Dynamical Stereochemistry Research Articles

Low-energy stereodynamics in the ion–molecule reactions D+ + D2/HD and H+ + H2/HD: reagent vibrational excitation effect and mass factor effect

The low-energy chemical stereodynamics of these ion–molecule reactions D+ + D2 → D2 + D+, D+ + HD → DH + D+/D2 + H+, H+ + HD → H2 + D+/HD + H+ and H+ + H2 → H2 + H+ has been investigated by performing the quasi-classical trajectory calculations on the ground electronic state potential energy surface (11A′ PES). The polarization-dependent differential cross sections and the probability distributions of P(θ r ) and P(ϕ r ) have been calculated, compared and discussed within the center-of-mass frame and at the low collision energy of 100 meV. The calculation results indicate that the product scattering and the polarization of the product rotational angular momentum are sensitive to the reactant vibrational quantum number. Such sensitivity increases with the increasing value of mass factor. Moreover, the products from the reaction H+ + HD → HD + H+ show quite different scattering and polarization behaviors with reagent vibration excitation.

Strong laser field control of fragment spatial distributions from a photodissociation reaction

The notion that strong laser light can intervene and modify the dynamical processes of matter has been demonstrated and exploited both in gas and condensed phases. The central objective of laser control schemes has been the modification of branching ratios in chemical processes, under the philosophy that conveniently tailored light can steer the dynamics of a chemical mechanism towards desired targets. Less explored is the role that strong laser control can play on chemical stereodynamics, i.e. the angular distribution of the products of a chemical reaction in space. This work demonstrates for the case of methyl iodide that when a molecular bond breaking process takes place in the presence of an intense infrared laser field, its stereodynamics is profoundly affected, and that the intensity of this laser field can be used as an external knob to control it.

Effects of collision energy on the stereodynamics of the reaction O + H2+ → OH + H+

Quasi-classical trajectories calculations have been carried out to study the stereodynamics of the reaction O+H2+(v=0, j=0)→OH+H+ on the first excited-state potential energy surface (12A′) of Paniagua et al. (2014). The reaction probability for the total angular momentum J=0 and the integral cross section are presented at the collision energies of 0.1–1.2eV. Furthermore, the product rotational alignment factor 〈P2(j′·k)〉 has also been obtained. To show the collision-energy dependence on the chemical stereodynamics of the title reaction, the PDDCSs and the angular distributions of P(θr) and P(ϕr) are investigated. The results indicate that the product rotational angular momentum j′ is not only aligned, but also oriented along the positive y-axis. The stereodynamics of the reaction O+H2+→OH+H+ depend sensitively on the collision energy.

A New Reaction Path for the C+NO→CN+O Reaction: Effect of Reagent Rotation on the Stereodynamics on the 4A″ Potential-Energy Surface

The stereodynamics of the C+NO reaction is investigated at 0.06 eV by means of the quasiclassical trajectory method on a recent ab initio 4A″ potential energy surface (PES). The influences of rotation excitation (j = 0–3) on stereodynamics are discussed. The obtained stereodynamical information is compared with the previously reported results on the 2A' and 2A″ PESs to give a full insight into the chemical stereodynamics of the title reaction.

Exploring the stereodynamics of C(3P)+NO(X2)CO(X1+)+N(4S) reaction on 4A potential energy surface

Studies on the dynamical stereochemistry of the titled reaction are carried out by the quasi-classical trajectory (QCT) method based on a new accurate 4A potential energy surface constructed by Abrahamsson and coworkers (Abrahamsson E Andersson S, Nyman G, Markovic N 2008 Phys. Chem. Chem. Phys. 10 4400) at a collision energy of 0.06 eV. The distribution p(r) of the angle between k-j' and the angle distribution P(r in terms of k-k'-j' correlation have been calculated. Results indicate that the rotational angular momentum vector j' of CO is preferentially aligned perpendicular to k and also oriented with respect to the k-k' plane. Three polarization-dependent differential cross sections (2/)(d00/dt), (2/)(d20/dt), and (2/)(d22+/dt) have also been calculated. The preference of backward scattering is found from the results of (2/)(d00/dt). The behavior of (2/)(d20/dt) shows that the variation trend is opposite to that of (2/)(d00/dt), which indicates that j' is preferentially polarized along the direction perpendicular to k. The value of (2/)(d22/dt) is negative for all scattering angles, indicating the marked preference of product alignment along the y-axis. Furthermore, the influences of initial rotational and vibrational excitation on the reaction are shown and discussed. It is found that the initial vibrational excitation and rotational excitation have a larger influence on the alignment distribution of j' but a weaker effect on the orientation distribution of j' in the titled reaction. The influence of the initial vibrational excitation on the three polarization-dependent differential cross sections of product CO is stronger than that of the initial rotational excitation effect.

