Study Of The Rates For Reactions In Gas Phase And On Metal Surface With Quantum Instanton Theory

The quantum instanton method is a short time approximation of the flux-flux correlation function,and it treats the Boltzmann operator quantum mechanically which includes delocalization,zero-point energy and tunneling effects.Together with path integral Monte Carlo and adaptive umbrella sampling,the quantum instanton method can be applied to complex chemical reactions with large numbers of degrees of freedom,and is expected to give accurate rate constants and kinetic isotope effects.In the present paper,the rates for reactions in gas phase and on metal surface have been investigated with the quantum instanton method.The specific research contents are as follow:?1?The dissociation rates of phenol through the excited S₁ state are calculated with the quantum instanton method in full dimensionality.The Arrhenius plot of the rates shows that the quantum tunneling dominates the O-H bond dissociation at low temperatures.The degrees of freedom of phenyl ring?C₆H₅?play extremely important roles in the dissociation of phenol.Fixing the phenyl ring at the equilibrium geometry can only provide reliable rates between 400 and 800 K.The motions of phenyl ring have an impact on enhancing the dissociation by lowering the free energy barrier.The larger the amplitudes of the phenyl ring motions are,the more the free energy barrier will be reduced.The dissociation rates of C₆H₅OH are much larger than those of C₆H₅OD,which is due to the zero-point energy and entropy effects.?2?The direct and steady state dissociation rates of H₂ on H precovered Ni?100?surface are calculated by quantum instanton method.Both the direct and steady state dissociation rates on H precovered Ni?100?are smaller than those on the clean Ni?100?.This is because the repulsive interaction between H₂ and the preadsorbed H raises the potential energy barrier.Moreover,this repulsive interaction is inversely proportional to the distance between H₂ and the preadsorbed H.Owing to the classical relaxation and entropy effect of Ni atoms,the lattice motion promotes H₂ dissociation by lowering the free energy barrier,but it hinders H₂ recombination by raising the free energy barrier.There are remarkable kinetic isotope effects for the dissociation process,which is due to the entropy and quantum tunneling effects.However,no kinetic isotope effect is obtained for the recombination process.Through the above researches,we have explored the quantum dynamics effects in photodissociation of phenol,and revealed the surface coverage,lattice motion,arrangement and kinetic isotope effects in H₂ dissociation on Ni?100?.