Real wave packet and flux analysis studies of the H + F2 → HF + F reaction

The H + F₂ → HF + F reaction on ground state potential energy surface is investigated using the quantum mechanical real wave packet and Flux analysis method based on centrifugal sudden approximation. The initial state selected reaction probabilities for total angular momentum J = 0 have been calculated by both methods while the probabilities for J > 0 have been calculated by Flux analysis method. The initial state selected reaction probabilities, integral cross sections and rate coefficients have been calculated for a broad range of collision energy. The results show a large rotational enhancement of the reaction probability. Some resonances were seen in the state‐to‐state reaction probabilities while state‐to‐all reaction probabilities and the reaction cross section do not manifest any oscillations and the initial state selected reaction rate constants are sensitive to the temperature. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Quantum wave packet calculation of reaction probabilities,cross sections,and rate constants for H+ + LiH → Li + H reaction

The H⁺ + LiH → Li + H reactive scattering has been studied using a quantum real wave packet method. The state‐to‐state and state‐to‐all reaction probabilities for the entitled collision have been calculated at zero total angular momentum. The probabilities for J > 0 are estimated from the J = 0 results by using J‐shifting approximation based on the Capture model. The integral cross sections and thermal rate constants are then calculated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

On the dynamics of the H+ +D2(v=0,j=0)-->HD+D + reaction: a comparison between theory and experiment

The H+ +D2(v=0,j=0)-->HD+D + reaction has been theoretically investigated by means of a time independent exact quantum mechanical approach, a quantum wave packet calculation within an adiabatic centrifugal sudden approximation, a statistical quantum model, and a quasiclassical trajectory calculation. Besides reaction probabilities as a function of collision energy at different values of the total angular momentum, J, special emphasis has been made at two specific collision energies, 0.1 and 0.524 eV. The occurrence of distinctive dynamical behavior at these two energies is analyzed in some detail. An extensive comparison with previous experimental measurements on the Rydberg H atom with D2 molecules has been carried out at the higher collision energy. In particular, the present theoretical results have been employed to perform simulations of the experimental kinetic energy spectra.     

Exact quantum calculations on the collinear hydrogen atom transfer reaction I. Study on oscillations of the reaction probabilities of Cl + HCl

1-D quantum calculations of reaction probabilities have been carried out for the collinear reaction Cl + HCl (v≤3)→ClH (v′≤3) + Cl using hyperspherical coordinates. An LEPS potential energy surface with a shallow well depth of ?3.22 KJ/mol has been used in the calculations. The state-to-state reaction probabilities have been calculated. According to the results obtained we found that the diagonal (v=v′) reaction probabilities dominate over the off-diagonal (v≠v′) reaction probabilities and the largest off-diagonal reaction probabilities are smaller than 0.1. The reaction probabilities show oscillation as a function of energy. Dynamic resonances strengthen for the potential energy surface with a well.     

Quantum wave packet study of the insertion reaction S+H2

S(¹D)+H₂→SH+H reaction at zero total angular momentum has been studied by using a time-dependent quantum real wave packet method. State-to-state and state-to-all reactive scattering probabilities for a broad range of energy are calculated. The probabilities show many sharp peaks that ascribed to reactive scattering resonances. The density plots of the wave function shows that the reaction presents a pure insertion pathway.     

A quantum wave packet dynamics study of the N(2D) + H2 reaction

We report a dynamics study of the reaction N((2)D) + H(2) (v=0, j=0-5) --> NH + H using the time-dependent quantum wave packet method and a recently reported single-sheeted double many-body expansion potential energy surface for NH(2)(1(2)A' ') which has been modeled from accurate ab initio multireference configuration-interaction calculations. The calculated probabilities for (v=0, j=0-5) are shown to display resonance structures, a feature also visible to some extent in the calculated total cross sections for (v=0, j=0). A comparison between the calculated centrifugal-sudden and coupled-channel reaction probabilities validate the former approximation for the title system. Rate constants calculated using a uniform J-shifting scheme and averaged over a Boltzmann distribution of rotational states are shown to be in good agreement with the available experimental values. Comparisons with other theoretical results are also made.     

Real wave packet and quasiclassical trajectory studies of the H+ + LiH reaction

Time-dependent real wave packet (RWP) and quasiclassical trajectory (QCT) calculations have been carried out to study the H(+) + LiH reaction on the ab initio potential-energy surface of Martinazzo et al. [J. Chem. Phys., 2003, 119, 11241]. Total initial state-selected and final state-resolved reaction probabilities for the two possible reaction channels, H(2)(+) + Li and LiH + H(+), have been calculated for total angular momentum J=0 at a broad range of collision energies. Integral cross sections and thermal rate coefficients have been calculated using the QCT method and from the corresponding J=0 RWP reaction probabilities by means of a capture model. The calculated thermal rate coefficients are found to be nearly independent of temperature in the 100-500 K interval with a value of approximately 10(-9) cm(3) s(-1), which is in good agreement with estimates used in evolutionary models of early-Universe lithium chemistry. The RWP results are found to be in good agreement overall with the corresponding QCT calculations.     

