Avigdor Persky

Quasiclassical trajectory study of the reaction O(3P)+HCl → OH+Cl. The effects of vibrational excitation, rotational excitation, and isotopic substitution on the dynamics

Three dimensional quasiclassical trajectory calculations were carried out for the nearly thermoneutral reaction of oxygen atoms O(3P) with hydrogen chloride molecules (HCl and DC1), for reaction temperatures of 300 and 700 K, employing two LEPS potential energy surfaces. Calculations for 300 K were performed for various initial vibrational states of the reagents HCl(ν=0, 1, 2, and 4) and DC1(ν=0 and 1). Calculations for 700 K were carried out for the ground vibrational state ν=0. The effect of rotational excitation on reactivity was investigated by calculating reaction cross sections for specific initial rotational states for the reaction O+HCl(ν=0, J=0–19) for collision energies of 6.0 and 10.0 kcal/mol. The rate of the O+HCl reaction was found to be enhanced by more than two orders of magnitude (factors of 150 and 390 for the two surfaces used) for O+HCl(ν=1), and by more than three orders of magnitude for O+HCl(ν=2), as compared to O+HCl(ν=0). The influence of rotational excitation on reactivity was fo...

A three-dimensional quantum mechanical study of the F + H2/D2 reactions. On a new potential energy surface

Abstract We report quantum mechanical cross sections and rate constants for the title reactions, as calculated on the Stark-Werner potential energy surface. The calculations, carried out in the reagents arrangement channel by employing negative imaginary potentials, were done within the coupled-state approximation. The calculated cross sections were compared with quasi-classical trajectory calculations. The calculated rate constants for the two title reactions as well as their isotopic ratio were found to be in good agreement with experiment. Part of the study is devoted to showing the existence of strong tunneling processes caused by a thin potential barrier.

Quasiclassical trajectory study of the reaction O(3P)+H2→OH+H. The effects of the location of the potential energy barrier, vibrational excitation and isotopic substitution on the dynamics

Three dimensional quasiclassical trajectory calculations were carried out for the nearly thermoneutral reaction of oxygen atoms O(3P) with hydrogen molecules (H2,D2, and HD). Three LEPS potential energy surfaces, all having the same barrier height but with slightly different locations, were used for the calculations. Calculations for various initial vibrational states of H2 were performed for reaction temperatures of 300, 500, and 900 K. For the reactions O+D2 and O+HD calculations were carried out for the ground vibrational state for 500 and 900 K. The trajectory calculations showed that the rate constants are very sensitive to the position of the potential energy barrier. They increase or decrease considerably when the barrier is shifted slightly in the direction of the exit valley or entry valley, respectively. The rate of the reaction O+H2(υ)→OH+H was found to be enhanced significantly with vibrational excitation of the H2. At 300 K the rate constant for υ=1 was found to be larger than for υ=0 by thre...

The effect of reagent rotation on steric requirements of elementary exchange reactions

Abstract The body-fixed coordinate system appears to be particularly suited for discussing the role of reagent rotation. The simple picture provided by the jz-conserving approximation accords with the available evidence and with specially performed trajectory computations for the O + HCl(v= 0,j) and O + DCl(v= 0,j) reactions. An even simpler, Line-of-centers-type model is also discussed. Both the possible decline in reactivity at low rotational excitation and its increase at higher levels of excitation can be accounted for.

The kinetics of the reaction F + H2 HF + H. A critical review of literature data

Published experimental studies concerning the determination of rate constants for the reaction F + H2 HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10−10 exp |-(450 ± 50)/T| cm3 molecule−1 s−1, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10−11 cm3 molecule−1 s−1. The recommended Arrhenius expression for the reaction F + D2 DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10×10 exp |-(635 ± 55)/T|cm3 molecule−1 s−1, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10−11 cm3 molecule−1 s−1.

