Three-dimensional trajectory study of the I + HI → IH + I, H + I2 reactions

The quasiclassical trajectory calculation of the I + HI collision is performed in order to study the exchange and endothermic reaction channels. The rate constant of the exchange reaction I′ + HI → HI′ + I is found to be equal to 7.7 × 10¹¹ cm³/mol s at room temperature of 300 K. The study of the endothermic reaction I + HI → H + I₂ shows that it takes place only in configurations with large bend angles. Due to the non-collinear character of this reaction its threshold (2 eV) exceeds significantly the threshold of the minimal energy (collinear) reaction path (1.55 eV).     

Influence of the potential energy surface on the reaction cross section: the K + HF → KF + H system

The effect of the potential energy surface on the K + HF → KF + H cross section has been studied using reasonable Sorbie-Murrell (bent saddle point) and LEPS (collinear saddle point) potential energy surfaces (PESs). Trajectory calculations for selected initial conditions (translational energies, rovibrational levels (v, J) of HF, as well as initial parallel or perpendicular alignments between the HF rotational angular momentum and the reactants relative velocity vectors) have been performed on these PESs to compare them with experiments. The Sorbie-Murrell and LEPS-4 PESs lead to steric effect ratio results quite close to the experimental ones, once the error margins are included. The resllts point towards a bent K-F-H saddle point although the PES is very isotropic. This could explain why experimental determinations lead to suggest a collinear saddle point. The K + HF → KF + H reaction exhibits an enormous vibrational enhancement of reactivity with one quantum HF vibrational excitation, even at translational energies well above the HF(v=0) threshold, where tunnelling effect contribution to reactivity can be neglected. This behaviour has not been reproduced in the trajectory calculations and no satisfactory explanation has been obtained for this fact. Nevertheless, the HF(v=1)/HF(v=0) cross section ratio at translational energies not far from the HF(v=0) threshold and the relative cross section for HF(v=0) have been satisfactorily descibed. In what regards rotation, the best theoretical results are those corresponding to the Sorbie-Murrell PES (the cross section increases with J), although important differences with experiment appear for the J = 0–3 interval at the lower translational energy values considered (0.54 and 0.77 eV).     

Self-consistent-field potential energy surface in three dimensions for the Cl + H2 → ClH + H chemical reaction

Non-empirical self-consistent-field calculations have been carried out for 38 points on the potential surface for the Cl + H₂ → ClH + H chemical reaction. A basis set of seven s, five p, and one d functions on chlorine and three s and one p on each hydrogen atom was used. The least energy path occurs for the linear Cl---H---H arrangement. A much higher barrier is found for the approach of Cl along the H---H perpendicular bisector. The linear barrier height is predicted to be 26.2 kcal/mole and the saddle point occurs for R(Cl---H) ≈ 1.46 Å, R(H---H) ≈ 0.94 Å. The experimental activation energy is 5.5 kcal/mole. It seems likely that a general feature of the Hartree-Fock approximation is an overestimation of barrier heights. The exothermicity is calculated to be −6.7 kcal/mole, compared to the near Hartree-Fock result −2.3 kcal/mole and experiment −3.0 kcal/mole.     

The effect of reagent translational energy in the reaction O(D2) + H2 → OH(Π) + H

Quasiclassical trajectory calculations have been performed to determine the effect of reactant collision energy on product state distributions in the reaction O(¹D) + H₂ → OH(²Π) + H. The product vibrational distribution becomes more excited as the collision energy is increased. This is not due to an increase in the cross section for collinear abstraction. A detailed analysis has shown that strong O---H₂ repulsion, which occurs during the insertion of the O into the H---H bond, converts the kinetic energy of the reacting system to vibrational motion of the intermediate.     

Cl+HD反应产物的极化与态分布

利用准经典轨线理论,在BW2和G3两个势能面上,研究了Cl+HD反应的动力学.计算结果表明,产物的转动取向对势能面及反应体系的质量因子非常敏感.在BW2势能面上,计算的两个产物的转动取向强于在G3势能面上计算的结果,而无论是在BW2势能面上还是在G3势能面上,DCl产物的取向都强于HCl产物的取向.计算结果还表明,在不同的势能面上反应物的转动激发对反应的影响有着显著的不同.在BW2势能面上,反应物的初始转动激发有利于Cl+HD反应的进行;而在G3势能面上,反应物的初始转动激发消弱了反应的反应性.     

Theoretical analysis of the O + CS(0) → CO(υ′)+ S reaction by the two half-collisions model

A theoretical analysis of the O + CS → CO + S reaction is presented. It is shown that the experimental CO vibrational distribution can be explained by a collinear O + CS reaction which proceeds via the lowest triplet OCS electronic state.     

氢原子共线交换反应的动力学计算I.Cl与HCl反应几率的振荡现象研究

我们利用超球坐标对共线Cl+HCl(V-3)→ClH(V'≤3)+Cl作了一维精确量子计算,计算所用势能面是LEPS型,Et=-3.23KJ/mol, 得到了态态反应几率等动力学信息, 通过分析结果发现, 反应是振动绝热的, 即以对角(V'-V')反应几率为主,非对角(V' V')反应几率小于0.1, 反应几率随总能量表现出强裂地振荡, 在有阱的势能面上动力学共振增强。     

Quasiclassical trajectory study of the Cl + Hl → HCl + I reaction

Monte Carlo quasiclassical trajectory calculations have been carried out for the reaction Cl + Hl → HCl + I for 300, 1000, and 2000 K. A semi-empirical potential-energy surface (London equation) was obtained by “transfering” parameters from surfaces computed for other reaction systems. The computed results are in general accord with experimental measurements. Thermal rate coefficients, differential scattering cross sections, and product vibrational and rotational distributions were computed for the three temperatures. Angular scattering distributions are in agreement with experiment only at elevated temperatures.     

