Theoretical Study Of The Stereodynamic For The Reaction Ca+HCl

Recently，potential-energy-surface (PES) calculations and reaction-dynamic studies ofhave been the subject of experimental and theoretical studies. Moreover, the reaction M+HX�'MX+H (M=Be, Mg, Ca, Sr, Ba; X=F, Cl, Br, I) shows interesting dynamical features, andmany studies of this reaction family have been done theoretically and experimentally. Beinga typical reaction of “Harpoonlike” models mechanism and H+HL HH+Lreaction，thereactionCa+HCl�'CaCl+H that involves an alkali-earth atom and a hydrogen halide hasbeen considered to analyze the influence of the initial state of the reactants and its effect onthe final state distribution. The Ca–HCl complex was first detected by Visticot et al. byobserving the fluorescence of CaCl molecules in a supersonicbeam/laser-ablationexperiment, Soep et al. suggested that the equilibrium configuration of the Ca–HCl complexin itsground electronic state is linear, with the distance betweenthe Ca atom and the HClcenter of mass being about3.5. In the ground electronic state, the reaction of calcium withhydrogen chloride was found to be endoergic, with the standard enthalpy change of38kJ/mol，The ground-state dissociation energy D0of the Ca–HCl complex was determinedexperimentally by Menéndez et al to be150meV，Using an empirical potential energyfunction describing the interaction between the Ca and HCl moieties, de Castro Vítores et al.estimated the binding energy of the Ca–HCl complex to be about125meV at the linearequilibrium configuration73meV as averaged over the molecular orientation of HCl. As weall know, the research of the vector properties of has a pivotal role in the molecular reactiondynamics, it give the many information that scalar properties can not provided, onlycombining these can obtain get the fullest picture of the reaction mechanism. As far as weknow, most studies in the previous work on the Ca+HCl reaction mainly focuses on thescalar properties, such as reaction probabilities, cross sections,the overall rate constant,while there are few reports about the chemical reaction stereodynamics, such as velocity andangular momentum. Only by understanding the scalar and vector properties together, can the fullest picture of the scattering dynamics emerge.To get the fullest picture of the scatteringdynamics emerge, in this Letter we present the influence of collision energies on thestereodynamics for the reaction Ca+HCl�'CaCl+H.For molecular reaction dynamics calculations, the potential energy surface is the basisand premise for the discussion of all issues, but building accurate polyatomic systemfull-dimensional potential energy surface itself is a very challenging problem. Obtainingrealistic CaHCl PES has revealed to be rather difficult,there is no accurate ab initiocalculation of the ground electronic state of CaHCl, possibly because it is highly endoergicand it exists large changes in the ionic character along the reaction paths, Most PES’s arebased on semiempirical approaches or on models such as thediatomics-in-molecules(DIMs)method, the accurate ab initio PES for the CaHCl system ismore difficult to develop.Verbockhaven et al. reported the global potential-energy surface ofthe CaHCl system in2005，describing the full reaction from Ca(4s~2,~1S)+HCl reactants toCaCl（X~2Σ）+H products, this surface is based on accurate ab initio calculations using themultireference configuration-interaction method(MRCI+Q) and the coupled-clustermethod(CCSD(T)), theoretical ab initio study on the structure and energetics of the Ca–HClcomplex is presented.then Cristina Sanz et al. studied the reaction probability, the infraredexcitation and charge-transfer contribution of the Ca+HCl(v, j) reactive collisions usingwave-packet calculations based on the PES, the reaction seems to follow a directmechanism，Only when the energy is near the threshold some resonances appear. Koput etal. reported an accurate characterization of the structure, three-dimensional potential energysurface, and vibration-rotation energy levels of the Ca–HCl complex in its ground electronicstate using the CCSD（T）method in2010, but the PES can not used in calculating onstereodynamics for the reaction Ca+HCl.To get the fullest picture of reaction mechanics, we describe the scalar and vectorproperties for the reaction Ca+HCl on the G.Verbockhaven PES using quasi-classicaltrajectory