Global nine-dimensional potential energy surface for the H5 system. II. Fit to an analytical expression

Phys. Chem. Chem. Phys.

2018

Self Cite

Is the rise of the rate constant measured in laval expansion experiments of OH with organic molecules at low temperatures due to the reaction between reactants or to the formation of complexes with the buffer gas?. This question has importance for understanding the evolution of prebiotic molecules observed in different astrophysical objects. Among these molecules methanol is one of the most widely observed, and its reaction with OH has been measured by several groups showing a fast increase of the rate constant under 100K. Transition state theory doesn’t reproduce this behavior and here dynamical calculations are performed on a new full dimensional potential energy surface developed for this purpose. The calculated classical reactive cross sections show an increase at low collision energies due to a complex forming mechanism. However, the calculated rate constant at temperatures below 100 K remains lower than the observed one. Quantum effects are likely responsible for the measured behavior at low temperatures.

Section: Ab Initio Calculations and Analytical Pesmentioning

confidence: 99%

Low temperature reaction dynamics for CH₃OH + OH collisions on a new full dimensional potential energy surface

Roncero

Zanchet

Phys. Chem. Chem. Phys.

2018

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“…For describing the ground electronic state, a diagonal matrix with all elements being equal. This matrix element is expanded in terms of permutationaly invariant polynomials38,39, as in the method of Bowman et al 29. In this case, the RFF does not have all permutation symmetry, but only the physically allowed by energy, i.e.…”

Section: Potential Energy Surfacementioning

confidence: 99%

Full dimensional potential energy surface and low temperature dynamics of the H₂CO + OH → HCO + H₂O reaction

Zanchet

Mazo

Phys. Chem. Chem. Phys.

et al. 2018

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A new method is proposed to analytically represent the potential energy surface of reactions involving polyatomic molecules capable of accurately describing long-range interactions and saddle points, needed to describe low-temperature collisions. It is based on two terms, a reactive force field term and a many-body term. The reactive force field term accurately describes the fragments, long-range interactions among them and the saddle points for reactions. The many-body term increases the desired accuracy everywhere else. This method has been applied to the OH + HCO → HO + HCO reaction, giving a barrier of 27.4 meV. The simulated classical rate constants with this potential are in good agreement with recent experimental results [Ocaña et al., Astrophys. J., 2017, submitted], showing an important increase at temperatures below 100 K. The reaction mechanism is analyzed in detail here, and explains the observed behavior at low energy by the formation of long-lived collision complexes, with roaming trajectories, with a capture observed for very long impact parameters, >100 a.u., determined by the long-range dipole-dipole interaction.

“…Section II is devoted to describe the ab initio calculations, the DIM and TRIM treatments, and the fitting procedure followed to include the five-body correction terms, considering the full permutation symmetry of the system. 40 Section III presents the results and compares them with previously proposed PES for this system. Finally, in Sec.…”

Section: Hmentioning

confidence: 99%

“…The fivebody terms V 5B are treated following the method developed for the description of H 5 . 40 The H 2 +H 3 + asymptote is well reproduced by the TRIM method, and the H + H 4 + asymptote is about 100 kcal/mol higher in energy, 47 so it will not be considered here. For this reason, in Eq.…”

Section: Global Pes Fittingmentioning

confidence: 99%

“…͑16͒ the sum is done taking into account some constraints such as i + j + k +¯+t Յ M, as well as additional ones to ensure that the five-body term does not contain lower order contributions. 40 Finally, the d ijk¯t linear coefficients of the expansion are determined, as described previously, 52 by minimizing the difference between the global potential, in Eq. ͑15͒, and the calculated ab initio CCSD͑T͒/cc-pVQZ points.…”

Section: Global Pes Fittingmentioning

confidence: 99%

See 1 more Smart Citation

A new accurate and full dimensional potential energy surface of H5+ based on a triatomics-in-molecules analytic functional form

The Journal of Chemical Physics

Barragán

Prosmiti

et al. 2010

163

In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H(5)(+) is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H(2) fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110,000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces.