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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:   AlH(CH3)2 → CH4 + Al(CH3)
Reaction order:   1
Temperature:   400 - 2000 K
Rate expression:   4.85x1012 [s-1] e-377480 [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) [s-1]
400 2.47E-37
500 1.78E-27
600 6.67E-21
700 3.30E-16
800 1.09E-12
900 6.00E-10
1000 9.30E-8
1100 5.77E-6
1200 1.80E-4
1300 3.30E-3
1400 4.00E-2
1500 3.48E-1
1600 2.30E0
1700 1.22E1
1800 5.39E1
1900 2.03E2
2000 6.72E2