Low energy crossed beam study of the proton transfer reactions of H/sub 3/O/sup +/ with CH/sub 3/OH and C/sub 2/H/sub 5/OH
We present a study of the title reactions over the range from 0.76 to 2.75 eV for proton transfer to methanol and at 0.99 and 1.84 eV for the ethanol system. The dynamics of proton transfer are direct at all collision energies, with the ionic products scattered in the backward direction relative to the incoming ion. The average fraction of the available energy appearing in product translation increases from 0.25 for CH/sub 3/OH/sub 2//sup +/ production at 0.76 eV to 0.44 at 2.75 eV. At 0.99 eV, the corresponding fraction for protonation of ethanol is 0.26 and increases to 0.49 at 1.84 eV. The translational energy distributions show depletion of intensity at low values of E/sub T/', suggestive of unimolecular decay of the protonated alcohols via C--O bond cleavage and elimination of H/sub 2/ across the C--O bond. Isotope effect measurements for protonation of CH/sub 3/OD and subsequent elimination of H/sub 2/ vs HD indicate the importance of a large hydride transfer contribution to the isotope effect. These results, along with statistical calculations, are employed to estimate the exit channel barrier with elimination process. Anomalously large elimination isotope effects (k/sub H//sub 2//k/sub H//sub D/ = 7) arise because of the near confluence of the CO bond cleavage and HD elimination thresholds. We find that the H/sub 2/ elimination barrier lies between 2.8 and 2.9 eV, within experimental error equal to the endothermicity of the C--O bond cleavage reaction. This result is in agreement with recent calculations of Nobes and Radom and explains the nonoccurrence of the condensation reaction between CH/sub 3//sup +/ and H/sub 2/O.
- Research Organization:
- Department of Chemistry, University of Rochester, Rochester, New York 14627
- OSTI ID:
- 6093424
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 82:5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ETHANOL
ION-MOLECULE COLLISIONS
METHANOL
OXONIUM IONS
CHARGE EXCHANGE
CHEMICAL REACTION KINETICS
MOLECULAR BEAMS
ALCOHOLS
BEAMS
CHARGED PARTICLES
COLLISIONS
HYDROXY COMPOUNDS
ION COLLISIONS
IONS
KINETICS
MOLECULAR IONS
MOLECULE COLLISIONS
ORGANIC COMPOUNDS
REACTION KINETICS
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena