Miquel Gilibert

Dynamics of the N(4Su) + NO(X 2Π) → N2(X 1Σg+) + O(3Pg) atmospheric reaction on the 3A‘ ground potential energy surface. I. Analytical potential energy surface and preliminary quasiclassical trajectory calculations

The N(4Su)+NO(X 2Π)→N2(X 1Σg+)+O(3Pg) reaction plays an important role in the upper atmosphere chemistry and as a calibration system for discharge flow systems. Surprisingly, very little theoretical and experimental work has been devoted to the characterization of the dynamical features of this system. In this work a Sorbie–Murrell expression for the lowest 3A‘ potential energy surface (PES) connecting reactants in their ground electronic states based upon the fitting of an accurate ab initio CI grid of points has been derived. The PES fitted shows no barrier to reaction with respect to the reactants asymptote in accordance with experimental findings and becomes highly repulsive as the NNO angle is varied away from the saddle point geometry. The results of preliminary quasiclassical trajectory calculations on this surface reproduce very well the experimental energy disposal in products, even though the vibrational distribution derived from trajectories seems to be a bit cooler than the experimental data. ...

A THREE-DIMENSIONAL QUANTUM MECHANICAL STUDY OF THE H+H2+ H2+H+ SYSTEM : COMPETITION BETWEEN CHEMICAL EXCHANGE AND INELASTIC PROCESSES

In this publication is presented a three-dimensional quantum mechanical study, within the coupled states approximation, of the process H+H2+(v1=0,j1)→H++H2. Both reactive (exchange) and inelastic processes were considered. The main findings are: (a) The charge transfer process takes place at large distances (∼3.5 A) and so the reagents are essentially on the lower potential energy surface when they approach the close interaction region; (b) The main contributions to the reaction (exchange) are from large impact parameters; (c) The initial rotational states have at most a minor effect on the results (whether being charge transfer or chemical exchange); (d) The deep potential well in the interaction region of the lower surface has only a secondary effect on the results.

Quasiclassical trajectory study of the N(4Su) + O2 (X 3Σ−g)→NO (X 2Π) + O (3Pg) atmospheric reaction on the 2A′ ground potential energy surface employing an analytical Sorbie—Murrell potential

Abstract The reaction between ground state nitrogen atoms and oxygen molecules plays an important role in the chemistry of the upper atmosphere as a source of infrared chemiluminescence and also as a participant in the auroral mechanism. Even though there is considerable experimental stock concerning rate constants over a wide range of temperatures and also on the vibrational distribution of products, as well as theoretical information about the potential energy surfaces of this system, no extensive work is available on its dynamical features. The present paper is concerned with the construction of an analytical Sorbie—Murrell surface for the lowest 2 A′ surface correlating reactants and products in their ground electronic states, based upon the reproduction of a grid of ab initio CI points and a preliminary dynamics on that surface. The analytical potential energy surface fits the corrected ab initio CI barrier of 7.6 kcal/mol, in agreement with the experimental estimates, exhibiting also a repulsive behaviour of the NOO bending at the saddle point configuration. Quasiclassical trajectories lead on the whole to a rather good reproduction of the different experimental properties measured. The calculated vibrational distribution resulting from the present QCT calculations does not however fully agree with any of the existing experimental, mutually conflicting, measurements.

A comparison between experimental, quantum and quasiclassical properties for the N(4S) + O2 (X3Σg) → NO (X2Π) + O(3P) reaction

Abstract A detailed reactive infinite order sudden approximation (R-IOSA) study of the reactivity of the N ( 4 S ) + O 2 system has been carried out in the 0.53–1.5 eV translational energy range. Results have been compared with experimental and quasiclassical trajectory (QCT) data. The general dynamical features already obtained within the QCT framework have been reproduced. In addition, the R-IOSA product vibrational distribution matches almost quantitatively the experimental one. The relative importance of the different ν′ contributions, both to the classical and quantum more averaged quantities has been interpreted with the help of the state-to-state opacity function. Finally, the alternating vibrational distribution and its evolution with translational energy are discussed within the context of a Franck-Condon type model.

Accurate 3 dimensional quantum dynamical study of the Ne+H2+→NeH++H reaction

In this work a comprehensive, fully converged coupled states (CS) quantum mechanical (QM) study of the endothermic Ne+H2+ ion-molecule reaction is presented. The computed dynamical properties are compared with quasi-classical trajectory (QCT) and with the available experimental data. To this end, the analytical potential energy surface of Pendergast, Heck, Hayes, and Jacquet was employed. The two main features of the dynamical behavior for this system are: (1) the rich structure present in the state-selected integral cross section energy-dependent curves, which may be attributed to resonances surviving the partial wave summation; and (2) the large differences between the quantum and the QCT cross sections which are caused by the inability of classical mechanics to conserve the zero point energy. Also noteworthy are the strong enhancement of the reactivity due to higher vibrational states and the effect of the activated complex, formed during the reaction process, on the angular and the rotational distribu...

