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Author(s):   Walch, S.P.; Dateo, C.E.
Title:   Thermal Decomposition Pathways and Rates for Dimethylaluminum Hydride
Journal:   J. Phys. Chem. A
Volume:   105
Page(s):   5260 - 5265
Year:   2001
Reference type:   Journal article
Squib:   2001WAL/DAT5260-5265

Reaction:   CH4 + Al(CH3) → AlH(CH3)2
Reaction order:   2
Temperature:   400 - 2000 K
Rate expression:   1.11x10-10 [cm3/molecule s] e-295976 [J/mole]/RT
Category:  Theory
Data type:   Ab initio
Pressure dependence:   Rate constant is high pressure limit
Comments:   Geometries and frequencies using CASSCF/cc-pVDZ method. Unscaled frequencies used. Energies of reactants, products, transition states calculated using CCSD(T)/cc-pVTZ extrapolated to the CBS limit using Martin-Schwartz three point extrapolation using MP2/cc-pVnZ(n=2,3,4) energies. Calculations also done with ICCI+Q method. For DMAlH dimer B3LYP/6-31G calculations were used (for some cases CCSD(T) were used also). For reactions with barriers, conventional transition state theory was used employing the program Polyrate. For barrierless reactions, a Gorin model was used. It is not explicitly stated apparently, but it is likely that CCSD(T) energies were used for TST calculations, while ICCI+Q calculations were just a double check on the validity of the CCSD(T) energies. It is unclear in paper regarding difference between bimolecular transition state geometry for DMAlH+DMAlH = Al2Me2+H2 (Ea 34 kcal/mol Hr 1 kcal/mol) as opposed to that for dimer decomposition transition state for (DMAlH)2 = Al2Me2+H2 (Ea 75 kcal/mol Hr 27 kcal/mol). Dimer decomposition appears to be given and described, while bimolecular transition state does not seem to be given nor described.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) [cm3/molecule s]
400 2.49E-49
500 1.34E-41
600 1.90E-36
700 9.12E-33
800 5.25E-30
900 7.37E-28
1000 3.85E-26
1100 9.79E-25
1200 1.45E-23
1300 1.42E-22
1400 1.01E-21
1500 5.48E-21
1600 2.41E-20
1700 8.94E-20
1800 2.86E-19
1900 8.10E-19
2000 2.07E-18