Ernesto Garcia

The largest angle generalization of the rotating bond order potential: Three different atom reactions

The LAGROBO functional representation of the atom-diatom interaction has been extended to the case of three different atom reactive systems having two open product channels and an atom in an electronically excited state. The analytic formulation of the LAGROBO model is given and its application to the construction of the potential energy surface of the Li+FH and O(1D)+HCl reactions are discussed. Reactive properties calculated on these surfaces using quasiclassical methods are compared with experimental findings.

An improvement of the Li+HF PES based on a 3D quasiclassical trajectory test

A quasiclassical trajectory test of some potential energy surfaces designed for the Li+HF reaction is reported. A comparison of scattering quantities with experimental data has allowed the selection of a surface sufficiently accurate for reproducing reactive cross sections and detailed experimental data.

A bond-order LiFH potential energy surface for 3D quantum-mechanical calculations

Abstract A new fit to ab initio estimates of the LiFH potential energy has been obtained for use in a full three-dimensional quantum-mechanical calculation of the reactivity of this system.

Improved infinite order sudden cross sections for the Li+HF reaction

Reactivity of the Li+HF system has been calculated by adapting a light–heavy–light infinite order sudden computational scheme. The improvement of the numerical procedure as well as the restructuring of the computational code for use on supercomputers has allowed a successful extended comparison of calculated vs measured cross sections.

The largest angle generalization of the rotating bond order potential: The H+H2 and N+N2 reactions

A generalization of the rotating bond order model potential is discussed. The new functional representation is used for fitting the ab initio potential energy values of the H+H2 system and the main features of a LEPS potential energy surface for the N+N2 system. For H+H2 we analyze the accuracy obtained when fitting the ab initio potential energy values using different functional representations. For N+N2 we examine the deviation of some dynamic and kinetic properties calculated on the new model potential from those obtained from the original LEPS.

Potential energy representations in the bond order space

Abstract Different types of reaction channel coordinates defined in the bond order space are formulated. Their use for describing the interaction of reactive processes is also discussed.

A potential energy surface for the Li+HCl reaction

The potential energy surface for the Li+HCl reaction has been calculated by performing UHF/CI ab initio computations for a large number of molecular geometries. To make the surface suitable for dynamical studies, the analytical interpolation of the CI points has been performed using a multi‐body expansion of the potential and bond order variables with constraints on diatom asymptotic and transition state energies. To test the quality of the potential surface an investigation of its dynamical properties has been carried out using quasiclassical trajectories. Calculated scattering quantities have been compared to experiment.

Can quasiclassical trajectory calculations reproduce the extreme kinetic isotope effect observed in the muonic isotopologues of the H + H2 reaction?

Rate coefficients for the mass extreme isotopologues of the H + H(2) reaction, namely, Mu + H(2), where Mu is muonium, and Heμ + H(2), where Heμ is a He atom in which one of the electrons has been replaced by a negative muon, have been calculated in the 200-1000 K temperature range by means of accurate quantum mechanical (QM) and quasiclassical trajectory (QCT) calculations and compared with the experimental and theoretical results recently reported by Fleming et al. [Science 331, 448 (2011)]. The QCT calculations can reproduce the experimental and QM rate coefficients and kinetic isotope effect (KIE), k(Mu)(T)/k(Heμ)(T), if the Gaussian binning procedure (QCT-GB)--weighting the trajectories according to their proximity to the right quantal vibrational action--is applied. The analysis of the results shows that the large zero point energy of the MuH product is the key factor for the large KIE observed.

Ab initio calculations and dynamical tests of a potential energy surface for the Na+FH reaction

Ab initio calculations of the potential energy surface for the ground state Na+FH reaction were performed. Calculated potential energy values were fitted using a polynomial in bond order coordinates. Quasiclassical trajectories integrated on the fitted surface were used to calculate reactive properties of the system. Calculated quasiclassical properties agree with available experimental information. Quasiclassical trajectories allowed also a rationalization of the reactive dynamics of the system.

A LAGROBO strategy to fit potential energy surfaces: the OH + HCl reaction

The LAGROBO functional formulation of the interaction for four atom reactions is revisited and a strategy to fit the potential energy surface of the OH + HCl reaction to measured rate coefficients is discussed. The flexibility of the LAGROBO functional has allowed to keep the changes highly localized and to estimate the effect of varying the height of the barrier to reaction on the value of the related rate coefficients. An interesting agreement with the low temperature data is also found.