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The potential energy surfaces (PES) of deuterium compounds studied using quasiclassical trajectory (QCT) and quantum mechanics (QM) methods are presented. PES correlates with ground state reagents and not with ground state products and undergo nonadiabatic transitions. The product translational energy distributions of the compounds were also carried out using molecular beam experiments.

The H+D2(v = 0, j = 0)→HD(v′, j′)+D isotopic variant of the hydrogen atom exchange reaction has been studied in a crossed molecular beam experiment at a collision energy of 2.20 eV. Kinetic energy spectra of the nascent D atoms were obtained by using the Rydberg atom time-of-flight technique. The extensive set of spectra collected has permitted the derivation of rovibrationally state-resolved differential cross sections in the center-of-mass frame for most of the internal states of the HD product molecules, allowing a direct comparison with theoretical predictions. Accurate 3D quantum mechanical calculations have been carried out on the refined version of the latest Boothroyd-Keogh-Martin-Peterson potential energy surface, yielding an excellent agreement with the experimentally determined differential cross sections. The comparison of the results from quasi-classical trajectory calculations on the same potential surface reveals some discrepancies with the measured data, but shows a good global accordance. The theoretical calculations demonstrate that, at this energy, reactive encounters are predominantly noncollinear and that collinear collisions lead mostly to nonreactive recrossing. The experimental results are satisfactorily accounted for by theoretical calculations without consideration of Geometric Phase effects. © 1999 American Institute of Physics.

Scattering measurements performed at an energy slightly higher than that of the lowest crossing between the ground and the first electronically excited state of the H3 system are reported. The essentials of the reactive dynamics are describable in terms of a classical motion of the nuclei on the lowest adiabatic electronic potential. © 1997 American Institute of Physics.

The quasiclassical trajectory method has been applied to the calculation of cross sections and rate constants for the H + D2 → HD +D reaction on three ab initio potential energy surfaces. The results include state-selected cross sections for the reaction with D2(v=0 j=0-9) and D2(v=1 j=0) and thermal rate constants in the 200-1500 K temperature range. A global good agreement is found between the present results and those from experiment and from approximate quantum mechanical calculations. This agreement is particularly good between 200 and 900 K. At higher temperatures, the quasiclassical rate constants deviate gradually toward lower values. A detailed comparison is performed between the reactivity of this isotopic variant and that of D + H2. Special attention is paid to the effect of rotational excitation on reactivity, which is opposite for the two isotopomers, and to the microscopic dynamics responsible for the observed ratio of thermal rate constants and cross sections. In particular, the larger reaction cross section of D + H2 as compared with H + D2 is found to be caused by the more efficient transfer of collision energy from the heavier D atom to the molecular bond of the lighter H2 molecule. These findings can be rationalized with simple dynamical models.© 1997 American Chemical Society

The reactivity of H + D2(v = 0, j = 0) → HD(v1, j1) + D has been investigated in a high resolution crossed molecular beam experiment at a collision energy of 2.2 eV. Time-of-flight (TOF) spectra of D atoms at different laboratory (LAB) scattering angles and their total angular distribution were measured using the technique of Rydberg atom TOP spectroscopy. The resolution of this technique allows the identification of individual rovibrational states of the corresponding HD product molecule at the different LAB angles. A detailed simulation of the experimental measurements has been performed by using state resolved differential cross sections from quasiclassical trajectory (QCT) calculations on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) and on the double-many-body-expansion (DMBE) potential energy surfaces (PES). A general good agreement between experiment and theory is found, although there are some discrepancies which are discussed.

