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High-Temperature Experimental and Theoretical Study of the Unimolecular Dissociation of 1,3,5-Trioxane
journal contribution
posted on 2015-06-25, 00:00 authored by Awad B.
S. Alquaity, Binod Raj Giri, John M.
H. Lo, Aamir FarooqUnimolecular dissociation of 1,3,5-trioxane
was investigated experimentally
and theoretically over a wide range of conditions. Experiments were
performed behind reflected shock waves over the temperature range
of 775–1082 K and pressures near 900 Torr using a high-repetition
rate time of flight mass spectrometer (TOF-MS) coupled to a shock
tube (ST). Reaction products were identified directly, and it was
found that formaldehyde is the sole product of 1,3,5-trioxane dissociation.
Reaction rate coefficients were extracted by the best fit to the experimentally
measured concentration–time histories. Additionally, high-level
quantum chemical and RRKM calculations were employed to study the
falloff behavior of 1,3,5-trioxane dissociation. Molecular geometries
and frequencies of all species were obtained at the B3LYP/cc-pVTZ,
MP2/cc-pVTZ, and MP2/aug-cc-pVDZ levels of theory, whereas the single-point
energies of the stationary points were calculated using coupled cluster
with single and double excitations including the perturbative treatment
of triple excitation (CCSD(T)) level of theory. It was found that
the dissociation occurs via a concerted mechanism requiring an energy
barrier of 48.3 kcal/mol to be overcome. The new experimental data
and theoretical calculations serve as a validation and extension of
kinetic data published earlier by other groups. Calculated values
for the pressure limiting rate coefficient can be expressed as log10 k∞ (s–1) = [15.84 – (49.54 (kcal/mol)/2.3RT)] (500–1400
K).
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Keywords
Unimolecular Dissociationdissociationtrioxaneshock tube900 Torrrate coefficientflight mass spectrometerMolecular geometriesfalloff behaviorenergy barrierMPtemperature rangekcal3LYPCCSDReaction productsshock wavesTheoretical Studyquantum chemicalSTReaction rate coefficientsexcitationperturbative treatmentdataRRKM calculations
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