A. Alquaity, B. Giri, J. Lo, A. Farooq
Journal of Physical Chemistry A, 119, pp. 6594-6601, (2015)
Unimolecular 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).