Quantum Chemical Studies and Kinetics of Gas Reactions

Abstract

Potential energy surfaces and reaction mechanisms were calculated using various computational methods such as density-functional and wave-function methods. High-level computational methods were used to obtain accurate rate constants. Theoretical background and computational methods are introduced in Chapter 1. Chapter 2 and Chapter 3 show potential energy surface and kinetic calculations of important atmospheric reactions. Chapter 4 covers the theoretically challenging molecule F2NOF which has not yet been synthesized experimentally. The potential energy surface and the rate constants for reaction of XO (X=Cl, Br, I) with dimethyl sulfide (DMS) have been computed at high levels of theory in Chapter 2. Natural bond orbital (NBO) analysis of XO-DMS and the branching ratios of the each pathways are computed. In Chapter 3 the reaction of NO with ClO has been studied theoretically using density-functional and wave-function methods (B3LYP and CCSD(T)). Variational transition-state theory was used to calculate the rate constant for disappearance of reactants (kdis) and for formation of products (kobs) in the range of 200-1000K at the high- pressure limit. The mechanism of dissociation of F2NOF has been studied using various computational methods in Chapter 4. Rate constant calculations have been performed to understand the product formation. The calculated results showed that the formation of F3NO is favored thermodynamically but not favored kinetically.