Quasi-classical Trajectory Reaction Probabilities Research Articles

Quantum and classical dynamics of H + CaCl(X (2)Σ(+)) → HCl + Ca((1)S) reaction and vibrational energy levels of the HCaCl complex.

We carried out accurate quantum wave packet as well as quasi-classical trajectory (QCT) calculations for H + CaCl (νi = 0, ji = 0) reaction occurring on an adiabatic ground state using the recent ab initio potential energy surface to obtain the quantum and QCT reaction probabilities for several partial waves (J = 0, 10, and 20) as well as state resolved QCT integral and differential cross sections. The complete list of vibrational energy levels supported by the intermediate HCaCl complex is also obtained using the Lanczos algorithm. The QCT reaction probabilities show excellent agreement with the quantum ones except for the failure in reproducing the highly oscillatory resonance structure. Despite the fact that the reaction is exothermic and the existence of a barrier that is energetically lower than the bottom of the reactant valley, the reaction probability for J = 0 shows threshold-like behavior and the reactivity all through the energies is very low (<0.1). The dynamical features at two different energy regions (<0.35 eV and >0.35 eV) are found to be different drastically from each other. The analyses of these results suggest that the reaction is governed by one of the two different types of reaction mechanism, one is the direct mechanism at the high energy region and the other is the indirect mechanism at the low energy region by which the reaction proceeds through the long-lived intermediate complex followed by a statistical dissociation into asymptotic channels.

Accurate Time-Dependent Wave Packet Calculations for the O(+) + H2 → OH(+) + H Ion-Molecule Reaction.

Accurate quantum reactive scattering time-dependent wave packet close-coupling calculations have been carried out to determine total reaction probabilities and integral cross sections for the O(+) + H2 → OH(+) + H reaction in a range of collision energies from 10(-3) eV up to 1.0 eV for the H2 rovibrational states (v = 0; j = 0, 1, 2) and (v = 1; j = 0) using the potential energy surface (PES) by Martı́nez et al. As expected for a barrierless reaction, the reaction cross section decays rapidly with collision energy, Ec, following a behavior that nearly corresponds to that predicted by the Langevin model. Rotational excitation of H2 into j = 1, 2 has a very moderate effect on reactivity, similarly to what happens with vibrational excitation below Ec ≈ 0.3 eV. However, at higher collision energies the cross section increases notably when H2 is promoted to v = 1. This effect is explained by resorting to the effective potentials in the entrance channel. The integral cross sections have been used to calculate rate constants in the temperature range 200-1000 K. A good overall agreement has been found with the available experimental data on integral cross sections and rate constants. In addition, time-independent quantum mechanical and quasi-classical trajectory (QCT) calculations have been performed on the same PES aimed to compare the various methodologies and to discern the detailed mechanism of the title reaction. In particular, the analysis of individual trajectories has made it possible to explain, in terms of the coupling between reagent relative velocity and the topography of the PES, the presence of a series of alternating maxima and minima in the collision energy dependence of the QCT reaction probabilities for the reactions with H2(v=0,1,j=0), which are absent in the quantum mechanical calculations.

The effect of collision energy on the stereodynamics of the reaction H(2S) + NH (X3 Σ−, v = 0, j = 0) → N(4S) + H2

The quasi-classical trajectory (QCT) is calculated to study the stereodynamics properties of the title reaction H(2S) + NH(X3 Σ−) → N(4S) + H2 on the ground state 4A″ potential energy surface (PES) constructed by Zhai and Han [2011 J. Chem. Phys. 135 104314]. The calculated QCT reaction probabilities and cross sections are in good agreement with the previous theoretical results. The effects of the collision energy on the k—k′ distribution and the product polarization of H2 are studied in detail. It is found that the scattering direction of the product is strongly dependent on the collision energy. With the increase in the collision energy, the scattering directions of the products change from backward scattering to forward scattering. The distribution of P(θr) is strongly dependent on the collision energy below the lower collision energy (about 11.53 kcal/mol). In addition, the P(φr) distribution dramatically changes as the collision energy increases. The calculated QCT results indicate that the collision energy plays an important role in determining the stereodynamics of the title reaction.

