The effect of collision energy on the stereodynamics of the reaction H(~2S)+NH(X~3∑~-,v = 0,j = 0)→ N(~4S)+H_2

The quasi-classical trajectory(QCT) is calculated to study the stereodynamics properties of the title reaction H(2S)+NH(X3∑-) →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.     

Vector correlations study of the reaction N(~2D) + H_2(X~1Σ_g~+) →NH(a~1?) + H(~2S) with different collision energies and reagent vibration excitations

Vector correlations of the reaction N(2D)+ H2(X1Σ+g) → NH(a1?)+ H(2S) are studied based on a recent DMBESEC PES for the first excited state of NH2[J. Phys. Chem. A 114 9644(2010)] by using a quasi-classical trajectory method.The effects of collision energy and the reagent initial vibrational excitation on cross section and product polarization are investigated for v = 0–5 and j = 0 states in a wide collision energy range(10–50 kcal/mol). The integral cross section could be increased by H2 vibration excitation remarkably based on the DMBE-SEC PES. The different phenomena of differential cross sections with different collision energies and reagent vibration excitations are explained. Particularly,the NH molecules are scattered mainly in the backward hemisphere at low vibration quantum number and evolve from backward to forward direction with increasing vibration quantum number, which could be explained by the fact that the vibrational excitation enlarges the H–H distance in the entrance channel, thus enhancing the probability of collision between N atom and H atom. A further study on product polarization demonstrates that the collision energy and vibrational excitation of the reagent remarkably influence the distributions of P(θr), P(φr), and P(θr, φr).     

Mechanism analysis of reaction S~+(~2D)+H_2(X~1Σ_g~+) → SH~+(X~3Σ~-) + H(~2S) based on the quantum state-to-state dynamics

We present a state-to-state dynamical calculation on the reaction S~++ H_2→ SH~+ +H based on an accurate ~X2 A~″ potential surface. Some reaction properties, such as reaction probability, integral cross sections, product distribution, etc.,are found to be those with characteristics of an indirect reaction. The oscillating structures appearing in reaction probability versus collision energy are considered to be the consequence of the deep potential well in the reaction. The comparison of the present total integral cross sections with the previous quasi-classical trajectory results shows that the quantum effect is more important at low collision energies. In addition, the quantum number inversion in the rotational distribution of the product is regarded as the result of the heavy–light–light mass combination, which is not effective for the vibrational excitation. For the collision energies considered, the product differential cross sections of the title reaction are mainly concentrated in the forward and backward regions, which suggests that there is a long-life intermediate complex in the reaction process.     

The effect of the rotational excitation of NO on the stereodynamics for the reaction C(~3P)+NO(X~2Π)→CN(X~2Σ~+)+O(~3P)

The stereodynamic properties of the reaction C(3P)+NO(X2Π)→CN(X2Σ+)+O(3P) in different rotational states of reactant NO are studied theoretically by using the quasiclassical trajectory method on 2A' and 2A' potential energy surfaces(PESs) at a collision energy of 0.06 eV.The vector properties in different rotational states on the two surfaces are discussed in detail.The results indicate that the rotational excitation of NO has considerable influence on the stereodynamic property of the reaction occurring on the two surfaces.At the same time,the calculated polarization-dependent differential cross sections(PDDCSs) in different initial rotational states manifest that products are strongly polarized at three scattering angles.     

State-to-state dynamics of F(~2P) + HO(~2Π) → O(~3P) + HF(~1Σ~+)reaction on 1~3A〞 potential energy surface

State-to-state time-dependent quantum dynamics calculations are carried out to study F(~2P) + HO(~2Π) → O(~3P) +HF(~1Σ~+) reaction on 1~3A〞 ground potential energy surface(PES). The vibrationally resolved reaction probabilities and the total integral cross section agree well with the previous results. Due to the heavy–light–heavy(HLH) system and the large exoergicity, the obvious vibrational inversion is found in a state-resolved integral cross section. The total differential cross section is found to be forward–backward scattering biased with strong oscillations at energy lower than a threshold of 0.10 eV, which is the indication of the indirect complex-forming mechanism. When the collision energy increases to greater than 0.10 eV, the angular distribution of the product becomes a strong forward scattering, and almost all the products are distributed at θ_t = 0°. This forward-peaked distribution can be attributed to the larger J partial waves and the property of the F atom itself, which make this reaction a direct abstraction process. The state-resolved differential cross sections are basically forward-backward symmetric for v' = 0, 1, and 2 at a collision energy of 0.07 eV; for a collision energy of 0.30 eV,it changes from backward/sideward scattering to forward peaked as v increasing from 0 to 3. These results indicate that the contribution of differential cross sections with more highly vibrational excited states to the total differential cross sections is principal, which further verifies the vibrational inversion in the products.     