Quasiclassical trajectory study of the reaction O(3P) + HI → OH + I

Abstract Three-dimensional quasiclassical trajectory calculations were carried out for the reaction of oxygen atoms O( 3 P) with hydrogen iodide molecules (HI and DI) for the temperature range 200–550 K, using a LEPS potential-energy surface. The calculated results include reaction cross sections, rate constants, kinetic isotope effects, the influence of vibrational and rotational excitation of the reactants on the dynamics, and the product energy partitioning and angular distribution. The calculated results are in good agreement with the available experimental results. The dynamics of the O + HI reaction is discussed in view of the associated mass combination H + LH ′ ( H and H ′ are heavy atoms and L is a light atom), and in relation to earlier trajectory results for the reactions O + HCl and O + HBr.

The exoergic F+CH4 reaction as an example of peripheral dynamics

Abstract Classical trajectory computations for thermal reactants on a six-atom potential show a forward scattering component which is correlated with the HF product being formed with high vibrational excitation. These trajectories are peripheral collisions where the F atom approaches CH4 with a high impact parameter and reaction is through a nearly collinear F–H–C configuration with a stretched F–H bond. Other trajectories are well described by a hard-sphere model whose cutoff is below the range of peripheral collisions. Comparison is made with the F+H2 and other reactions where nearly thermoneutral channels correlate with forward scattering.

Dynamics of the reactions Cl+HBr→HCl+Br and Br+Hl→HBr+I. A quasiclassical trajectory study

Abstract Three-dimensional quasiclassical trajectory calculations using LEPS potential energy surfaces were carried out for the reactions Cl+HBr→HCl+Br and Br+HI→HBr+I, which belong to the heavy +light-heavy class of reactions. The results which include rate constants, kinetic isotope effects, the influence of vibrational and rotational excitation of the reactants on reaction cross sections, and product energy distributions, are compared with available experimental data and discussed in relation to the heavy+light-heavy mass combination.

Correlations between dynamical properties and features of potential energy surfaces for the light atom transfer reactions O+HCl→OH+Cl AND Cl+HCl→ClH+Cl

Abstract A three-dimensional quasiclassical trajectory study of the dynamics of the light atom transfer reaction O( 3 P) + HCl(ν=0)→ OH + Cl was carried out employing two LEPS potential energy surfaces (I and II). Attention was focused mainly on three-dynamical properties; the oscillatory behavior of partial cross sections as a function of collision energy; the rotational excitation of the products; and the influence of reagent rotation on reactivity. Distinct differences were found between surfaces I and II with respect to these properties. The examination of individual trajectories indicated that there is a significant difference in the nature of these surfaces. While surface I is governed by weak repulsive forces, surface II is governed by strong attractive forces which tend to direct the reactants toward a collinear geometry. The present results confirm conclusions reached from an earlier study of the reaction Cl+HCl→ClH+Cl concerning correlations between dynamical properties and features of potential energy surfaces. For surfaces of the type that we termed HREP, since they are of rep ulsive nature and they lead to h ighly rotationally e xcited p roducts, no significant oscillations of partial cross sections are obtained and reagent rotation promotes the reaction. On the other hand, for surfaces of the type that we termed COLD ( col linearly d irecting), since they tend to direct the reactants toward a collinear geometry and form rotationally “ cold ” products, significant oscillations of partial cross sections are obtained and reagent rotation causes a decline in reactivity.

Quasiclassical trajectory studies of the chlorine–hydrogen system. I. Cl+H2→HCl+H

Detailed three‐dimensional quasiclassical trajectory calculations were performed for the reaction Cl+H2(0,J) →HCl+H on a semiempirical LEPS potential energy surface. Calculations were carried out for initial vibrational state v=0, rotational states J=0–4, and collision energies E between threshold and 12.0 kcal/mole. From the trajectory calculations we obtained reaction probabilities Pr(v=0,J,E,b) as a function of impact parameter b and initial values of J and E; reaction cross sections Sr(v=0,J,E) as a function of initial J and E; detailed rate constants k0,J and total rate constants kt in the temperature range 250–600°K, and the partitioning of energy and angular distribution of the products for different initial conditions. Thermal rate constants were compared with results of other trajectory studies of this system, with results of transition state theory calculations, and with experimental results. The trajectory rate constants of the present study were found to be in good agreement with experimental ...