Dynamics of X+CH4 (X=H,O,Cl) reactions: How reliable is transition state theory for fine-tuning potential energy surfaces?

2006 ◽  
Vol 125 (6) ◽  
pp. 064312 ◽  
Author(s):  
A. J. C. Varandas ◽  
P. J. S. B. Caridade ◽  
J. Z. H. Zhang ◽  
Q. Cui ◽  
K. L. Han
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surfaces ◽  
Transition State Theory ◽  
State Theory ◽  
Fine Tuning ◽  
Energy Surfaces

scholarly journals Formation of Van Der Waals Complexes in Concerted Unimolecular Elimination Processes

2012 ◽  
Vol 2012 ◽  
pp. 1-7
Author(s):  
Faina Dubnikova ◽  
Assa Lifshitz
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surfaces ◽  
Energy Levels ◽  
Van Der Waals ◽  
State Theory ◽  
Van Der Waals Interactions ◽  
Decomposition Products ◽  
Quantum Chemical Methods ◽  
Energy Surfaces

Potential energy surfaces for three unimolecular elimination reactions: , , and were calculated using a variety of quantum chemical methods. It was shown that, in all the three cases, the transition state in the first step of the reaction leads to the production of the complex intermediates based on van der Waals interactions. In addition to the fact that the three complexes appear as intermediates on the potential energy surfaces, which means that they are not free entities, the entropy values of the two elimination products are far above those of the complexes due to their additional Sackur-Tetrode entropy. Moreover, the three vibrational frequencies of the H2O group in the (CH3)3COH complex and the H–Cl and H–F stretch frequencies in CH3CF3 and CH3CH2CH2Cl are quite different (see the various tables). The energy levels of the complexes were found to be below those of the corresponding decomposition products. Rate constants for the elimination processes were calculated from the potential energy surfaces using transition-state theory and were compared to available experimental data.

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