Dependence of Calculated Product Rotational Polarizations on the Scattering Angle for the O(1D) + HCl Reaction

Theoretical study of product polarization of O(1D) + HCl(v = 0; j = 0) → ClO + H and its isotope exchange reaction

O(1D) + HCl(v = 0; j = 0) → ClO + H and its isotope exchange reaction O(1D) + DCl(v = 0; j = 0) → ClO + D are studied in the collision energy range 14.0–20.0 kcal/mol based on the potential energy surface 1[Formula: see text] state. Reaction probabilities, integral cross sections, the two angular distribution functions (concerning the initial/final velocity vector, and the product rotational momentum vector), and the product rotational alignment parameters are calculated as a function of the collision energy for the two reactions. The four generalized polarization dependent differential cross sections are presented to manifest the polarization characters. Also, the effect of the collision energy and the kinetic isotope effect are studied.

The dynamical study of O(1D) + HCl(v = 0, j = 0) reaction at hyperthermal collision energies

Backgrounds

The quasi-classical trajectory calculations for O(¹D) + HCl → OH + Cl (R1) and O(¹D) + HCl → ClO + H (R2) reactions have been performed at hyperthermal collision energies (60.0, 90.0, and 120.0 kal/mol) on the ¹A' state. Reaction probabilities and integral cross sections are calculated. The product rotational distributions for the two channels, and the product rotational alignment parameters are investigated. Also, the alignment and the orientation of the products have been predicted through the angular distribution functions (concerning the initial/final velocity vector, and the product rotational angular momentum vector). To have a deeper understanding of the natures of the vector correlation between reagent and product relative velocities, a natural generalization of the differential cross section __PDDCS₀₀, is calculated.

Results

The OH + Cl channel is the main product channel and is observed to have essentially isotropic rotational distributions. The ClO + H channel is found to be clearly rotationally polarized.

Conclusions

The dynamical, especially the stereodynamical characters are quite different for the two channels of the title reaction. Most reactions occur directly, except for R2 reaction at the collision energies of 60.0 and 120.0 kcal/mol. The alignment and orientation effects are weak/strong for R1/R2 reaction. The well structure on the potential energy surface and hyperthermal collision energies might result in the dynamical effects.

CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM II

Using the accurate global potential energy surfaces for the 11A′, 11A′′, and 21A′ states reported in the previous sister Paper I, detailed quantum dynamics calculations are performed for these three adiabatic surfaces separately for J = 0 (J: total angular momentum quantum number). Overall reaction probabilities for O + HCl → OH + Cl and H + ClO, the branching ratio between the two reactions, effects of the initial rovibrational excitation, and product rovibrational distributions are evaluated in the total energy region E tot ≤ 0.9 eV. Significant contributions to the overall reaction dynamics are found from the two excited 11A′′ and 21A′ potential energy surfaces, clearly indicating the insufficiency of the dynamics only on the ground 11A′ surface. The detailed dynamics on the excited surfaces are reported in the third paper of this series.

INITIAL ROTATIONAL QUANTUM STATE EXCITATION AND ISOTOPIC EFFECTS FOR THE O(1D)+HCl → OH+Cl (OCl+H) REACTION

We present reaction probabilities, branching ratios and vibrational product quantum state distributions for the reaction O (1D)+ HCl → OH+Cl (OCl+H) , Boltzmann averaged over initial rotational quantum states at a temperature of 300 K and also for the deuterium isotopic variant. The quantum scattering dynamics are performed using the potential energy surfaces for all three contributing electronic states. Comparisons are presented with results computed using only the ground electronic state potential energy surface, with results computed using only the j = 0 initial rotational state and also with results obtained using an equal weighting for the lowest 10 rotational states. Inclusion of the higher initial rotational states significantly changes the form of the reaction probability as a function of collision energy, reducing the threshold for reaction on the 1A" and 2A' excited electronic states. We found that the combined inclusion of higher initial rotational states and all three contributing electronic states is crucial for obtaining a branching ratio that is within the range and trend given by experiment from our J = 0 calculations. Isotopic effects range from tunnelling effects for the hydrogen variant and enhancement of reactivity for the production of OD on the excited electronic states.

The dynamics of the O(1D) + HCl --> OH + Cl reaction at a 0.26 eV collision energy: a comparison between theory and experiment

The dynamics of the O((1)D) + HCl(v = 0, j = 0) --> Cl + OH reaction at a 0.26 eV collision energy has been investigated by means of a quasiclassical trajectory (QCT) and statistical quantum and quasiclassical methods. State-resolved cross sections and Cl atom velocity distributions have been calculated on two different potential energy surfaces (PESs): the H2 surface (Martinez et al. Phys. Chem. Chem. Phys. 2000, 2, 589) and the latest surface by Peterson, Bowman, and co-workers (PSB2) (J. Chem. Phys. 2000, 113, 6186). The comparison with recent experimental results reveals that the PSB2 PES manages to describe correctly differential cross sections and the velocity distributions of the departing Cl atom. The calculations on the H2 PES seem to overestimate the OH scattering in the forward direction and the fraction of Cl at high recoil velocities. Although the comparison of the corresponding angular distributions is not bad, significant deviations with a statistical description are found, thus ruling out a complex-forming mechanism as the dominant reaction pathway. However, for the ClO + H product channel, the QCT and statistical predictions are found to be in good agreement.

Quantum mechanics and quasiclassical study of the H/D+FO --> OH/OD+F, HF/DF+O reactions: chemical stereodynamics

The time-dependent quantum wave packet and the quasi-classical trajectory (QCT) calculations for the title reactions are carried out using three recent-developed accurate potential energy surfaces of the 1(1)A', 1(3)A', and 1(3)A'' states. The two commonly used polarization-dependent differential cross sections, dsigma(00)/domega(t), dsigma(20)/domega(t), with omega(t) being the polar coordinates of the product velocity omega', and the three angular distributions, P(theta(r)), P(Phi(r)), and P(theta(r),Phi(r)), with theta(r), Phi(r) being the polar angles of the product angular momentum, are generated in the center-of-mass frame using the QCT method to gain insight into the alignment and the orientation of the product molecules. Influences of the potential energy surface, the collision energy, and the isotope mass on the stereodynamics are shown and discussed. Validity of the QCT calculation has been examined and proved in the comparison with the quantum wave packet calculation.