Narrow Results

The dynamical property of ground state CaBr formed in the reaction of Ca atom with CH₃Br has been studied with the quasi-classical trajectory method based on a constructed extended London-Eyring-Polanyi-Sato potential energy surface. In this paper, we report state-to-state distributions in the reaction of Ca with CH₃Br. They are vibrational distribution, rotational distribution, rotational alignments of the product CaBr, and reaction cross section, which are under detailed investigation. The vibrational distribution of CaBr clearly shows that the peak is located at v = 8 at collision energy E_col = 12.22 kcal/mol. The calculated results also show that the peak value of rotational population of the product CaBr is located at J = 50 at collision energy 12.22 kcal/mol. The reaction cross section increases with the increasing collision energy from 0.15 to 0.53 eV. The product rotational alignments deviate slightly from -0.5 and increase while the collision energy of reagent increase. By comparing with the experimental data, it can be found that the theoretical results closely agree with the experimental ones.

The nine-dimension quasi-classical trajectory (QCT) calculations have been carried out for the title reaction with a global potential energy surface (PES) constructed by Corchado and Espinosa-García (J Chem Phys106:4013, 1997). The detailed dynamics calculations cover the specific collision energies falling in the range of 0.62–3.04 eV, which are sufficient to fit the calculated reactive cross-sections into a barrier-type excitation function and to obtain the thermal rate constants. The present QCT rate constants are in good agreement with the recent quantum dynamics (QD) results, both of which are much lower than that of the previous variational transition state theory (VTST).

The stereodynamics of the title reaction on the ground 1 ¹A′ potential energy surface (PES) has been studied using quasi-classical trajectory (QCT) method. Collision energy of 6.4 kcal/mol is considered, and vector properties including angular momentum alignment distributions and polarization-dependent differential cross-sections (PDDCS) of the product OH are presented. Furthermore, the influence of reagent rotational excitation and vibrational excitation on the product vector properties has also been studied in the present work. The results indicate that the distribution of the P(θ_r) and P(ϕ_r) are sensitively affected by the rotational and vibrational excitation. The rotational excitation decreases the degree of alignment and orientation, while vibrational excitation increases the degree of alignment and orientation. The PDDCS (2π/σ)(dσ₂₀/dω_t) and (2π/σ)(dσ₂₂₊/dω_t) are sensitively influenced by rotational and vibrational excitations, while the PDDCS ((2π/σ)(dσ₀₀/dω_t)) and (2π/σ)(dσ_21-/dω_t) are not. The preference of forward scattering has been found from the results of PDDCS ((2π/σ)(dσ₀₀/dω_t)), which is in good agreement with the experimental results.

The first quasi-classical trajectory (QCT) calculation for the exothermic reaction Sr + CH₃Br is carried out based on a constructed London–Eyring–Polanyi–Sato (LEPS) potential energy surface (PES). By QCT calculation, the product SrBr vibration distributions are obtained. The result is in good comparison with the experimental one by Keijzer JF et al. [Chem. Phys.207:261, 1996]. Furthermore, the reaction product SrBr angular distribution and rotational alignment are also obtained. The products are dominantly forward-scattered and the alignment effect is obvious. Fast dynamics mechanism is proposed upon the calculation results.

Quasi-classical trajectory (QCT) calculations are carried out for the title reactions on the potential energy surface (PES) of Ho et al.¹ Our calculated integral cross-section values have been compared with the recent two quantum mechanics (QM) ones: they are close to those of one QM calculation in the high collision energy range, but they approach to another one in the low collision energy range. The product rotational alignments 〈P₂ (J' ⋅ K)〉 have also been calculated.

The stereodynamics of the title reaction on the ground electronic state X²A' potential energy surface (PES)¹ has been studied using the quasiclassical trajectory (QCT) method. The commonly used polarization-dependent differential cross-sections (PDDCSs) of the product and the angular momentum alignment distribution, P(θ_r) and P(Φ_r), are generated in the center-of-mass frame using QCT method to gain insight of the alignment and orientation of the product molecules. Influence of collision energy on the stereodynamics is shown and discussed. The results reveal that the distribution of P(θ_r) and P(Φ_r) is sensitive to collision energy. The PDDCSs exhibit different collision energy dependency relationship at low and high collision energy ranges.

Quasi-classical trajectory (QCT) method is used to study the stereo-dynamics of the title reaction on the ground 1 ¹A′ potential energy surface (PES). Differential cross-sections (DCSs) and alignments of the product rotational angular momentum for the reaction are reported. The influence of collision energy on the product vector properties is also studied in the present work. The distribution of angle between k and j′, P(θ_r), the distribution of dihedral angle denoting k-k′-j′ correlation, P(ϕ_r) ⋅ (2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t), (2π/σ)(dσ₂₂₊/dω_t) and (2π/σ)(dσ_21-/dω_t) have been calculated in the center of mass frame, respectively.