Quasiclassical state-to-state dynamics of the F + HCl reaction on a ground 12A′ potential energy surface

Quasi-classical trajectories have been evaluated to study the state-to-state dynamic for the title reaction on a recent DHTSN PES of the ground 12A′ electronic state [Deskevich et al., J. Chem. Phys. 124 (2006) 224303]. State resolved integral and differential cross sections (DCSs), as well as product rotational polarization, have been obtained for F+HCl (v=0, j=0)→Cl+HF(v′, j′) reaction at Ecol=10.0 and 50.0kcal/mol. Both the vibrational and the rotational distributions are found to be inverted, with the peaks locating at excited final states. At Ecol=10.0kcal/mol, the vibrational resolved DCSs are mainly directed backward and correspond to a simple direct-rebound mechanism. However, for Ecol=50.0kcal/mol, the HF(v′=0) products are preferentially backward-scattered, while the vibrationally excited HF(v′=1, 2, 3) are forward- scattered. These results can be interpreted by increasing of reactive collisions with high-b, which corresponds to a “stripping” dynamics. The P(θr) and P(Φr) distributions and the polarization parameters, a1-{1}, a0{2}, are also obtained to gain insights into the chemical stereodynamics of the title reaction. The HF rotational angular momentum has been found to be both aligned and oriented, and depends sensitively on the product rotational level. Difference in polarization behavior is discussed by means of the reactive mechanism.

Quasiclassical trajectory theoretical study on the chemical stereodynamics of the O(1D) + H2 → OH + H reaction and its isotopic variants (HD, D2)

The quasiclassical trajectory (QCT) method is used to study stereodynamic information about the reaction O (1D) + H2 → OH + H on the DK (Dobbyn and Knowles) (11A′) ab initio potential energy surface (PES). A wide scale of collision energy (Ec) 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), dσ00/dωt (0, 0) and dσ20/dωt(2, 0), and two angular distributions, P(θr) and P(φr) 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, D2) 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 the reaction N(4S) + H2 and its reverse reaction: Role of initial vibrational and rotational excitations in chemical stereodynamics

To investigate the effects of reagent vibrational and rotational states on the stereodynamical properties of the N(4S) + H2(v, j) → NH + H reaction and its reverse reaction of H(2S) + NH(v, j) → N(4S) + H2, we reported a detailed quasiclassical trajectory study using the 4A″ double many-body expansion potential energy surface and at the collision energy of 35 kcal/mol. The density distribution of P(θ r) as a function of the angle between \(\boldsymbol{k}\) and \(\boldsymbol{j^\prime} \), and that of P(ϕ r) as a function of the dihedral angle between the plane containing \(\boldsymbol{k}\)–\({\boldsymbol{k^\prime}} \) and the plane containing \(\boldsymbol{k^\prime}\)–\(\boldsymbol{j^\prime} \), the normal differential cross-sections as well as the averaged product rotational alignment parameter \(\left\langle {P_2 \left({\boldsymbol{j^\prime} \cdot \boldsymbol{k}} \right)} \right\rangle \) are calculated and reported. Comparison between the two reactions has showed that the degrees of alignment and orientation of products related to reagent rovibrational state have marked differences for the two reactive systems. The calculated average rotational alignment parameter \(\left\langle {P_2 \left({\boldsymbol{j^\prime} \cdot \boldsymbol{k}} \right)} \right\rangle \) as a function of the initial vibrational and rotational quantum numbers for the N(4S) + H2 and NH + H(2S) reactions, illustrating the dependence of the product alignment on initial vibrational and rotational excitations.