Energy and rotation-dependent stereodynamics of H(~2S) + NH(a~1?) → H_2(X~1Σ_g~+) + N(~2D) reaction

Quasi-classical trajectory calculations are performed to study the stereodynamics of the H(~2S) + NH(a~1?) →H_2(X~1Σ_g~+) + N(~2D) reaction based on the first excited state NH_2(1~2A') potential energy surface reported by Li et al.[Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644] for the first time. We observe the changes of differential cross-sections at different collision energies and different initial reagent rotational excitations. The influence of collision energy on the k–k' distribution can be attributed to a purely impulsive effect. Initial reagent rotational excitation transforms the reaction mechanism from insertion to abstraction. The effect of initial reagent rotational excitations on k–k' distribution can be explained by the rotational excitation enlarging the rotational rate of reagent NH in the entrance channel to reduce the probability of collision between incidence H atom and H atom of target molecular. We also investigate the changes of vector correlations and find that the rotational angular momentum vector j' of the product H_2 is not only aligned, but also oriented along the y axis. The alignment parameter, the disposal of total angular momentum and the reaction mechanism are all analyzed carefully to explain the polarization behavior of the product rotational angular moment.     

Effects of collision energy and rotational quantum number on stereodynamics of the reactions:H(~2S)+NH(v=0,j=0,2,5,10)→N(~4S)+H_2

The stereodynamical properties of H(~2S) + NH(v = 0,j = 0,2,5,10)→N(~4S) + H_2 reactions are studied in this paper by using the quasi-classical trajectory(QCT) method with different collision energies on the double many-body expansion(DMBE) potential energy surface(PES)(Poveda L A and Varandas A J C 2005 Phys.Chem.Chem.Phys.7 2867).In a range of collision energy from 2 to 20 kcal/mol,the vibrational rotational quantum numbers of the NH molecules are specifically investigated on v = 0 and j = 0,2,5,10 respectively.The distributions of P(θ_r),P(φ_r),P(θ_r,φ_r),(2π/σ)(dσ_(00)/dω_t)differential cross-section(DCSs) and integral cross-sections(ICSs) are calculated.The ICSs,computed for collision energies from 2 kcal/mol to 20 kcal/mol,for the ground state are in good agreement with the cited data.The results show that the reagent rotational quantum number and initial collision energy both have a significant effect on the distributions of the k-j',the k-k'-j',and the k-k' correlations.In addition,the DCS is found to be susceptible to collision energy,but it is not significantly affected by the rotational excitation of reagent.     

A typical slow reaction H（2S） ＋ S2（X3∑g） → SH（X2П） ＋S（3P） ona new surface： Quantum dynamics calculations

Quantum dynamics calculations for the title reaction H(2S) + S2(X3-Σg) → SH(X2Π) + S(3P) are performed by using a globally accurate double many-body expansion potential energy surface [J. Phys. Chem. A 115 5274(2011)].The Chebyshev real wave packet propagation method is employed to obtain the dynamical information, such as reaction probability, initial state-specified integral cross section, and thermal rate constant. It is found not only that there is a reaction threshold near 0.7 eV in both reaction probabilities and integral cross section curves, but also that both the probability and cross section increase firstly and then decrease as the collision energy increases. The existence of the resonance structure in both the probability and cross section curves is ascribed to the deep potential well. The calculation of the rate constant reveals that the reaction occurring on the potential energy surface of the ground-state HS2is slow to take place.     

Theoretical prediction of the optimal conditions for observing the stereodynamical vector properties of the C(~3P) + OH(X~2Π) → CO(X~1 Σ~+) + H(~2S) reaction

The best optimal initial reactant state and collision energy for observing the stereodynamical vector properties of the title reaction in the ground electronic state X2A potential energy surface(PES) [Zanchet et al. 2006 J. Phys. Chem. A 110 12017] are theoretically predicted using the quasi-classical trajectory(QCT) method for the first time. The calculated results reveal that the smallest value of the rotational quantum number j, larger vibrational quantum number v, and the lower strength of collision energy should be selected for offering the most obvious picture about the stereodynamical vector properties. Polarization-dependent differential cross sections and the angular momentum alignment distribution, P(θr) and P(Φr) in the center-of-mass frame, are obtained to gain an insight into the alignment and orientation of the product molecules. The rotational angular momentum vector j of CO is aligned to be perpendicular to reagent relative velocity k. The product polarizations align along the y axis, pointing to the positive direction of the y axis. A new method is developed to investigate massive reactions with various initial states and to further study the vector properties of the fundamental reactions in detail.     