A quantum reaction dynamics study of the translational, vibrational, and rotational motion effects on the HD + H3+ reaction

Time-dependent, quantum reaction dynamics wavepacket approach is employed to investigate the impacts of the translational, vibrational, and rotational motion on the HD+H(3)(+) → H(2)D(+) + H(2) reaction using the Xie-Braams-Bowman potential energy surface [Z. Xie, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 122, 224307 (2005)]. We treat this five atom reaction with a seven-degree-of-freedom model by fixing one Jacobi and one torsion angle related to H(3) (+) at the lowest saddle point geometry of the potential energy surface. The initial state selected reaction probabilities show that the rotational excitations of H(+)-H(2) greatly enhance the reactivity with the reaction probabilities increased double at high rotational states compared to the ground state. However, the vibrational excitations of H(3) (+) hinder the reactivity. The ground state reaction probability shows no reaction threshold for this exoergic reaction, and as the translational energy increases, the reaction probability decreases. Furthermore, reactive resonances and zero point energy play very important roles on the reaction dynamics. The obtained integral cross section has the character of an exoergic reaction without a threshold: it decreases with the translational energy increasing. The calculated thermal rate constants using this seven-degree-of-freedom model are in agreement with a later experiment measurement.     

Quantum dynamics study on the product branching for the C(3P) + C2H2 reaction: cyclic-C3H versus linear-C3H

Reduced-dimensionality quantum reactive scattering calculations for the C(3P) + C2H2 reaction have been carried out in order to understand the product branching dynamics of cyclic-C3H + H and linear-C3H + H. Our model treats only two degrees of freedom but can explicitly describe both of the C3H isomer product channels. The lowest triplet potential energy surface has been obtained by the hybrid density-functional method at the B3LYP/6-31G(d,p) level of theory. The calculated reaction probabilities were found to be dominated by resonance consistent with the complex-formation potential, and the results show that cyclic-C3H is preferentially formed via the cyclic-C3H2 intermediate produced by insertion of C(3P) into the CC bond. We have found that the isomerization from the cyclic-C3H2 to linear-C3H2 intermediate is suppressed by a barrier separating potential wells corresponding to these two intermediates. It has also been found that the energy dependence of the calculated total reaction cross section is in good agreement with the result of crossed molecular beam experiments.     

Exact quantum and TST-CEQ study of the collinear reaction O+HCl

Exact quantum calculations of reaction probabilities have been carried out using hyperspherical coordinates for the collinearr reaction O+HCl(v <1) -OH(v'<1)+Cl . A generalized LEPS potential energy surface with a barrier height of 8.12 kcal/mol has been used in the calculations. According to the calculated results we found that (1) the reaction probability oscillates with energy, (2) the reaction probability shows vibrational adiabaticity, although it is poorer than that for symmetric reaction Cl + HC1. The analysis of resonance has also been done. The reaction rate constants and average cross sections have been calculated by TST-CEQ method. The rate constants are in agreement with that by QCT and smaller than the experimental one. Finally, the threshold has been estimated and is in good agreement with that of the literature.     

Time dependent quantum dynamics study of the Ne + H2+(v=0-4)-->NeH+ + H proton transfer reaction

The Ne + H2+-->NeH+ + H proton transfer reaction was studied using the time dependent real wave packet quantum dynamics method at the helicity decoupling level, considering the H2+ molecular ion in the (v=0-4, j=0) vibrorotational states and a wide collision energy interval. The calculated reaction probabilities and reaction cross sections were in a rather good agreement with reanalyzed previous exact quantum dynamics results, where a much smaller collision energy interval was considered. Also, a quite good agreement with experimental data was found. These results suggested the adequacy of the approach used here to describe this and related systems.     

Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: the dynamics on two different potential energy surfaces

The possible existence of a complex-forming pathway for the H+O(2) reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6 eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O(2)(v=0,j=1)-->OH(v(')=1,j('))+O process reasonably well.     

