Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

A theoretical study of the potential energy surface for O(3P)+H2

Abstract: Barrier heights and transition state geometries have been calculated for the reaction O(3P)+H2→OH+H using large scale POL‐CI wave functions (based on GVB wave functions using basis sets of up to triple zeta valence plus double zeta polarization quality). A detailed study was made of the effects on the calculated barrier height and saddle point geometry of (i) basis set, (ii) choice of orbitals, and (iii) choice of reference configurations. Calculations using a [4s3p2d/3s2p] basis lead to a collinear saddle point with rHH=0.92 A and rOH=1.23 A with a corresponding barrier height of 12.5 kcal/mole. There are two surfaces which connect the reactants with the products: one of 3A′ symmetry and one of 3A″ symmetry (these correspond to the two degenerate components of the 3Π state in collinear geometries). In the transition state region, the 3A′ surface has a steeper bending curve than the 3A″ surface leading to significantly different reaction rates on the two surfaces.

Theoretical studies of the HO + O HO2 H + O2 reaction. II. Classical trajectory calculations on an ab initio potential for temperatures between 300 and 5000 K.

Abstract: A comparably simple new analytical expression of the potential energy surface for the HO+O⇔HO2⇔H+O2 reaction system is designed on the basis of previous high precision ab initio calculations along the minimum energy path of the HO2→H+O2 and HO2→HO+O dissociations. Thermal rate constants for the reaction HO+O→H+O2 are determined by extensive classical trajectory calculations. The results depend on the policy to solve the zeropoint energy problem. We show that, with the chosen policy, there are nearly equal amounts of statistical and nonstatistical backdissociations HO+O←HO2 following HO+O→HO2; however, backdissociations become important only at temperatures above about 500 K. Below 500 K, the reaction is completely capture-controlled. Below 300 K, classical trajectory treatments become inadequate, because quantum effects then are so important that only the quantum statistical adiabatic channel model gives reliable results. For the reaction HO+O→H+O2 and the range 300–5000 K, a rate constant of k/10−11 cm3 molecule−1 s−1=0.026(T/1000 K)1.47+1.92(1000 K/T)0.46 is obtained from the trajectory calculations. Converting experimental results for the reaction H+O2→HO+O to the reverse reaction on the basis of the revised enthalpy of formation of OH, agreement between experiment and theory within better than 20% is obtained between 300 and 5000 K.

Exact quantum transition probabilities by the state path sum method: Collinear F + H2 reaction

Abstract: Exact quantum mechanical transition probabilities have been calculated for the collinear F + H2 →H + HF reaction by the State Path Sum method. The potential energy surface used is based on the ab initio SCF CI surface of Bender et al. For the energy range considered, four product channels are open. Pronounced level inversion is found. The dominant transition is the 3 ←0 one. It has a resonance-like energy dependence which is similar to that for the 2 ←0 transition. The 1 ←0 and 0 ←0 transition probabilities are negligible. These results are compared with those of Wu et al. and Schatz et al. who use semi-empirical LEPS surfaces.

Understanding hydrogen scrambling and infrared spectrum of bare CH5+ based on ab initio simulations

Abstract: A comprehensive study of the properties of protonated methane obtained from ab initio molecular dynamics simulations is presented. Comparing computed infrared spectra to the measured one gives further support to the high fluxionality of bare CH5+. The computational trick to partially freezing out large-amplitude motion, in particular hydrogen scrambling and internal rotation of the H2 moiety, leads to an understanding of the measured IR spectrum despite the underlying rapid hydrogen scrambling motion that interconverts dynamically structures of different symmetry and chemical bonding pattern. In particular, the fact that C–H stretching modes involving the carbon nucleus and those protons that form the H2 moiety and the CH3 tripod, respectively, result in distinct peaks is arguably experimental support for three-center two-electron bonding being operative at experimental conditions. It is proposed that hydrogen scrambling is associated with the softening of a mode that involves the bending of the H2 moiety relative to the CH3 tripod, which characterizes the Cs ground-state structure. The potential energy surface that is mapped on to a two dimensional subspace of internal coordinates provides insight into the dynamical mechanism for exchange of hydrogens between CH3 tripod and the three-center bonded H2 moiety that eventually leads to full hydrogen scrambling.