Reaction cross sections and rate constants for the D + H2(v = 0-1, j = 0-7) reaction have been obtained by quasi-classical trajectory (QCT) calculations on the three ab initio potential energy surfaces (PESs) available for this system. A good agreement has been found between the QCT and quantum mechanical (QM) reaction cross sections and rate constants for the D + H2(v = 0-1, j = 0) reactions. Thermal rate constants for the D + n-H2(v=0) and D + n-H2(v=1) have been calculated from the excitation functions, over a wide range of temperatures. The comparison with the quantum mechanical (QM) calculations and experimental results shows that, in general, QCT thermal rate constants are smaller than their QM and experimental counterparts, and this can be traced back to a decrease in the classical reactivity in the threshold region with rotational excitation of the reagents. In addition, the analysis of the QCT results provides an explanation for the differences found in thermal rate constants calculated on the three PESs in terms of specific features of each of these potentials. © 1996 American Chemical Society.

Reaction cross sections and rate constants for the F + HD reaction have been calculated on the recently released Stark-Werner (SW) ab initio potential energy surface (PES) using the quasiclassical trajectory (QCT) method. The results are compared to other theoretical calculations on different PESs and to experimental isotopic branching ratios. The general agreement is good. Dynamical features related to the asymmetric nature of the HD molecule are also discussed.© 1996 Elsevier B.V.

The dynamics of the F+HD reaction has been studied by means of quasiclassical trajectory calculations on an ab initio potential energy surface (PES) at several collision energies. At the collision energy of 85.9 meV and for the DF+H isotopic channel of the reaction, there is a remarkable agreement between calculated and experimental results, in both the center of mass (c.m.) differential cross sections (DCS) and in the simulation of the laboratory (LAB) time of flight (TOF) and angular distributions (AD). The good agreement also extends to the lower collision energy of 58.6 meV for this channel of the reaction. In contrast, the simulation of the LAB angular distributions for the HF+D channel shows strong discrepancies between theory and experiment at both collision energies, which can be traced back to the absence of a forward peak in the calculated cm. DCS for HF(v′=3). Simulations made from QCT calculations on other PES with important HF(v′=3) forward scattering contributions also fail to reproduce the overall AD. The theoretical findings and especially the roles of translational energy and initial rotational momentum on the dynamics of this reaction are discussed in terms of the topology of the PES through the analysis of individual trajectories. © 1995 American Institute of Physics.

The H + H2 exchange reaction constitutes an excellent benchmark with which to test dynamical theories against experiments. The H + D2 (vibrational quantum number v = 0, rotational quantum number j = 0) reaction has been studied in crossed molecular beams at a collision energy of 1.28 electron volts, with the use of the technique of Rydberg atom time-of-flight spectroscopy. The experimental resolution achieved permits the determination of fully rovibrational state-resolved differential cross sections. The high-resolution data allow a detailed assessment of the applicability and quality of quasi-classical trajectory (QCT) and quantum mechanical (QM) calculations. The experimental results are in excellent agreement with the QM results and in slightly worse agreement with the QCT results. This theoretical reproduction of the experimental data was achieved without explicit consideration of geometric phase effects.

A detailed comparison of quasiclassical trajectory (QCT) and quantum mechanical (QM) reaction probabilities and differential cross sections for the H+D2→HD+D reaction at the collision energies of 0.54 and 1.29 eV has been carried out using the same potential energy surface. The theoretical simulation of the recently published experimental results is also reported. The comparisons made here demonstrate the level of agreement between QCT and QM approaches, as well as between theory and experiment for this reaction. © 1994 American Institute of Physics.

State-resolved integral and differential cross sections have been calculated for the F + H2 (v = 0) → HF + H reaction by using the method of quasiclassical trajectories (QCT). The trajectories were run on the two latest versions (5SEC and 6SEC) of a partly ab initio potential energy surface. Dynamical calculations using the 6SEC surface yield branching ratios for the production of the various HF vibrational states in better agreement with experiment than those using the 5SEC one. Although the classical differential cross sections on the 6SEC surface are similar in shape to the ones obtained from accurate quantum mechanical (QM) calculations, significant differences are observed in the absolute values for the reaction with H2 (j = 0), as well as in the magnitude of the forward peak, especially at the highest collision energy studied. As the initial rotational quantum number increases to j = 1 and 2 at a fixed total energy the agreement between QM and QCT results improves. ©1994 Elsevier Science B.V