Quantum dynamics study of H+NH3-->H2+NH2 reaction

We report in this paper a quantum dynamics study for the reaction H+NH3-->NH2+H2 on the potential energy surface of Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The quantum dynamics calculation employs the semirigid vibrating rotor target model [J. Z. H. Zhang, J. Chem. Phys. 111, 3929 (1999)] and time-dependent wave packet method to propagate the wave function. Initial state-specific reaction probabilities are obtained, and an energy correction scheme is employed to account for zero point energy changes for the neglected degrees of freedom in the dynamics treatment. Tunneling effect is observed in the energy dependency of reaction probability, similar to those found in H+CH4 reaction. The influence of rovibrational excitation on reaction probability and stereodynamical effect are investigated. Reaction rate constants from the initial ground state are calculated and are compared to those from the transition state theory and experimental measurement.     

Constraints at the transition state of the D + H2 reaction: quantum bottlenecks vs. stereodynamics

This article presents a quasiclassical trajectory method for the calculation of cumulative reaction probabilities by sampling of the helicity quantum number of the reagents (k). The method is applied to the D + H(2) reaction at various total angular momentum (J) values, and the helicity-resolved quasiclassical cumulative reaction probabilities are compared to their quantum mechanical counterparts. The agreement between the two sets of results is fairly good. In particular, k-dependent, J-independent reaction thresholds found with quantum methods are reproduced by the quasiclassical calculations. The shift of these thresholds with increasing k, which has been previously attributed to the quantum bottleneck states taking part in the reaction, is revisited and discussed also in terms of the reaction stereodynamics.     

Calculations on the rate of the ion-molecule reaction between NH3+ and H2

The rate coefficient for the ion-molecule reaction NH3(+) + H2 --> NH4(+) + H has been calculated as a function of temperature with the use of the statistical phase space approach. The potential surface and reaction complex and transition state parameters used in the calculation have been taken from ab initio quantum chemical calculations. The calculated rate coefficient has been found to mimic the unusual temperature dependence measured in the laboratory, in which the rate coefficient decreases with decreasing temperature until 50-100 K and then increases at still lower temperatures. Quantitative agreement between experimental and theoretical rate coefficients is satisfactory given the uncertainties in the ab initio results and in the dynamics calculations. The rate coefficient for the unusual three-body process NH3(+) + H2 + He --> NH4(+) + H + He has also been calculated as a function of temperature and the result found to agree well with a previous laboratory determination.     

Time-dependent quantum study of the kinetics of the H(2S) + FO(2II) OH(2II) + F(2P) reaction

Quantum mechanical wave packet calculations are carried out for the H((2)S) + FO((2)II) --> OH((2)II) + F((2)P) reaction on the adiabatic potential energy surface of the ground (3)A' triplet state. The state-to-state and state-to-all reaction probabilities for total angular momentum J = 0 have been calculated. The probabilities for J > 0 have been estimated from the J = 0 results by using J-shifting approximation based on a capture model. Then, the integral cross sections and initial state-selected rate constants have been calculated. The calculations show that the initial state-selected reaction probabilities are dominated by many sharp peaks. The reaction cross section does not manifest any sharp oscillations and the initial state-selected rate constants are sensitive to the temperature.     

A full dimensional, nine-degree-of-freedom, time-dependent quantum dynamics study for the H2+C2H reaction

A full dimensional, nine-degree-of-freedom (9DOF), time-dependent quantum dynamics wave packet approach is presented for the study of the H2+C2H-->H+C2H2 reaction system. This is the first full dimensional quantum dynamics study for a diatom-triatom reaction system. The effects of the initial vibrational and rotational excitations of the reactants on the reactivity of this reaction are investigated. This study shows that vibrational excitations of H2 enhance the reactivity; whereas, the vibrational excitations of C2H only have a small effect on the reaction probability. In addition, the bending excitations of C2H, compared to the ground state reaction probability, hinder the reactivity. Comparison of the ground state reaction probabilities of the 9DOF and 8DOF shows the reaction probability from the full dimensional calculation is larger, with more prominent resonance features.     

三维含时量子散射研究H+ClH体系

用三维含时量子散射理论模拟了H+GlH体系在BW2,mBW2,G3势能面上的动力学行为.其计算结果表明,振动量子态对反应几率影响很大;势能面的地形对转动量子态如何影响反应几率起重要作用;反应几率表现出"黄金规则".此外,BW2,mBW2势能面上的反应几率几乎相同,而G3势能面上的反应几率较前者低,大概由于G3的势垒高的缘故.     

三维含时量子散射研究H + CIH体系

用三维含时量子散射理论模拟了H+CIH体系在BW2,mBW2,G3势能面上的动力学行为,其计算结果表明,振动量子态对反应几率影响很大;势能面的地形对转动量子态如何影响反应几率起重要作用;反应几率表现出“黄金规则”,此外,BW2,mBW2势能面上的反应几率几乎相同,而G3势能面上的反应几率较前者低,大概由于G3的势垒高的缘故。