The Construction Of Global Potential Energy Surface And Dynamics For Small Sulfur Containing Molecular System

Recently,due to the important role in the atmosphere environment,researchers have beeen paying widely attention to the important radical reaction dynamics,and sulfur-containing molecular systems have already become the focus of the research.However,in order to thoroughly study the properties and the reaction dynamics of sulfur-containing molecular systems,construction of global molecular potential energy surface?PES?with high accuracy is the first priority,since PES is the basis of exploring molecular structure,spectroscopy and vibrational energies,etc.,and it also is the cornerstone of molecular reaction dynamics studies.Studies on the reaction dynamics of the important sulfur-containing molecular reaction dynamics,which is an important research subject of atomic and molecular physics,is of great significance for revealing the micro reaction mechanism.The main goal of the current project includes two parts:?1?Constructing the global PESs with high accuracy for the ground and excited states of small sulfur-containing molecular systems?HCS?X²A?/A²A??,HS₂?A²A'?and S₂?a¹?_g/b¹?_g⁺??to obtain the electronic structure,energies and vibrational frequencies of the molecular equilibrium,transition states and saddle points.?2?Using the quasi-classical trajectory?QCT?method to study the relevant reaction dynamics based on the newly developed PESs,to calculate the dynamics parameters such as the rate constants,differential cross sections and integral cross sections?ICS?,and to analyze the isotope effect,which can reveal the microscopic reaction mechanism of small sulfur-containing molecular systems.We used the MRCI level of theory with aug-cc-p VXZ and aug-cc-p V?X+d?Z?X=T,Q,5,6?basis sets of Dunning to calculate the potential energy curves?PECs?of S₂?a¹?_g/b¹?_g⁺?.For further study,all the PECs are then fitted to analytical PES functions?APEFs?by double many-body expansion?DMBE?.In order to correct the basis-set superposition error,the ab initio energies calculated in this way are then extrapolated to the complete basis set?CBS?limit.In order to test the quality of the APEFs,we calculate the spectroscopic constants?D_e,R_e,?_e,B_e,?_e and?_e?_e?of S₂?a¹?_g/b¹?_g⁺?.By solving the radial Schr?dinger equation of the nuclear motion with the program Level 7.5,we obtain the vibrational energy levels,classical turning points,rotation constant and six centrifugal distortion constants of the S₂?a¹?_g/b¹?_g⁺?.The hydrogen,carbon,and sulfur are among the nine most abundant atoms in our universe.As the simplest neutral molecules containing these three atoms,the thioformyl?HCS?and isothioformyl?HSC?not only are the fundamental reaction intermediate in combustion processes,but also play an important role in molecular formation processes at interstellar clouds.Therefore,a large number of studies on HCS molecules have been conducted experimentally and theoretically.Most of the works are mainly on the ground state?X²A??PES or the equilibrium structures of the excited state?A²A??.However,the C+SH?H+CS reaction based on full-dimensional PES is very important in the atmosphere.To our knowledge,no global full dimensional PES has so far been reported for the A²A?state of HCS.For the ground state,the calculation is used with smaller basis sets and the inaccurate method.So we construct the accurate global adiabatic PESs for the ground and first excited state of HCS.The ab initio calculations are carried out at the MRCI level of theory with aug-cc-p VXZ?x=Q,5?basis sets of Dunning.In order to correct the basis-set superposition error,the ab initio energies calculated in this way are then extrapolated to the CBS limit.Based on this,the least square method is used to fit such corrected energy points.In the fitting process,many-body expansions?MBE?and Aguado-Paniagua?AP?functions are used to describe the interaction between atoms.The root mean squared deviation?RMSD?values are 0.988 and 0.846 kcal/mol,respectively.Based on the new PES,we also study the C?³P?+SH/D/T?X²???H/D/T+CS?X¹?⁺?and C?³P?+SH?X²???v=0-20,j=0??H+CS?X¹?⁺?reactions.At the same time,the C?³P?+SH?X²???H?²S?+CS?a³??reaction is also studied by QCT theory.It has long been recognized that reduced sulfur-bearing species play an important role in the Earth's atmosphere,in biochemistry and combustion chemistry.Amongst the various reduced sulfur-bearing species,thiosulfeno radical HS₂,hydrogen disulfide H₂S_2,thiozone S₃,etc.have aroused considerable interest.Most of the works are mainly on the ground state?X²A??PES or the equilibrium structures of the excited state?A²A'?.To our knowledge,no global full dimensional PES has so far been reported for the A²A'state of HS₂.So we construct the accurate global adiabatic PESs for the first excited state of HS₂.The MRCI level of theory with aug-cc-p VXZ?x=Q,5?basis sets of Dunning are used to calculate the ab initio energy points of HS₂?A²A??.In order to correct the basis-set superposition error,the ab initio energies calculated in this way are corrected by DMBE/SEC.Then we use the MBE and DMBE with least square method to obtain the APEFs.In order to exam the PES,we calculate the equilibrium structure,transition state and the saddle points of HS₂?A²A??,as well as the spectroscopic constants of HS?X²??and S₂?a¹?_g?.For the MBE:R₁=3.955 a₀,R₂=2.561 a₀ and R₃=4.889 a₀.The agreement is very good with experiment work.We also calculate the features of three saddle points?SP?:SP1(D_?h),SP2(C_?v)and SP3(C_?v),and two transition states:TS1(C_2v)and TS2(C_?v).By comparison,it is found that the stationary points obtained by the two fitting methods agree well with each other.Based on the new PES,the H+S₂?a¹?_g??v=0-2,j=0??HS+S reaction is studied by QCT theory.