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 3A″ 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.

VECTOR CORRELATIONS AND PRODUCT POLARIZATIONS IN THE N(2D) + D2 → ND + D REACTIVE SYSTEM

The vector correlations between products and reagents of the N (2D) + D 2 reaction are investigated by employing quasi-classical trajectory (QCT) calculation on the accurate DMBE potential energy surface (PES) of the 2A″ state. Stereo-dynamic quantities, including the four generalized polarization-dependent differential cross-sections (PDDCSs), the angular distribution P(θr), the dihedral-angle distribution P(φr), as well as the product rotational angular distribution in the polar form of P(θr, φr), are calculated in the center-of-mass (CM) frame. The results indicate that the product rotational angular momentum j′ not only aligns along the y-axis, but also orients to the negative direction of the y-axis. The isotope effect in the context of chemical stereo-dynamics and influences of different versions of ground-state PESs on vector correlations are shown and discussed.

Influence of collision energy on cross section and stereodynamical properties for the reaction H + OCl → OH + Cl

The quasi-classical trajectory calculations are carried out for the reaction H+OCl→OH+Cl on the singlet ground state potential energy surface. The reaction probability for total angular momentum J=0 and the integral cross section as a function of collision energy are presented. Furthermore, the product rotational alignment <P2(j′·k)> has been obtained, and the value tends to decrease with the increasing of collision energy with fluctuations. To investigate the collision-energy-dependent effects on chemical stereodynamics, the four generalized polarization-dependent differential cross sections (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt) and (2π/σ)(dσ21−/dωt), the distribution P(θr) of the angle between j′–k and the angle distribution P(ϕr) in terms of k–k′–j′ correlation have also been calculated.

Stereodynamics of chemical reactions: quasi-classical, quantum and mixed quantum-classical theories

Abstract In this review, some benchmark works by Han and coworkers on the stereodynamics of typical chemical reactions, triatomic reactions H + D2, Cl + H2 and O + H2 and polyatomic reaction Cl+CH4/CD4, are presented by using the quasi-classical, quantum and mixed quantum-classical methods. The product alignment and orientation in these A+BC model reactions are discussed in detail. We have also compared our theoretical results with experimental measurements and demonstrated that our theoretical results are in good agreement with the experimental results. Quasi-classical trajectory (QCT) method ignores some quantum effects like the tunneling effect and zero-point energy. The quantum method will be very time-consuming. Moreover, the mixed quantum-classical method can take into account some quantum effects and hence is expected to be applicable to large systems and widely used in chemical stereodynamics studies.

Isotope effect of the stereodynamics for the reactions H(D) + OH(D) → O( 3P) + HH(D)

Studies on the dynamical stereochemistry of the title reactions were carried out by quasi-classical trajectory (QCT) method based on the lowest 3A′ electronically states [S. Rogers, D. Wang, A. Kuppermann, S. Wald, J. Phys. Chem. A 104 (2000) 2308]. The four polarization-dependent differential cross-section (PDDCSs) ( 2 π / σ ) ( d σ 00 / d ω t ) , ( 2 π / σ ) ( d σ 20 / d ω t ) , ( 2 π / σ ) ( d σ 22 + / d ω t ) and ( 2 π / σ ) ( d σ 21 - / d ω t ) are calculated in the center-of-mass frame, respectively. The distributions of the angle between k and j′ , P( θ r ), the dihedral angle P( ϕ r ), and the product rotational vectors in the form of polar plots P( θ r , ϕ r ) are also calculated. Furthermore, the influences of the isotope mass on the product polarization are shown and discussed. The results indicate that the PDDCSs are sensitive to the isotope effect. The degree of P( θ r ) and P( ϕ r ) distributions are presented an uptrend with the increase of the mass factor cos 2 β.

Stark-induced adiabatic Raman passage for preparing polarized molecules

We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H(2) molecule in its ground electronic state. Specifically, the H(2) (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to the z axis (uniaxial π-π Raman pumping). Similarly, H(2) (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along the z axis (σ(±)-σ(∓) Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ~16 GW/cm(2) for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ~12 and 60 mJ within a focused beam of diameter ~0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.

