beams and density functional theory calculations. Both charge transfer and proton transfer channels are observed. Products formed by carbon-carbon bond cleavage analogous to those formed in the isoelectronic O({sup 3}P)+C{sub 2}H{sub 2} reaction, e.g., {sup 3}CH{sub 2}+HCO{sup +}, are not observed. The center of mass flux distributions of both product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor acetylene beam, characteristic of direct reactions. The internal energy distributions of themore » charge transfer products are independent of collision energy and are peaked at the reaction exothermicity, inconsistent with either the existence of favorable Franck-Condon factors or energy resonance. In proton transfer, almost the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the proton is transferred with both the breaking and forming bonds extended. Most of the incremental translational energy in the two higher-energy experiments appears in product translational energy, providing an example of induced repulsive energy release.« less
  • The close-coupling hyperspherical (CCH) exact quantum method was used to study the title barrierless reaction up to a collision energy (E{sub T}) of 0.75 eV, and the results compared with quasiclassical trajectory (QCT) calculations to determine the importance of quantum effects. The CCH integral cross section decreased with E{sub T} and, although the QCT results were in general quite similar to the CCH ones, they presented a significant deviation from the CCH data within the 0.2-0.6 eV collision energy range, where the QCT method did not correctly describe the reaction probability. A very good accord between both methods was obtainedmore » for the OH{sup +} vibrational distribution, where no inversion of population was found. For the OH{sup +} rotational distributions, the agreement between the CCH and QCT results was not as good as in the vibrational case, but it was satisfactory in many conditions. The kk{sup '} angular distribution showed a preferential forward character, and the CCH method produced higher forward peaks than the QCT one. All the results were interpreted considering the potential energy surface and plots of a representative sampling of reactive trajectories.« less
  • Theoretical estimates of reactive cross sections for O({sup 1}D) + H{sub 2}(X,{nu} = 0j){yields}OH(X) + H({sup 2}S), with H{sub 2} rotational quantum numbers j = 0 and 1, are obtained for a range of collision energies, E{sub col}. Crossed molecular beam measurements are also used to infer the ratio, r{sub 1,0}, of the j = 1 and 0 cross sections at E{sub col} = 0.056 eV. The theory indicates that the 1 {sup 1}A{prime} potential surface is the most important one. However, the 2 {sup 1}A{prime} and 1 {sup 1}A{prime} surfaces can also contribute. Adiabatic dynamics on the 1 {supmore » 1}A{prime} surface, particularly at E{sub col} above its 0.1 eV barrier to reaction plays a role. The 2 {sup 1}A{prime} surface, while not correlating with ground electronic state products, can still lead to products via nonadiabatic interactions with the 1 {sup 1}A{prime} surface. Many quantum dynamics and quasiclassical classical trajectory calculations are carried out. Accurate, ab initio based potential energy surfaces are employed. Quantum cross sections are based on helicity decoupled wave packet calculations for several values of total angular momentum. Nonadiabatic wave packet and trajectory surface hopping calculations, where appropriate, are carried out. An interesting, subtle picture emerges regarding the energy dependence of r{sub 1,0}. The theoretical results indicate, somewhat surprisingly, that, for E{sub col}<0.1 eV,r{sub 1,0} can be less than unity owing to the anisotropy of the ground state potential. Electronically excited states and nonadiabatic effects contribute to the overall cross sections for E{sub col}>0.1 eV, but the full r{sub 1,0} is only weakly sensitive to excited states. Our experimentally inferred r{sub 1,0} at E{sub col} = 0.056 eV, 0.95{+-}0.02, is in quantitative agreement with our best calculation, which suggests that the effect of potential anisotropy is correctly described by theory. The relation between these results and previous experimental findings is discussed.« less
  • The reaction of Re{sub 2}O{sub 7} with XeF{sub 6} in anhydrous HF provides a convenient route to high-purity ReO{sub 2}F{sub 3}. The fluoride acceptor and Lewis base properties of ReO{sub 2}F{sub 3} have been investigated leading to the formation of [M][ReO{sub 2}F{sub 4}] [M = Li, Na, Cs, N(CH{sub 3}){sub 4}], [K][Re{sub 2}O{sub 4}F{sub 7}], [K][Re{sub 2}O{sub 4}F{sub 7}]{center_dot}2ReO{sub 2}F{sub 3}, [Cs][Re{sub 3}O{sub 6}F{sub 10}], and ReO{sub 2}F{sub 3}(CH{sub 3}CN). The ReO{sub 2}F{sub 4}{sup {minus}}, Re{sub 2}O{sub 4}F{sub 7}{sup {minus}}, and Re{sub 3}O{sub 6}F{sub 10{sup {minus}} anions and the ReO{sub 2}F{sub 3}(CH{sub 3}CN) adduct have been characterized in the solidmore » state by Raman spectroscopy, and the structures [Li][ReO{sub 2}F{sub 4}], [K][Re{sub 2}O{sub 4}F{sub 7}], [K][Re{sub 2}O{sub 4}F{sub 7}]{center_dot}2ReO{sub 2}F{approximately}3}, [Cs][Re{sub 3}O{sub 6}F{sub 10}], and ReO{sub 3}F(CH{sub 3}CN){sub 2}{center_dot}CH{sub 3}CN have been determined by X-ray crystallography. The structure of ReO{sub 2}F{sub 4}{sup {minus}} consists of a cis-dioxo arrangement of Re-O double bonds in which the Re-F bonds trans to the oxygen atoms are significantly lengthened as a result of the trans influence of the oxygens. The Re{sub 2}O{sub 4}F{sub 7}{sup {minus}} and Re{sub 3}O{sub 6}F{sub 10}{sup {minus}} anions and polymeric ReO{sub 2}F{sub 3} are open chains containing fluorine-bridged ReO{sub 2}F{sub 4} units in which each pair of Re-O bonds are cis to each other and the fluorine bridges are trans to oxygens. The trans influence of the oxygens is manifested by elongated terminal Re-F bonds trans to Re-O bonds as in ReO{sub 2}F{sub 4}{sup {minus}} and by the occurrence of both fluorine bridges trans to Re-O bonds. Fluorine-19 NMR spectra show that ReO{sub 2}F{sub 4}{sup {minus}}, Re{sub 2}O{sub 4}F{sub 7}{sup {minus}}, and ReO{sub 2}F{sub 3}(CH{sub 3}CN) have cis-dioxo arrangements in CH{sub 3}CN solution. Density functional theory calculations at the local and nonlocal levels confirm that the cis-dioxo isomers of ReO{sub 2}F{sub 4}{sup {minus}} and ReO{sub 2}F{sub 3}(CH{sub 3}CN), where CH{sub 3}CN is bonded trans to an oxygen, are the energy-minimized structures. The adduct ReO{sub 3}F(CH{sub 3}CN){sub 2}{center_dot}CH{sub 3}CN was obtained by hydrolysis of ReO{sub 2}F{sub 3}(CH{sub 3}CN), and was shown by X-ray crystallography to have a facial arrangement of oxygen atoms on rhenium.« less