Time-Dependent Wave Packet Quantum and Quasi-Classical Trajectory Study of He + H2+, D2+→ HeH++ H, HeD++ D Reaction on an Accurate FCI Potential Energy Surface

The quantum scattering dynamics and quasi-classical trajectory (QCT) calculations have been carried out for the title reaction on an accurate potential energy surface (PES) computed using the full configuration interaction (FCI). On the basis of the PES, the integral cross-sections of He + H₂⁺ (v = 0-3, j = 1) → HeH⁺ + H reaction have been calculated, and the results are generally agreed with the experimental cross-sections obtained by Tang et al. [J. Chem. Phys. 2005, 122, 164301] after taking into account the experimental uncertainties, which proves the reliability of implementing dynamics calculations on the FCI PES. The reaction probability of He + D₂⁺ (v = 0-2, j = 0) → HeD⁺ + D reactions for total angular momentum J = 0 and the integral cross-section (ICS) have been calculated. The significant quantum effect has been explored by the comparison between the QCT reaction probabilities (or ICS) and the quantum mechanical (QM) reaction probabilities (or ICS), which may be attributed to the deep well in the PES of this light atoms system. Furthermore, the role of Coriolis coupling (CC) effects has also been found not important by the comparison between the CC calculation and the centrifugal sudden (CS) approximation calculation, except that the CC total cross-sections for the v = 1 and 2 states show the collision energy-dependent behaviors in the low-energy area, which are different from those based on the CS calculation.

Quasi-classical trajectory study of the dynamics of the reaction F + DCl ( v = 0, j = 0) → DF + Cl

Theoretical studies of the dynamics of the reaction F + DCl( v = 0, j = 0) → DF + Cl are performed with quasi-classical trajectory (QCT) method on a recently computed 1 2 A′ ground-state surface reported by Deskevich et al. [33]. The calculated QCT reaction probabilities for total angular momentum J = 0 are in good agreement with earlier quantum wave packet results calculated by Sun et al. [35] over the collision energy range from 4 to 30 kcal/mol. The integral cross-sections as functions of collision energy are presented. The differential cross-sections are governed by the direct reaction dynamics that follow the minimum energy path at both low and high collision energies. The rotational angular momentum vectors j′ of the product DF are not only aligned, but also oriented along the y-axis. The degrees of alignment and orientation of DF in reaction F + DCl( v = 0, j = 0) → DF + Cl differ from that of HF in reaction F + HCl( v = 0, j = 0) → HF + Cl. The differences in vector properties of DF in reaction F + DCl between that of HF in reaction F + HCl may be attributed to the difference in the mass factor in the two reactions.

Time-dependent wave packet and quasiclassical trajectory study of the C(P3)+OH(X Π2)→CO(X Σ1+)+H(S2) reaction at the state-to-state level

The first calculations of state-to-state reaction probabilities and product state-resolved integral cross sections at selected collision energies (0.05, 0.1, 0.5, and 1.0 eV) for the title reaction on the ab initio potential energy surface of [Zanchet et al. J. Phys. Chem. A 110, 12017 (2006)] with the OH reagent in selected rovibrational states (v = 0-2, j = 0-5) have been carried out by means of the real wave packet (RWP) and quasiclassical trajectory (QCT) methods. State-selected total reaction probabilities have been calculated for total angular momentum J = 0 in a broad range of collision energies. Integral cross sections and state-specific rate coefficients have been obtained from the corresponding J = 0 RWP reaction probabilities for initially selected rovibrational states by means of a capture model. The calculated RWP and QCT state-selected rate coefficients are practically temperature independent. Both RWP and QCT reaction probabilities, integral cross sections, and rate coefficients are almost independent of the initial rotational excitation. The RWP results are found to be in an overall good agreement with the corresponding QCT results. The present results have been compared with earlier wave packet calculations carried out on the same potential energy surface.

