Theoretical Studies For State-to-state Reaction Dynamics Of BrH₂,HNO And HOCO Systems

Initial state and final state(state-to-state)resolved dynamical studies on reactive molecular systems can reveal detailed microscopic mechanism of reactions,understand the nature of reactions deeply,and further supply the theoretical basis for how to control and utilize reactions.To investigate on molecular reaction dynamics,it is essential to solve the Schrodinger equation of nuclear motions.The highly accurate potential energy surface plays a key role in revealing the dynamics of reactions correctly.In addition,one efficient and accurate quantum mechanical method is very important as well.In this thesis,based on the highly accurate potential energy surfaces of triatomic BrH2 and HNO/HON sytems and tetratomic HOCO system,state-to-state dynamics for the H + HBr abstraction and exchange reactions,the quenching process of Br(2P1/2)+ H2,N + OH → H +NO and O + NH→ H + NO/N + OH reactions was investigated,and the detailed dynamics mechanisms were obatined.The H + HBr reaction is an important direct reaction,which has received considerable attention,both experimentally and theoretically.Based on the early adiabatic potential energy surface,the rate constants for the H + HBr reaction calculated by quantum wave packet method were 2 times larger than experimental data.Based on our newly accurate ab initio global potential energy surface,the calculated rate constants were found to be in excellent agreement with the available experimental data and much better than those obtained from a previous potential energy surface.We further investigated the H + HBr abstraction and exchange reaction at the state-to-state level.It was found that the abstraction channel is dominant at low collision energy,while the exchange channel becomes to be a major reaction channel at the relative high collision energy.It is greatly hoped that the theoretical results reported here will stimulate further theoretical and experimental explorations on this system.The excited Br(2p1/2)and H2 can lead to quenching or non-adiabatic reaction processes,which were studied using time-dependent wave packet method based on our highly accurate diabatic potential energy surfaces.It was shown that Br(2 P1/2)and H2(v)can efficiently quench to Br(2P1/2)and H2(v+1),while the probability of the non-adiabatic reaction is very small and can be neglected,which is consistent with the previous theoretical and experimental results.We also found the quenching probabilities have some oscillatory structures due to the interference of reflected flux in the isoenergetic Br(2P1/2)+ H2(v)and Br(2P3/2)+ H2(v+1)channels by repulsive potential.Meanwhile,we calculated the rate constant of Br(2P1/2)+ H2(v=0)quenching process at 300 K,and it was in good agreement with experimental values.Reactions of atoms and radicals involving the HNO and HON species play important roles in combustion,atmospheres and interstellar media.Based on our highly accurate potential energy surface a3A",firstly we calculated the rate constants of the N + OH → H + NO reaction at low temperatures,which were in excellent agreement with the newest experimental results using CRESU(Cinetique de Reaction en Ecoulement Supersonique Uniforme)technique.Then we obtained the ro-vibrational state distributions and differential cross sections of NO product by the accurate and efficient Chebyshev real wave packet method.The results were in good agreement with the theoretical results of previous potential energy surface and available experimental results,which verified high accuracy of our potential energy surface.Meanwhile,the calculated differential cross section was dominated by scattering in both the forward and backward directions,consistent with the formation of reaction intermediates.State-to-state dyneamics of the O + NH reaction was investigated on three adiabatic electronic states,namely,the X’A’,A’A" and a3 A" states.The calculated total rate constants were found to be in satisfactory agreement with the experimental values,the vibrational state distribution of NO product was different from that of experimental result,which was probably caused by significant uncertainties in the experiment reported elsewhere.In addition,inverted vibrational state distributions and significant non-reactive scattering suggested substantial non-statistical behaviors.The reaction proceeded with a complex-forming mechanism as evidenced by the near forward-backward symmetry in the differential cross section.The HOCO system has served as a tetratomic prototype for complex-forming reactions.A detailed quasi-classical trajectory study of the H + CO2→OH + CO reaction was investigated on an accurate potential energy surface X2-A’.We calculated the rate constants of this reaction at the first time,and the rate constants were found to be in good agreement with the available experimental data.The effect on the vibrational mode excitation of CO2 influencing the reaction was studied,it was shown that the excitation of the CO2 bending vibration enhanced the reaction,while the excitation in its asymmetric stretching vibration inhibited the reaction.At the state-to-state level,the ro-vibrational state distributions of the OH product were in good agreement with experimental results,while those for the CO product were much different from measurements,which probably caused by the rotational relaxation of CO in the experiment.At last,we calculated the differential cross sections and found they were dominated by forward scattering,suggesting that the lifetime of the HOCO intermediate might not be sufficiently long to render the reaction completely statistical.