Theoretical Study Of The Dynamics For The Reaction O+H₂⁺

Due to the important role in high energy physics, astrophysics and plasma physics, ion-molecule reaction has attracted much attention. In recent years, O+H₂⁺ reaction has been studied in many theoretical and experimental investigations. Being a typical ion-molecule reaction, the O+H₂⁺ reaction has many attractive features and has great value for us to study. Based on the the first excited（12A’） PES of Paniagua et al. constructed, we plotted the contour map. We can see that there is a shallow well with the insertion of the O atom into the middle of the H₂⁺ bond. We employ the QCT method to study the stereodynamics of the title reaction. We have investigated the influences of collision energy, ro-vibration excitation and isotopic effect on the stereodynamics properties of the O+H₂⁺→OH⁺H⁺ reaction.Firstly, we studied the dynamics properties of the reaction with different collision energies. In general, the effects were obvious on the PES. The reaction probability had a decrease trend with the increase of collision energy. It could be ascribed to the well of the excited state PES（12A’） of the reaction O + H₂⁺→ OH + H⁺, in which there was no energy threshold. The integral cross section of the title reaction decreased gradually with the increase of collision energy arises from the barrierless character of the PES. The alignment and orientation effects were very obvious and parallelled in the direction of the scattering plane, which indicated that the product molecule had a preference to the “in-plane” mechanism. Due to the low potential well, the distributions of forward and backward scattering were asymmetric and the reaction was not a typical insertion one. The formation of intermediate complex indicated that the indirect mechanism played an important role during the reaction process.Then, in the same collision energy of 0.2e V, when the vibrational effect strengthened, the alignment and orientation effects of the O+H₂⁺→OH⁺H⁺ reaction were sensitive to the reactant vibrational excitation. The integral cross sections of the four different quantum states decreased gradually with the increase of the collision energy. And the gap between them was more and more small, the impact of high-energy on cross section was large and the impact of lower energy was small. According to the results of reaction process, we found that the reaction changed from indirect reaction mechanism to direct one.Besides, we investigated the dynamics of the reaction with the different rotational quantum numbers. In the same collision energy of 0.2e V, the effects of alignment and orientation was small. Except the value of J = 0（ the collision energy was 0.1e V） was higher than other values, the values were almost consistent under the other conditions. Overall, rotational excitation effect on the reaction was not very obvious. Due to the characteristics of the reaction scattering asymmetry, the intermediate complex O–H–H⁺ formed at the four reactions which illustrated the reaction was dominated by the indirect mechanism.Finally, we studied the impact of the isotope effect on the reaction. The three reaction cross sections dropped with the increase of relative energy, but as H, D, T atomic mass increased, the absolute values of the integral reaction cross sections decreases, which was obviously due to the change of three reaction quality factors. The distributions of forward and backward scattering were asymmetric, which the degree of forward scattering was stronger than the backward scattering. Meanwhile, the reaction had a little sideward scattering.