Potential Energy Surface And Reaction Dynamics Studies For Systems Containing A Metal Atom

Reaction between alkali metals(alkaline earth metals)and halogen molecule is known to be dominated by Harpoon Mechanism:an electron in the alkali metal atom jumps to the hydrogen halide molecule during the course of reactive collision leading to the formation of unstable hydrogen halide anion which then undergoes quick dissociation to produce alkali halide molecule.This jump takes place near the region of curve crossing between ionic state and covalent state.As a result,the potential energy surface(PES)of ground adiabatic state is often characterized with a saddle point which serves as the bottleneck of the reactions.In this thesis,we carried out accurate quantum wave packet and quasi-classical trajectory(QCT)calculations for H + CaCl(?)Ca + HCl reaction.The vibrational energy levels of HCaCl complex also have been calculated using Lanczos algorithm.Furthermore,we construct a highly accurate ab initio potential energy surface for Li+HCl reaction,and perform a full dimension quantum dynamics calculation based on this PES.Thus,our work contains the following aspects:1 The reaction dynamics of Ca + H/DCl and Bound vibrational energy levels of HCaCl complex:We carried out accurate quantum wave packet as well as quasi-classical trajectory(QCT)calculations for Ca + H/DCl reaction using recent ab initio potential energy surface(denoted as VSGRA PES,J.Chem.Phys.122(2005)204307).The quantum mechanical calculation poses real challenge due to the presence of a deep well and the involvement of heavy atoms of the molecular system.The calculated quantum reaction probabilities show strong oscillatory energy dependence indicating involvement of many long-lived resonance states supported by the deep well.On average,the reaction probabilities monotonically increase with collision energies.In the cases Ca + HCl of J>0,Coriolis-coupling effect is found to be significant.QCT reaction probabilities have also been calculated to compare with quantum results.The overall trend is in good agreement between the two but the QCT fails to reproduce oscillatory resonance structure.By comparing the probability between Ca+HCl and its isotope reaction,the zero point energy is found to play an important role in the low collision energies.The isotopic substitution not only reduce the resonance structure of reaction probability,but also reduce the amplitude of reaction probability.In addition,the product vibrational state distributions and differential cross section are also obtained by QCT calculation.In summary,the reaction mechanism of Ca+HCl is dominated by direct mechanism.The intermediate HCaCl complex is found to support a total of 7716 vibrational energy levels up to the Ca + HCl(v'=0,j'=0)dissociation limit.The Quantum number assignments are made for several hundreds of the vibrational states.The regularity shown in the eigenfunctions of the low-lying states and the moderately high-lying states indicate a weak inter-mode coupling in the complex at least for the vibrational energy levels up to a moderately high energies(?12000 cm-1 above(0,0,0)state).At moderately high energies,we found a sign of the involvement of Fermi resonances that distorts slightly the eingenfunctions of closely spaced states.2 The quantum and quasiclassical dynamics of H + CaCl(X2?+)? HCl + Ca(1S)and D + CaCl(X2?+)? DCl + Ca(1S):We carried out accurate quantum wave packet as well as QCT calculations for H + CaCl(vi=0,ji=0)reaction to obtain the quantum and QCT reaction probabilities for several partial waves(J=0,10,and 20)as well as state resolved QCT integral and differential cross sections.The QCT reaction probabilities show excellent agreement with the quantum ones except the failure in reproducing highly oscillatory resonance structure.Despite the fact that the reaction is exothermic and the existence of a barrier that is energetically lower than the bottom of the reactant valley,the reaction probability for J=0 shows threshold-like behavior and the reactivity all through the energies is very low(<0.1 eV).The dynamical features at two different energy regions(<0.35 eV and>0.35 eV)are found to be different drastically from each other.The analyses of these results suggest that the reaction is governed by one of the two different types reaction mechanism,one is the direct mechanism at the high energy region and the other is the indirect mechanism at the low energy region by which the reaction proceeds through the long-lived intermediate complex followed by a statistical dissociation into asymptotic channels.Furthermore,the influence of initial attacking angle to the reaction dynamics and the QCT results for the product vibration state distributions and differential cross section are also discussed in detail.The effects of isotopic substitution on H + CaCl reaction have been also investigated employing the same potential energy surface(VSGRA PES).J=0 reaction probability for the D + CaCl reaction has been obtained using both the quasiclassical trajectory(QCT)and the quantum wave packet methods.The state-resolved integral as well as differential cross sections for the D + CaCl reaction have also been obtained by means of QCT method.We found isotopic substitution does not change qualitative dynamical features,leading to the similar conclusions that have been made for the H +CaCl(vi=0,ji=0)reaction,i.e.the dominance of the indirect and direct mechanisms for low(<?0.4 eV)and high(>?0.4 eV)energies respectively.Quantitatively,the isotopic substitution enhances reactivity significantly.3 A new ab initio potential energy surface of LiHCl(1A')system and quantum dynamics calculation for Li + HCL(v=0,j=0-2)?LiCl + H reaction:A new ab initio potential energy surface(PES)for the ground state of Li + HCl reactive system has been constructed by three dimensional cubic spline interpolation of 36654 ab initio points computed at the MRCI+Q/aug-cc-pV5Z level of theory.The title reaction is found to be exothermic by 5.63 kcal/mol(9 kcal/mol with zero point energy corrections),which is very close to experimental data.The barrier height,which is 2.99 kcal/mol(0.93 kcal/mol for the vibrationally adiabatic barrier height),and the depth of van der Waals minimum located near the entrance channel are also in excellent agreement with experimental predictions.This study also identified two more van der Waals minima.The integral cross sections and rate constants and their dependence on initial rotational states are calculated using exact quantum wave packet method on the new PES.They are also in excellent agreement with experimental measurements.