Non-adiabatic quantum dynamical studies of Na(3p) + HD(v = 1, j5) = 0)→NaH/NaD + D/H reaction

Non-adiabatic dynamical calculations are carried out for the Na(3 p)+HD(ν = 1, j = 0)→NaH/NaD+D/H reaction on the diabatic potential energy surfaces of Wang et al.(Sci. Rep. 2018, 8, 17960) by using the time-dependent wave packet method. The state-to-state integral cross sections and differential cross sections of two reaction channels(NaH/NaD+D/H)are calculated for collision energy up to 0.4 eV. The cross section branching ratio indicates that the dominant reaction channel changes from NaD+H to NaH+D when the collision energy is larger than 0.227 eV. The products from two reaction channels both prefer to form in vibrationally cold but rotationally hot states, and they both tend to forward scattering.     

Quasiclassical trajectory theoretical study on the chemical stereodynamics of the O(~1D)+H_2→OH+H reaction and its isotopic variants (HD,D_2)

The quasiclassical trajectory (QCT) method is used to study stereodynamic information about the reaction O ( 1 D) + H 2 →OH + H on the DK (Dobbyn and Knowles) (1 1 A' ) ab initio potential energy surface (PES). A wide scale of collision energy (E c ) from 0.05 eV to 0.5 eV is considered in the dynamic calculations. To reveal the rovibrational excitation effect, calculations at a collision energy of 0.52 eV are carried out for the v = 0 ～ 5, j = 0 and v = 0, j = 0 ～ 15 initial states. The two popularly used polarization-dependent differential cross sections (PDDCSs), dσ 00 /dω t (0, 0) and dσ 20 /dω t (2, 0), and two angular distributions, P(θ r ) and P( r ) are calculated to obtain an insight into the alignment and the orientation of the product molecules. From the calculations, we can obtain that the alignment of the OH product is weaker at high collision energy and becomes stronger with the increase of initial vibrational level, and it is almost insensitive to the initially rotational excitation. Influences of the mass values of isotopes (HD, D 2 ) on the stereodynamics are also shown and discussed. Comparisons between available theoretical results and experimental results are made and discussed.     

Quasi-classical trajectory study of H+LiH(v=0,1,2,j=0)→Li+H_2 reaction on a new global potential energy surface

Quasi-classical trajectory(QCT) calculations are reported for the H+LiH(v = 0–2, j = 0)→Li+H_2 reaction on a new ground electronic state global potential energy surface(PES) of the LiH_2 system. Reaction probability and integral cross sections(ICSs) are calculated for collision energies in the range of 0 eV–0.5 eV. Reasonable agreement is found in the comparison between present results and previous available theoretical results. We carried out statistical analyses with all the trajectories and found two main distinct reaction mechanisms in the collision process, in which the stripping mechanism(i.e., without roaming process) is dominated over the collision energy range. The polarization dependent differential cross sections(PDDCSs) indicate that forward scattering dominates the reaction due to the dominated mechanism. Furthermore,the reactant vibration leads to a reduction of the reactivity because of the barrierless and attractive features of PES and mass combination of the system.     

Theoretical study of stereodynamics for the D'+ DS(v=0,j=0) → D'D + S abstraction reaction

Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D'+ DS(v = 0, j = 0) → D'D + S on a new LZHH potential energy surface (PES) of the adiabatic 3 A electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θr), P(φr), and P(θr,φr), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt), (2π/σ)(dσ21/dωt)) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.     

Reaction mechanism of D + ND→N + D_2 and its state-to-state quantum dynamics

The quantum state-to-state calculations of the D + ND→N + D_2 reaction are performed on a potential energy surface of 4 A' state. The state-resolved integral and differential cross sections and product state distributions are calculated and discussed. It is found that the rotational distribution, rather than the vibrational distribution, of the product has an obvious inversion. Due to the fact that it is a small-impact-parameter collision, its product D_2 is mainly dominated by rebound mechanism, which can lead to backward scattering at low collision energy. As the collision energy increases, the forward scattering and sideward scattering begin to appear. In addition, the backward collision is also found to happen at high collision energy, through which we can know that both the rebound mechanism and stripping mechanism exist at high collision energy.     

Stereo-dynamics of the exchange reaction HaWLiHb → LiHa＋Hb and its isotopic variants

<正>The quasi-classical trajectory(QCT) method is used to calculate the stereo-dynamics of the exchange reaction H_a+LiH_b→LiH_a+H_b and its isotopic variants based on an accurate potential energy surface reported by Prudente et al.[Prudente F V,Marques J M C and Maniero A M 2009 Chem.Phys.Lett.474 18].The reactive probability of the title reaction is computed.The vector correlations and four polarization-dependent generalized differential cross sections(PDDCSs) at different collision energies are presented.The influences of the collision energy and the reagent rotation on the product polarization are studied in the present work.The results indicate that the product rotational angular momentum j’ is not only aligned,but also oriented along the direction perpendicular to the scattering plane. The product polarization distributions of the title reaction and its isotopic variants exhibit distinct differences which may arise from different mass combinations.     