Quantum mechanical and quasi-classical trajectory reaction probabilities and cross sections for the S(1D) + H2,D2,HD insertion reactions

Time-independent quantum mechanical (QM) and quasi-classical trajectory (QCT) calculations of reaction probabilities at total angular momentum J = 0 as a function of collision energy for the S(1D) + H2(v = 0, j = 0), S(1D) + D2(v = 0, j = 0) and S(1D) + HD(v = 0, j = 0) reactions have been performed on a recent ab initio potential energy surface. In addition, QCT calculations of integral cross sections as a function of collision energy (the excitation functions) have been carried out for the same reactions. The QCT excitation functions and those obtained by applying a capture model to the QM reaction probabilities are compared with the available experimental determinations. The QCT and QM methods reproduce the shape of the measured excitation functions quite satisfactorily. However, the theoretical intramolecular and intermolecular isotope effects are in disagreement with those obtained experimentally.

Theoretical Reaction Dynamics Study of the Effect of Vibrational Excitation of CO on the OH + CO → H + CO2 Reaction

The OH + CO → H + CO2 reaction has received a great deal of attention in recent years, being presently the prototypical complex-forming four-atom reaction. An interesting issue is the extent to which the vibration of the nonreactive CO bond acts as a spectator in the reaction. To get insight into this question, we report a study of the reactivity of the ground (ν = 0, j = 0) and first excited vibrational state (ν = 1, j = 0) of CO with the OH diatom in its ground rovibrational state (ν = 0, j = 0). For these reactions, the time-dependent wave packet (TDWP) method was used to calculate exact, full-dimensional (6D) initial-state selected reaction probabilities on the Bradley-Schatz potential energy surface (PES), for total angular momentum J = 0. An approximate diabatic (potential-averaged five-dimensional, PA5D) model was also used, in which the 6D potential is averaged over one asymptotic CO vibrational wave function. The results show a large increase in reactivity upon vibrational excitation of CO, particularly in the 6D model. A comparison of the 6D results with the diabatic PA5D results for CO (ν = 1), as well as the analysis of the potential curves constructed according to an adiabatic 5 + 1D model, reveal that this effect is mostly due to vibrationally inelastic energy transfer from the CO bond to the reaction coordinate. The reactivity of CO (v = 1) is much higher in the 6D than in the PA5D model. These findings allow us to conclude that the CO bond does not act as a spectator in the reaction. Finally, the quasiclassical trajectory (QCT) method was employed on the above-mentioned Bradley-Schatz PES, as well as on the most recent PES (LTSH). The QCT method is able to predict quite well the difference between the 6D and PA5D reaction probabilities for CO (ν = 1) obtained with the TDWP method on the BS PES. The PA5D QCT results are also in good agreement with 6D and PA5D TDWP results for reaction of CO (ν = 0) and for the BS PES. The large differences found between QCT reaction probabilities for CO (ν = 1) in the 6D and the PA5D model, on one hand, and the large differences between 6D QCT results for CO (ν = 1) and PA5D QCT results for CO (ν = 0), on the other hand, for the LTSH PES, strongly suggest that our conclusion (CO does not act as a spectator) can be generalized to this newer PES.

Dynamics of the S(1D) + H2 Insertion Reaction: A Combined Quantum Mechanical and Quasiclassical Trajectory Study

Accurate three-dimensional quantum mechanical (QM) scattering calculations of integral and differential cross sections for the S(1D) + H2 (v = 0, j = 0, 1) insertion reaction have been carried out at a collision energy of 2.24 kcal/mol. Additionally, quasiclassical trajectory (QCT) calculations have been performed for the same reaction at 2.24 and 3.96 kcal/mol collision energies. The assignment of product quantum states in the QCT method has been carried out using a Gaussian-weighted binning procedure, which has proved to be more accurate than the usual histogramatic method. QM and QCT reaction probabilities at total angular momentum J = 0 as a function of collision energy within the range 0−11.5 kcal/mol for the S(1D) + H2 (v = 0, j = 0) reaction are also reported. The theoretical results have been used to simulate the available experimental data in the form of differential cross sections and product translational energy distributions. A general good agreement is found between theory and experiment for this prototypic insertion reaction.