María Luz Hernández

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 detailed study of the dynamics of the O(1D)+HCl→OH+Cl, ClO+H reactions

A detailed and comprehensive study of the dynamics has been performed using quasiclassical trajectory calculations on a recent version of the ground 1 1A′ potential energy surface (PES) [M. T. Martinez et al., Phys. Chem. Chem. Phys. 2, 589 (2000)] for this system. This PES was shown to account very well for the various experimental results available for the HOCl system. It has been found that this reaction occurs following different mechanisms depending on whether the HClO, HOCl, or both wells are visited in the course of the reaction. The different scalar and vector properties are strongly dependent on the type of mechanism through which a reaction takes place. Calculations have also been carried out to determine the distribution of collision times for each of the different mechanisms, and the time evolution of the differential cross section. For both reaction chemical channels the backward scattering is delayed with respect to the appearance of forward scattering. Although this reaction has been consi...

Double-well structure and microscopic branching in the O(1D)+HCl reaction

Abstract By performing a quasiclassical trajectory study, we have confirmed that the title reaction can take place via different paths even when leading to the same product (microscopic branching). However, contrary to a previous hypothesis, no collinear collisions were found to contribute to the reaction. Therefore, the backward–forward structure of the ClO product angular distribution obtained in the crossed-beam experiment has to be ascribed to the combination of a backward peak associated with insertion-like collisions and a forward peak associated with side attachment of O on Cl. Proper combinations of insertion and attachment contributions also rationalize other properties of the title reaction.

An ab initio study of the O(1D)+HCl reaction

The potential energy surface of the O(1D)+HCl reaction has been calculated at an ab initio level. The calculated values have been fitted using a bond‐order polynomial. On this potential energy surface quasiclassical trajectory calculations have been performed. These calculations reproduce most of the available experimental information better than the other existing potential energy surfaces.

Quasiclassical trajectory simulation of the O(1D)+HCl→OH+Cl, ClO+H reactions on an improved potential energy surface

The CASSCF (complete active space self-consistent field) and MRCI (multi-reference configuration interaction) ab initio points of Hernandez et al. (J. Chem. Phys., 1996, 105, 2710) have been supplemented with new calculations of the same level of theory at selected geometries, and the whole set was used to fit an improved ground (11A′) potential energy surface (PES) for the O(1D)+HCl system. The points were fitted by a polynomial expansion in bond order coordinates, and the electronic excitation of the isolated oxygen atom was taken care of by a proper, smooth lowering of the HCl potential at long internuclear distances. This ensures a common dissociation to all ground state atoms. On the fitted surface quasiclassical trajectories have been run under conditions similar to those of the experiment. A very good agreement with beam data of Balucani et al. (Chem. Phys. Lett., 1991, 180, 34) was found for the LAB (laboratory frame) angular distribution and the time-of-flight spectra of ClO. A good agreement with the infrared chemiluminescence and laser induced fluorescence data of Kruus et al. (J. Chem. Phys., 1988, 88, 985) was found for the inverted vibrational distribution of the OH product.

“Anomalous” effect of the initial atom-diatom orientation on the Li + HF(v,J)→LiF + H reaction

Abstract Quasiclassical trajectory calculations have been performed on the Chen-Schaefer-Carter-Murrell potential energy surface of the title reaction at relative translational energies (T) of 15, 20 and 25 kcal.mol −1 with v=0,1 and 2 and J=0,1,2 and 7. The initial atom-diatom orientation (θ) shows a noteworthy effect on the reaction probability when v=J=O, namely the attack of the Li atom by the H-end cone of the HF molecule is favoured over the attack by the F-end cone in spite of being LiF the reaction product. The effect disappears for v=1 or 2. It is suggested that the necessity of a T-V energy transfer might explain the calculated effect.

Competing mechanisms and products' properties for the Be+HF reaction

Reactive properties of the Be+HF reaction have been investigated theoretically using a new fit of the ab initio potential energy values. The dependency of the reactive dynamics upon both the partition of the initial energy among the various diatomic degrees of freedom and the features of the potential energy surface is analyzed by discussing the structure of detailed products’ properties and the evolution of the reactive cross section with collision energy. Dynamical properties of competing reaction paths are also investigated by carrying out a detailed examination of selected trajectory plots.

Tutorial on Fitting of Potential Energy Surfaces

In this paper we present a tutorial on fitting of potential energy surfaces that was given at the I European Computational Chemistry School on Molecular and Reaction Dynamics. The tutorial consists in four exercises that involve the use of a computer running under UNIX operating system, programs and subroutines for assembling and analyzing potential energy surfaces, numerical methods for fitting and graphical tools for the visualization of results. This paper explains the background of the exercises and guides the reader to the succesful completion of the exercises.

Anabinitiostudy of the O(1D)+HCl reaction

The potential energy surface of the O(1D)+HCl reaction has been calculated at an ab initio level. The calculated values have been fitted using a bond‐order polynomial. On this potential energy surface quasiclassical trajectory calculations have been performed. These calculations reproduce most of the available experimental information better than the other existing potential energy surfaces.

An abinitio study of the O(1D)+HCl reaction

The potential energy surface of the O(1D)+HCl reaction has been calculated at an ab initio level. The calculated values have been fitted using a bond‐order polynomial. On this potential energy surface quasiclassical trajectory calculations have been performed. These calculations reproduce most of the available experimental information better than the other existing potential energy surfaces.