method, the stereodynamics of the reaction of Ca+HCl has been calculated atthree different collision energies and isotopic substitution, effect of the reagent vibrationand rotation on stereodynamics for Ca+HCl reactions have been successfully studied. The extensive studies can help us to study the complex reactions. This dissertation is composedof the following seven parts:The first chapter introduces the research progress of the Ca+HCl system, In Chapter2, the development of the molecular reaction dynamics and stereodynamics and theirpresent situation are presented.In Chapter3, the basic theories of constructions of potential energy surfaces (PESs) forand potential energy function for ground molecule are given. the main concepts of thedynamics reactions are introduced, We calculate the reactive time, energy distribution andfind that the reaction is mainly governed by direct reactive mechanism and direct reactivemechanism takes more fraction, when Ecin lower energy, the reaction is mainly governedby in direct reactive mechanism,the long-lived complexes corresponding to CaHClmetastable states in the indirect reactive mechanism are formed during trajectories aretrapping by effective deep potential well at low Ec. Trajectories with high energy is difficultto trap and the direct reactive mechanism takes the dominate place at high Ec. the results arein good agreement with the previous result that Cristina Sanz predicted.In the Chapter4, the dynamical mechanisms of the Ca+HCl (v=0, j=0)�'CaCl+H onthe Verbockhaven PES are calculated, the influences of collision energy on stereodynamicqualities are discussed. The results indicate that the product is almost forwards andbackwards scattering for the collision energy of0.6eV，With the increase of collisionenergy, the product is preferentially sideways and backwards scattering. the values of<P2(cosθ)> which are close to-0.5, suggesting that j′is preferentially polarized andperpendicular to the reagent relative velocity. the rotational polarization of product CaClpresents different characters for the different collision energies, the effects of collisionenergies on the vector properties are not obvious, these discrepancies may be ascribed to theheavy-heavy-light (HHL) mass combination and the constructions of the potential energysurface.In the Chapter5, firstly, the reactant-vibration-excitation effect on the reaction Ca+HCl(v=0-3, j=0)�'CaCl+H, the calculation results show that the vibraional quantum numberhas a considerable influence on the distribution of the k-j vector correlation, when the reagent molecule HCl is in the excited vibration states，the product rotational alignmenteffect of CaCl becomes stronger and the orientation effect along the negative direction ofy-axis becomes unobvious,The CaCl product mainly tends to the backward scattering as thev increases. the reactant-rotation-excitation effect on the reaction Ca+HCl (v=0, j=0)�'CaCl+H, the calculation results show that the vibraional quantum number has aconsiderable influence on the distribution of the k-j vector correlation, when the reagentmolecule HCl is in the excited vibration states，the product rotational alignment effect ofCaCl becomes stronger and the orientation effect along the negative direction of y-axisbecomes unobvious,The CaCl product mainly tends to the backward scattering as the vincreases. Secondly,the effect of the reactant rotational excitation (j=0,1,2,3,4) on thestereodynamical properties of the reactionCa+HCl�'CaCl+H have been investigated,rotational energy show little effect on product rotational angular momentum,the degree ofscattering/the alignment/orientation product becomes not obvious.In the Chapter6, the relevant conclusions of the isotope effect on the reaction Ca+HCl/DCl/TCl�'CaCl+H/D/T have been obtained, the calculated results indicate resultsisotopic substituted effect has more influence on the product rotational angularmomentum.the alignment and orientation of the product CaCl are investigated in detail withstereodynamics, the trend of forward scattering becomes weaker and the trend of backwardscattering becomes stronger, the degree of the alignment/orientation product becomesweaker.In Chapter7, Summary and Outlook of the scalar properties and vector properties ofthe reactions of the Ca+HCl reaction have been introduced，some conclusions of theCa+HCl reaction are presented.