Title:

Reduced dimensionality quantum dynamics of chemical reactions

In this thesis a reduced dimensionality quantum scattering model is applied to the study of polyatomic reactions of type X + CH4 <> XH + CH3. Two dimensional quantum scattering of the symmetric hydrogen exchange reaction CH3+CH4 <> CH4+CH3 is performed on an 18parameter doubleMorse analytical function derived from ab initio calculations at the CCSD(T)/ccpVTZ//MP2/ccpVTZ level of theory. Spectator mode motion is approximately treated via inclusion of curvilinear or rectilinear projected zeropoint energies in the potential surface. The closecoupled equations are solved using Rmatrix propagation. The statetostate probabilities and integral and differential cross sections show the reaction to be primarily vibrationally adiabatic and backwards scattered. Quantum properties such as heavylightheavy oscillating reactivity and resonance features significantly influence the reaction dynamics. Deuterium substitution at the primary site is the dominant kinetic isotope effect. Thermal rate constants are in excellent agreement with experiment. The method is also applied to the study of electronically nonadiabatic transitions in the CH3 + HCl <> CH4 + Cl(2PJ) reaction. Electrovibrational basis sets are used to construct the closecoupled equations, which are solved via Rmatrix propagation using a system of three potential energy surfaces coupled by spinorbit interaction. Ground and excited electronic surfaces are developed using a 29parameter doubleMorse function with ab initio data at the CCSD(T)/ccpV( Q+d)Zdk//MP2/ccpV(T+d)Zdk level of theory, and with basis set extrapolated data, both corrected via curvilinear projected spectator zeropoint energies. Coupling surfaces are developed by fitting MCSCF/ccpV(T+d)Zdk ab initio spin orbit constants to 8parameter functions. Scattering calculations are performed for the ground adiabatic and coupled surface models, and reaction probabilities, thermal rate constants and integral and differential cross sections are presented. Thermal rate constants on the basis set extrapolated surface are in excellent agreement with experiment. Characterisation of electronically nonadiabatic nonreactive and reactive transitions indicate the close correlation between vibrational excitation and nonadiabatic transition. A model for comparing the nonadiabatic cross section branching ratio to experiment is discussed.