Theoretical prediction of energy dependence for D+BrO→DBr+O reaction:The rate constant and product rotational polarization

A quasi-classical trajectory(QCT) calculation is used to investigate the vector and scalar properties of the D + Br O → DBr + O reaction based on an ab initio potential energy surface(X1A state) with collision energy ranging from 0.1 kcal/mol to 6 kcal/mol. The reaction probability, the cross section, and the rate constant are studied. The probability and the cross section show decreasing behaviors as the collision energy increases. The distribution of the rate constant indicates that the reaction favorably occurs in a relatively low-temperature region(T 100 K). Meanwhile, three product angular distributions P(θr), P(φr), and P(θr, φr) are presented, which reflect the positive effect on the rotational angular momentum j' polarization of the DBr product molecule. In addition, two of the polarization-dependent generalized differential cross sections(PDDCSs), PDDCS00 and PDDCS20, are computed as well. Our results demonstrate that both vector and scalar properties have strong energy dependence.     

Effect of reagent vibrational excitation and isotope substitution on the stereo-dynamics of the Ba+HF→BaF+H reaction

Based on an extended London-Eyring-Polanyi-Sato (LEPS) potential energy surface (PES), the Ba + HF reaction has been studied by the quasi-classical trajectory (QCT) method. The reaction integral cross section as a function of collision energy for the Ba + HF → BaF + H reaction is presented and the influence of isotope substitution on the differential cross sections (DCSs) and alignments of the product's rotational angular momentum have also been studied. The results suggest that the integral cross sections increase with increasing collision energy, and the vibrational excitation of the reagent has great influence on the DCS. In addition, the product's rotational polarization is very strong as a result of heavy-heavy-light (HHL) mass combination, and the distinct effect of isotope substitution on the stereodynamics is also revealed.     

Stereodynamics in reaction O（1D） ＋ CH4 〉OH ＋ CH3

A theoretical study of the stereodynamics for reaction O(1D) + CH4→OH + CH3 has been carried out using the quasiclassical trajectory method(QCT) on a potential energy surface structured by Gonzalez et al. The integral cross sections(ICSs), differential cross sections(DCSs) and product rotational angular momentum polarization have been calculated. With the collision energy increasing, the ICS decreases. There is no threshold energy, because no barrier is found on the minimum energy path. The DCS results show that the backward and forward scatterings exist at the same time. With the collision energy increasing, the dominant rotation of the product changes from the right-handed direction to the left-handed direction in planes parallel to the scattering plane. In the isotopic effect study, the decrease of the mass factor weakens the polarization degree of the rotational angular momentum vectors of the products.     

Stereodynamics study of the exchange reaction O(~3P)+CH_4 →H+OCH_3

A new London-Eyring-Polanyi-Sato potential energy surface is employed in this work to study the stereo properties of the O(3P)+CH4 →H+CH3O reaction in its rovibrationally ground state using the quasiclassical trajectory method(QCT).Our calculations are performed at a range of collision energies,Ec=1.5eV～3.5eV,and the excitation function obtained by the QCT method accords well with the experimental data.The product rotational polarization is calculated,and the product shows a strong rotational polarization in the centre-of-mass coordinate system.The orientation of the product rotational angular momenta is sensitive to the increase in collision energy,and the alignment of the product rotational angular momenta shows some of the properties of the heavy heavy-light mass combination reactions.In the isotopic substituted reaction study,when the H atoms in methane are replaced by D atoms,the rotational polarization is obviously reduced.The polarization-dependent differential cross section is also studied by this QCT calculation to provide detailed information about the rotational alignment and orientation of the product.     

Stereodynamics study of the H′（^2S） ＋ NH（X^3∑-） 〉 N（4S） ＋ H2 reaction

The stereodynamics and reaction mechanism of the H′（^2S） ＋ NH （X^3∑^-） → N（^4S） ＋ H2 reaction are thoroughly studied at collision energies in the 0.1 eV-1.0 eV range using the quasiclassical trajectory （QCT） on the ground 4A″ potential energy surface （PES）. The distributions of vector correlations between products and reagents P（φr）, P（φr） and P（φr,φr） are presented and discussed. The results indicate that product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane; further, the product H2 presents different rotational polarization behaviors for different collision energies. Furthermore, four polarization-dependent differential cross sections （PDDCSs） of the product He are also calculated at different collision energies. The reaction mechanism is analyzed based on the stereodynamics properties. It is found that the abstraction mechanism is appropriate for the title reaction.