Dynamics of the O+(4S)+H2(X 1Σg+)→OH+ + H Ion-molecule reaction and some of its isotopic variants (D2 and HD). II. Quasiclassical trajectory study in the range of relative energies 0.25–6.30 eV

Abstract The reaction dynamics of the O+(4S)+H2 system and several isotopes (D2 and HD) have been investigated following the quasiclassical trajectory approach, employing a LEPS + IDI empirical surface derived by us previously from experimental and ab initio information. The properties analysed can be adequately interpreted on the basis of the main topological features of the potential energy surface (PES) used, and comparison of theoretical results with experimental data shows quite good accord, with the only exception of the total cross sections at relative energies above 1 eV which are higher than the experimental ones. Because of the approximate nature of the calculations quantitative agreement with the experiment should not be expected. However, this single surface treatment of the O++H2 reaction dynamics leads to reasonably good agreement with the experimental information available.

Variational transition state calculation of the rate constants for the N(4Su)+O2(X 3Σg−)→NO(X 2Π)+O(3Pg) reaction and its reverse between 300 and 5000 K

Abstract An improved analytical fit of the ground (2A′) potential energy surface (PES) involved in the N+O 2 →NO+O reaction and its reverse has been derived. This PES leads to variational transition state theory (VTST) rate constants that are in agreement with the experimental data of both reactions. The substantial improvement achieved for the forward reaction suggests that the new analytical PES should be more adequate than the earlier ones to describe this system.

Dynamics of the N(4S)+NO(X 2Π)→N2(X 1Σ+g)+O(3P) atmospheric reaction on the 3A″ ground potential energy surface. III. Quantum dynamical study and comparison with quasiclassical and experimental results

A detailed reactive–infinite‐order sudden approximation (R‐IOSA) study of the reactivity of the N+NO→N2+O system has been carried out in the 0.0038 to 1.388 eV translational energy range and the results have been compared with the existing quasiclassical trajectory (QCT) and experimental data available. The general features already observed in the previous QCT studies are reproduced qualitatively in the quantum study, even though some differences arise in the product vibrational distributions and state‐to‐state opacity functions in the low energy range. The observed differences have been justified in terms of the anisotropy of the potential energy surface and the vibrational barriers to reaction at fixed angles. A strong vibrational adiabaticity is observed quantally in the low translational energy range, disappearing at moderately high collision energies (around 0.3 eV), where a simple Franck–Condon type model is capable of describing the evolution of the vibrational distribution with translational energ...

Dynamics of the N(4Su)+NO(X 2Π)→N2(X 1Σ+g)+O(3Pg) atmospheric reaction on the 3A‘ ground potential energy surface. II. The effect of reagent translational, vibrational, and rotational energies

The effect of translational vibrational, and rotational energies on the dynamics of the N(4Su)+NO(X 2Π)→N2(X 1Σg+)+O(3Pg) reaction has been examined using a Sorbie–Murrell analytical fitting of a grid of ab initio configuration interaction (CI) points for the 3A‘ ground potential energy surface reported by the authors in a previous work. Translational energy is shown to increase total reaction cross section for all the initial rovibrational states of reactants considered. The reaction mode analysis points towards a direct mechanism and a strong influence of the shape of the potential energy surface on the reactivity, especially at low relative collision energies. Vibrational excitation of the NO reactant molecule changes the total reaction cross section values moderately, while increasing the initial rotational states of NO at low fixed relative collision energies decreases the reaction cross section sharply, eventually becoming zero for the highest J values explored. By comparing with model calculations ...

Dynamics of the O+(4S)+H2(X 1Σg+)→OH+ + H ion-molecule reaction and some of its isotopic variants (D2 and HD). I. Potential energy surface and preliminary quasiclassical trajectory analysis

Abstract This work discusses by means of a single surface model based on a quasiclassical trajectory approach the suitability of some LEPS + IDI empirical surfaces, derived from experimental results and ab initio calculations, to reproduce the dynamics of the ion-molecule reaction O + ( 4 S)+H 2 →OH + +H and some of its isotopic variants (D 2 and HD). For this system, we have shown that it is possible to construct a LEPS+IDI surface which reasonably describes all available experimental data at low and moderate collision energies (1.0⩽ E R ⩽6.3 eV).