Theoretical Studies On Excited Potential Energy Surfaces And Nonadiabatic Dynamics For Triatomic Systems Such As CN₂,H₂O And IO₂

Molecular reaction dynamics can explore the microscopic processes of chemical reactions at the atomic and molecular level.By advanced experimental techniques or theoretical calculation methods,people can study some important elementary reactions,such as quenching reaction,electron energy transfer reaction and photodissociation reaction,which play a key role in atmospheric chemistry,combustion chemistry and interstellar chemistry and reveal detailed microscopic mechanisms.Because these chemical reactions usually involve many electronic states,the constructions of potential energy surfaces（PESs）and the study of nonadiabatic dynamics are still challenging.In this paper,we have studied the quenching reaction（CN2 system）caused by spin-orbit coupling,photodissociation reaction（H2O system）caused by conical intersection,and electron energy transfer reaction（IO2 system）including both two nonadiabatic effects.We developed the nonadiabatic representation method and build the diabatic potential energy matrix.The nonadiabatic dynamics calculations reveal the detailed micro dynamic mechanism of the reaction system.The main achievements of this paper are as follows.1.The high-precision PESs and nonadiabatic dynamics are studied in the quenching reation of CN2.The quenching reaction of CN2 is a typical spin forbidden reaction.Because this reaction exists in the earth atmosphere and extraterrestrial stars,it has been widely concerned by the scientists of atmosphere and interstellar.In this paper,the high-precision ab initio multi-reference configuration interaction（MRCI）method is used to calculate the potential energies and spin orbit couplings of CN2.The full dimensional PESs and spin-orbit couplings surfaces of the singlet and triplet states of CN2 are constructed by permutation invariant polynomials and neural network（PIPNN）method.Based on the PESs and couplings,the nonadiabatic representation is developed and the quantum dynamics are studied by an effective two-state simplified model.In this paper,the rate constants are in good agreement with the experimental values.The negative dependence on temperature at range of 20-300 K is similar to the barrierless capture process.In the study of the quenching reaction,spin-orbit couplings have only a few dozen wave numbers,however,they play important roles in this reaction system.The long-life resonance which is caused by the deep potential well on the potential energy surface,effectively increases the reaction probability.This conclusion provides valuable information for the mechanism of the intersystem crossing quenching process.2.The PESs of high-energy excited states for H₂O are constructed to explain the observations from experiment.As the prototype reaction of photodissociation process,the photodissociation process of H₂O has been widely studied by experimental and theoretical chemistry researchers in the past decades.At present,scientists are more concerned about the impact of its high-energy excited photodissociation on the origin of life.However,due to the involving of higher Rydberg electronic states in high energy excitation,it is a great challenge for theoretical calculations.In this paper,the Gaussian process method is used to fit the PESs for the lowest ten adiabatic singlet electronic states which are calculated by the multi-reference method.The structures of the global minima,conical intersections and transition states on the PESs of the high excited Rydberg states for H₂O are analized in detail.In cooperation with the researchers Xueming Yang and Kaijun Yuan from Dalian Institute of Chemical Physics,we explain several scientific problems which are related to the photodissociation of water.By studying the three body dissociation channel on the PES of state and the experimental observation of three body dissociation,it is concluded that the oxygen generation in the prebiotic atmosphere on earth mainly comes from the three body photodissociation process of water.This conclusion is of great significance to the atmospheric evolution of the planets which are in rich of water like earth.3.The high-precision nonadiabatic PESs which contain derivative and spin-orbit couplings are constructed to reveal the significant element for the electron energy transfer reaction dynamics of IO2.The electron energy transfer reaction of IO2 is an important elementary reaction in chemical oxygen iodine laser.Calculation of its rate constant plays an important role in the development of chemical oxygen iodine laser.This energy transfer process includes both conical intersections and spin-orbit effects.Twenty years ago,the former theoretical rate constant was opposite to experimental one.Until to now,the problem has not been solved.In this paper,high-level MRCI method is used to calculate the potential energies,derivative couplings and spin-orbit couplings of IO2.By using PIP-NN method,the full-dimensional PESs,derivative couplings and spin-orbit couplings surfaces of the doublet and quadruple states are constructed.Based on the PESs and the couplings,the nonadiabatic representation method is developed and the diabatic potential energy matrix is constructed.The rate constants of the electron energy transfer process at range of 10-300 K are obtained by the time-dependent wave packet quantum dynamics method.The experimental results are reproduced and the outstanding problems in the past 20 years are solved.In the study of the electron energy transfer reaction,it is also found that the slight positive temperature dependence is attributed to the effective barrier which is caused by the centrifugal barrier in the nonadiabatic process.This system with strong spin-orbit coupling effect is mainly caused by derivative coupling because the spin-orbit coupling has little relationship with the dynamics.The new results should extend understanding of energy transfer for people,provide a quantitative basis for numerical simulations of the chemical oxygeniodine laser,and have important implications in other electronic energy transfer processes.