Theoretical study on stereodynamics for the title reaction as well as its isotopic effects has been studied via QCT calculations on the ground X²A′ state of ab initio potential energy surface according to the study by Zanchet et al. Four polarization-dependent generalized differential cross-sections PDDCSs ((2π/σ) (dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t)), (2π/σ)(dσ₂₂₊/dω_t), (2π/σ)(dσ_21-/dω_t), and the distributions of P(θ_r) and P(φ_r) that denotes the correlations of k-j′ and k-k′-j′ are presented in this work. Product angular distribution and rotational polarization have been analyzed at different collision energies and compared with C+OH reaction. Product angular distribution shows strong forward scattering at low collision energy and becomes more symmetric with forward and backward scattering with the increasing collision energy. The alignment and orientation of product angular momentum presents a different behavior with collision energy, the former one increases monotonically with collision energy, whereas the latter one shows first decreasing and then increasing behavior, which have been analyzed in the present paper. Product rotational polarization for C+OD is weaker than that for C+OH, which is mainly due to the mass factor and zero point energy of C+OD.

The chemical reaction dynamics between Sr atom and CF₃Br has been studied by using the method of quasi-classical trajectory calculation on the London-Eyring-Polanyi-Sato potential energy surface. The vibrational distribution, reaction cross section and rotational alignment of the product SrBr have been calculated. The calculated results indicate that the cross section of this reaction decreases and the product rotational alignment increases with the increase in collision energy. It has been found that low collision energy generates the abstraction reaction whereas high collision energy leads to the insertion. The conclusions in this paper agree well with experimental data and some relative theoretical results as well.

Quasiclassical trajectory (QCT) calculations have been performed to investigate the reaction dynamics of the title reactions at a state-to-state level. The recently developed adiabatic potential energy surfaces (PESs) of the two triplet electronic states of 1³A″ and 1³A′ (Gómez-Carrasco S. et al., J Chem Phys121:4605, 2004; J Chem Phys123:114310, 2005) are employed in the present QCT calculations. Product vibrational and rotational state distributions have been calculated at three collision energies of 0.5, 0.7 and 0.9 eV. The product vibrational state distributions are found to be Gaussian distributions. Both the vibrational and rotational state distributions depend clearly on the isotope substitution, electronic PESs and collision energies. The observed phenomena are probably attributed to the competition of direct and indirect reactions.

Quasi-Classical Trajectory (QCT) calculations have been carried out to study the stereodynamics of the reactions N + NH → N₂ + H and isotopic effects on the product polarization at collision energies of 10.0 kcal/mol and 25.0 kcal/mol which proceed on the Double-Many-Body-Expansion (DMBE) potential energy surface. The distribution of dihedral angle P(ϕ_r), and the distribution of angle between k and j′, P(θ_r) are discussed in detail. Furthermore, four generalized polarization dependent differential cross sections (PDDCSs) (2π/σ)(dσ₀₀/dω), (2π/σ)(dσ₂₀/dω), (2π/;σ)(dσ₂₂₊/dω), and (2π/σ)(dσ_{21 -}∕dω) are presented. The results reveal that isotope effect plays an important role for P(ϕ_r) and P(θ_r) distribution, and the PDDCSs exhibit similar collision energy dependency relationship at low and high collision energies.

A new London–Eyring–Polanyi–Sato (LEPS) potential energy surface (PES) is employed in this work to study the stereo properties for the abstraction reaction of hydrogen with methane at its rovibrationally ground state using the quasiclassical trajectory method (QCT). A "quasi-triatomic" approximation is used to treat the CD₃ group of CD₄ as a pseudoatom. The calculated excitation function of the title reaction can give a good agreement to most experimental and theoretical data at collision energies (E_c =1.5 ~ 2.5 eV). Further investigation of the product HD in reaction H + CD₄(v = 0, j = 0) → HD + CD₃ and D + CH₄(v = 0, j = 0) → HD + CH₃ shows the dependence of the product rotational polarization on collision energies and mass factor, but P(θ_r) is not sensitive to both the collision energies and the mass factor.

The quasi-classical trajectory (QCT) calculations have been carried out for the reaction N + NH (v = 0–3, j=0) → N₂ + H on the ground state of double many-body expansion (DMBE) potential energy surface [Caridade, PJSB, Poveda LA, Rodrigues SPJ, Varandas AJC, J Phys Chem A111:1172, 2007]. The influence of reagent vibrational excitation on reaction probability for total angular momentum J = 0 and integral cross section (ICS) at collision energies ranging from 0.1 eV to 1.0 eV has been investigated. The reaction probability tends to decrease with increasing collision energy and increase with the rising of initial vibration state, although some fluctuations appear. The ICS declines monotonously with the increase of collision energy and v. The product rotational alignment factor 〈P₂(j′•k)〉 has also been calculated, and its value has a declining trend with the increase of collision energy. In spite of that, the results still show that the product is highly aligned. In addition, the vibrational excitation effect on the product polarization has also been studied. All the distributions of P(ϕ_r), P(θ_r), and the generalized polarization dependent differential cross sections indicate dependent behaviors on v.