Phase space theory, variational transition-state theory, and classical trajectory studies of gas-phase chemical reactions



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Texas Tech University


This dissertation is a collection of works on theories of gas-phase chemical reactions. Three main topics are included: phase space theory, microcanonical variational transitionstate theory, and the classical trajectory method. Phase space theory was applied to the reaction (H2O)OH- (CO2.H2O) HCO3-. The available experimental data on this reaction was successfully reproduced by taking into account the dissociation of the HCO3- ion using a dissociation energy of 1.8 eV, which is in good agreement with the reported value. The decomposition of the bromobenzene cation was studied using a variational method developed by Chesnavich. This study showed that the existence of multiple transitionstates strongly depends upon the transitional mode potential. A microcanonical variational method was developed and applied to two systems, HO2 and HeH2+. The HO2 study revealed that a bottleneck in the angular part of the potential can produce multiple transition-states. Also, multiple transition-states are more Ukely to exist for systems with lower well-depth. The HeH2+ study supports this trend. More detailed calculations conserving angular momentum gave similar results. A life-time estimate for the system trapped between the two transition-states was performed with a pseudo-complex assumption. For the HeH2+ system, this lifetime is equal to -200 fs, which is within the limit of experimental detection. The origin of the dynamic threshold for collision-induced dissociation was studied using the boundary trajectory method. This study showed no correlation between the curvature of the minimum energy path potential and the dynamic threshold. The results suggest that the dynamic and energetic thresholds are equal only when an exchange reaction channel is present