A Full-dimensional Potential Energy Surface Of The Multichannel Reaction Between H And HO₂ And Its Dynamics

Molecular Reaction Dynamics is an important subject for studying the elementary process of chemical reactions by analyzing the movement and interaction of each particle with atoms and molecules as the research object,so it is also called Microscopic Chemical Kinetics.The core content of the theoretical research on the kinetics of polyatomic reactions is mainly to construct the potential energy surface and study the kinetic properties.By constructing a high-precision potential energy surface and solving the Schr?dinger equation of atomic nucleus motion,various kinetic information of the corresponding reaction system can be obtained,such as reaction probability,branch ratio,integral cross section and differential cross section.Therefore,it can be seen that the construction of accurate and reliable potential energy is particularly important for the theoretical study of molecular reaction kinetics,which is the prerequisite for us to correctly understand the mechanism of chemical reactions.As a typical multi-channel reaction system,the hydrogen atoms（H）and hydroperoxyl radicals（HO₂）play significant roles in atmospheric,combustion and interstellar chemistry.Based on the ab initio method of MRCI+Q-F12/CVDZ-F12,the electron energies of about 30500 structures were calculated,and the full dimensional potential energy surface of the lowest triplet state of H+HO₂ reaction system was constructed by using permutationally invariant polynomials–neural network（PIP-NN）fitting method.This potential energy surface covers four reaction channels including H₂+O₂,OH+OH,O+H₂O and exchange H channel.Based on this full-dimensional high-precision potential energy surface,the quasi-classical trajectory（QCT）approach was then carried out to study the reaction dynamical properties.The reactivity and branching ratio of each reaction channel were studied at the collision energy of 2,5,10,15,20,25,and 30 kcal/mol.At the collision energy of 20 kcal/mol,the distributions of the product energies,ro-vibrational states,and the scattering angle for the H₂+O₂channel with the largest reactivity were computed.For the energy distribution of products,compared with the commonly used histogram,we also use fixed bandwidth and variable bandwidth kernel density estimation（KDE）methods for statistics and comparison.In statistical distribution,histogram is greatly affected by bandwidth selection and sample distribution,so these two factors will affect the distribution characteristics of the samples.The kernel density estimation method can effectively avoid these problems.Generally,the results obtained from the analysis of several sets of energy data by these three methods are relatively consistent.But when the sample distribution is uneven,the histogram and fixed bandwidth kernel density estimation method usually use a smaller bandwidth to describe the data in the entire range.Therefore,in order to avoid undersmooth distribution,it is better to choose kernel density estimation with variable bandwidth.