The Investigation For Global Potential Energy Surfaces And Quantum Dynamics Of The Triatomic Systems AlH₂、HO₂ And PH₂⁺

Molecular reaction dynamics is an important discipline for researching the processes and micromechanisms of radical reactions at the atomic-molecular level,which is relevant to important areas such as chemical vapour deposition nanomaterials,atmospheric combustion chemistry,interstellar chemistry and plasma chemistry.To investigate the reaction mechanism of molecular systems based on reaction dynamics from the theory,the premise is that the global high-precision potential energy surface of the reactant molecules in space is given.Among a variety of accurate methods for fitting potential energy surfaces,the many-body expansion（MBE）method can reproduce the same atomic substitution symmetry behaviour in polyatomic molecules very well and can fit analytic potential energy functions that remain strictly convergent in both short-and long-range interaction regions.Based on this method,we construct a global high-precision potential energy surface for typical neutral molecules AlH₂ and HO₂ in this paper through systematic electronic structure calculations,and the global potential energy surface of the excited states of the ion-molecule PH₂⁺system is then constructed,focusing on the electronic state coupling crossover and energy point of convergence in the long-range interaction region.The microscopic reaction mechanism of the dynamics of typical triatomic molecular systems is further investigated using quantum time-dependent wave packet dynamics method and quasi-classical trajectory dynamics method.The main contents of this paper are as follows:（1）The neutral molecule AlH₂ has been extensively studied as an intermediate in the chemical vapour deposition of nanomaterials and hydrogen storage materials.In this work,extensive energy points are calculated at the aug-cc-p V（Q+d）Z and aug-cc-p V（5+d）Z basis sets,based on multi-reference configuration interaction theory state-average method.The AlH₂（2²A′）global excited state potential energy surface has been constructed by fitting the analytical functions of the two-body and three-body terms according to the MBE method,and the spectral information obtained is in good agreement with the available experimental and theoretical values,indicating that the fitted new potential energy surface is accurate.Based on the new potential energy surface,the quantum time-dependent wave packet method is used to calculate the Coriolis Coupling and the Centrifugal Sudden approximation respectively,and the significant differences between them are found in the integral scattering cross sections,indicating that the Coriolis Coupling effect is more significant for the Al+H₂ reaction.In addition,the effect of different vibrational-rotational quantum numbers of the reactants on the rate constants is investigated.The vibrational-rotational excitation of the reactantH₂ molecule increases the intermolecular dipole moment and enhances the dipole-dipole mutual attraction between the reactantH₂ and Al,promoting the occurrence of reaction.（2）The neutral molecule HO₂ is of interest as an intermediate in the process of atmospheric combustion.For the HO₂ reaction system,ab initio energy points at the aug-cc-p V（Q+d）Z and aug-cc-p V（5+d）Z basis sets are obtained based on full valence complete active space self-consistent field theory and combined multi-reference configuration interaction,and extrapolated to the complete basis set limit to enhance the accuracy of the energy points.The new HO₂（X²A′′）global high-precision potential energy surface is then constructed using the MBE method,and the characteristics of the HO₂（X²A′′）global potential energy surface are discussed in detail,predicting the minimum energy reaction path,while demonstrating that O（³P）+OH（²Π）and O₂（³Σ_g^-）+H（²S）has a reasonable dissociation limit behaviour.Subsequently,the reaction mechanism of O（³P）+OH（²Π）→O₂（³Σ_g^-）+H（²S）is investigated using a quantum time-dependent wave packet method and dynamics parameters such as the integral scattering cross section and the reaction probability are obtained.These dynamics theoretical parameters can pave the way for an in-depth exploration of thermochemical collision reactions,providing a theoretical basis and reference in the study of larger O/H reaction systems.（3）PH₂⁺ion-molecules are intermediates in thermochemical collision reactions of phosphorus-containing hydrogen compounds in the interstellar atmosphere,and the P⁺+H₂→PH⁺+H reaction is important for the ionization processes of the PH_n⁺（n=0-4）series ion-molecules in interstellar clouds.In this study,using the PH₂⁺（1¹A′）ground state potential energy surface,at the MRCI level,the ab initio energy points of the triple-excited 1³A′′state and the single-excited 2¹A′are calculated using the full valence fully active space（FVCAS）as the reference wave function and in combination with the state averaging method.The global high-precision potential energy surfaces for the 1³A′′and 2¹A′states are constructed using MBE method,and the spectral datas obtained for the two-body and three-body terms are consistent with the available experimental and theoretical datas.It is shown that there is a ¹Σ_g⁺state simplification for the potential energy surfaces of the 1¹A′and 1³A′′states in linear configurations,and a ²Πstate simplification in the dissociation limit for the potential energy surfaces of the 1³A′′and2¹A′states in linear configurations.The positions of the crossings of the adiabatic potential energy surfaces of the 1¹A′and 2¹A′states are given according to the dissociation scheme of the three lowest electronic states.For the chemical collision reactions in the P⁺+H₂ system,the 1¹A′state is the easiest to occur,followed by the1³A′′state,and the most difficult to react is the 2¹A′state which has a high reaction potential.