A quasiclassical trajectory analysis of stereodynamics of the H + FCl (v = 0 – 3, j = 0 – 3) → HCl + F reaction

The chemical stereodynamics for the title reaction are studied by the quasiclassical trajectory method. Employing the recent works of Deskevich, Hayes, Takahashi, Skodje, and Nesbitt (DHTSN) potential energy surface of the ground 12A′ electronic state, the present work calculates the polarization-dependent differential cross sections and the three angular distributions which describe the vector correlations among the product angular momentum j′ and the reagent and the product initial relative velocities k and k′. The effect of vibrational and rotational excitations for the reagent FCl and the influence of collision energies on the stereodynamical quantities are also investigated and discussed.

Chemical stereodynamics of the [formula omitted] reaction on the two lowest triplet electronic states

In this article, we apply the quasi-classical trajectory (QCT) method to study the reaction O ( 3 P ) + H 2 ( ν = 0 , j = 0 ) → OH + H on the 3A′ and 3A″ potential energy surfaces (PESs). Information of the vector correlations revealing the product alignment and orientation on the two different triplet PESs has been provided. The results of the calculations show that the products not only align strongly along the direction perpendicular to reagent initial relative vector k , but also orient along the direction of the negative y-axis, with stronger product polarizations being observed on the 3A″ PES at the collision energy smaller than 24 kcal/mol and on the 3A′ PES at the collision energy bigger than 24 kcal/mol. On both PESs, especially on the 3A″ PES, the products show preference for backward scattering which becomes weaker as collision energy increases.

Quasiclassical Trajectory Calculations of the Isotope Effect: Chemical Stereodynamics for the H(D) + FCl (v = 0–3,j = 0–3) → HCl(DCl) + F Reactions

Abstract A comparative quasiclassical trajectory study of the H + FCl (v = 0–3,j = 0–3) → HCl + F reaction and its isotope variant has been carried out to investigate the isotope effect from a chemical stereodynamics view point. Employing the recent DHTSN PES of the ground 12A′ electronic state [Deskevich et al., J. Chem. Phys.2006, 124, 224303], the present study calculated the angular distributions and the four polarization-dependent differential cross sections characterizing the vector correlations among the product angular momentum j′ and the reagent and the product initial relative velocities k and k′. The investigated collision energies are 20 and 40 kcal mol−1. The study revealed stronger product polarization behaviors in the heavier isotope variant which can be explained with the proposed impulse model for triatomic collision systems.

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.

Application of the sixth-order symplectic integration to the chemical stereodynamics for the reactions Li + H(D)F ( v = 0, j = 0) → LiF + H(D)

Studies on the dynamical stereochemistry of the Li + HF reaction and its isotopic variants have been performed using quasi-classical trajectory (QCT) method with the sixth-order symplectic integration on the AP2-PES which is produced by Aguado et al. [A. Aguado, M. Paniagua, M. Lara, O. Roncero, J. Chem. Phys. 107 (1997) 10085]. The polarization-dependent differential cross-sections (PDDCSs) have been calculated and compared. In addition, comparisons of the distributions P( θ r ), P( ϕ r ) and of the average rotational alignment factor 〈 P 2(cos θ r )〉 are given for the isotopic variants.

Theoretical study of stereodynamics for the O( 1D) + D 2 → OD + D reaction

A quasi-classical trajectory method (QCT) running on the 1A′ and 1A″ potential energy surfaces (PESs) given by Dobbyn and Knowles [A.J. Dobbyn, P.J. Knowles, Mol. Phys. 91 (1997) 1107] has been employed to study the dynamical stereochemistry of the chemical reaction O( 1D) + D 2 → OD + D, especially the vector correlations between products and reagents. The results indicate that product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane on both PESs, with different rotational polarization behaviors of product OD for the two PESs and for different collision energies. Calculations show that the alignment effect of products become weaker with an increase of the collision energy on the 1A′ PES but is not sensitive to the collision energy on the 1A″ PES. When the collision energy increases, the product OD mainly tends to the forward scattering on the 1A′ PES and displays a switch from the backward scattering to the forward one on the 1A″ PES. These differences are probably attributed to the different characteristics of the two PESs.