Ab initio molecular orbital study on the gas phase SN2 reaction F + CH3Cl → CH3F + Cl

Ab-initio molecular orbital (MO) and direct ab initio dynamics calculations have been applied to the gas phase S_N2 reaction F⁻ + CH₃Cl → CH₃F + Cl⁻. Several basis sets were examined in order to select the most convenient and best fitted basis set to that of high-quality calculations. The Hartree–Fock (HF) 3−21+G(d) calculation reasonably represents a potential energy surface calculated at the MP2/6−311++G(2df,2pd) level. A direct ab initio dynamics calculation at the HF/3−21+G(d) level was carried out for the S_N2 reaction. A full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculation. Total energies and gradients were calculated at each time step. Two initial configurations at time zero were examined in the direct dynamics calculations: one is a near collinear collision, and the other is a side-attack collision. It was found that in the near collinear collision almost all total available energy is partitioned into two modes: the relative translational mode between the products (40%) and the C − F stretching mode (60%). The other internal modes of CH₃F were still in the ground state. The lifetimes of the early- and late-complexes F⁻ … CH₃Cl and FCH₃ … Cl⁻ are significantly short enough to dissociate directly to the products. On the other hand, in the side-attack collision, the relative translation energy was about 20% of total available energy.     

Integral and differential cross sections for the heavy-light-heavy cihci reaction. A quantum mechanical study within the infinite order sudden approximation

In this communication we present quantum mechanical integral and differential cross sections for the reaction HCl(ν_i = 0) + Cl′ → HCl′ + Cl. The calculations employed the the infinite order sudden approximation. The characteristic oscillations encountered in collinear calculations were still apparent in three dimensions.     

Quantum Dynamics of Li+HF/DF Reaction Investigated by a State-to-State Time-dependent Wave Packet Approach

Using the reactant coordinate based time-dependent wave packet method, on the APW potential energy surface, the differential and integral cross sections of the Li+DF/HF(v=0, j=0, 1) reactions were calculated over the collision energy range from the threshold to 0.25 eV. The initial state-specified reaction rate constants of the title reaction were also calculated. The results indicate that, compared with the Li+DF reaction, the product LiF of Li+HF reaction is a little more rotationally excited but essentially similar. The initial rotational excitation from j=0 to 1 has little effect on the Li+DF reaction. However, the rotational excitation of DF does result in a little more rotationally excited product LiF. The different cross section of both reactions is forward biased in the studied collision energy range, especially at relatively high collision energy. The resonances in the Li+HF reaction may be identifiable as the oscillations in the product ro-vibrational state-resolved integral cross sections and backward scattering as a function of collusion energy. For the Li+HF reaction, the rate constant is not sensitive to the temperature and almost has no change in the temperature range considered. For the Li+DF reaction, the rate constant increase by a factor of about 10 in the temperature range of 100?300 K. Brief comparison for the total reaction probabilities and integral cross section of the Li+HF reaction has been carried out between ours and the values reported previously. The agreement is good, and the difference should come from the better convergence of our present calculations.     

Planar study of H2O+Cl<-->HO+HCl reactions

The first four dimensional (4D) quantum scattering calculations on the tetra-atomic H2O+Cl<-->HO+HCl reactions are reported. With respect to a full (6D) treatment, only the planar constraint and a fixed length for the HO spectator bond are imposed. This work explicitly accounts for the bending and local HO stretching vibrations in H2O, for the vibration of HCl and for the in-plane rotation of the H2O, HO and HCl molecules. The calculations are performed with the potential energy surface of Clary et al. and use a Born-Oppenheimer type separation between the motions of the light and the heavy nuclei. State-to-state cross sections are reported for a collision energy range 0-1.8 eV measured with respect to H2O+Cl. For the H2O+Cl reaction, present results agree with previous (3D) non planar calculations and confirm that excitation of the H2O stretching promotes more reactivity than excitation of the bending. New results are related to the rotation of the H2O molecule: the cross sections are maximal for planar rotational states corresponding to 10相似文献   

Searching for resonances in the reaction Cl+CH4-->HCl+CH3: quantum versus quasiclassical dynamics and comparison with experiments

A quantum-mechanical (QM) and quasiclassical trajectory (QCT) study was performed on the title reaction, using a pseudotriatomic ab initio based surface. Probabilities and integral cross sections present some clear peaks versus the collision energy E(col), which we assign to Feshbach resonances of the transition state, where the light H atom oscillates between the heavy Cl and CH(3) groups. For ground-state reactants, reactivity is essentially of quantum origin (QCT observables and oscillations are smaller, or much smaller, than QM ones), and the calculated integral cross section and product distributions are in reasonable agreement with the experiment. The reaction occurs through an abstraction mechanism, following both a direct and an indirect mechanism. The quasiclassical trajectory calculations show the participation of a short-lived collision complex in the microscopic reaction mechanism. Finally, QCT differential cross sections of Cl+CH(4)-->HCl (nu(')=0 and 1)+CH(3) oscillate versus E(col), whereas experimentally this only occurs for HCl (nu(')=1). This theoretical result and other oscillating properties found here could, however, be related to the existence of a Feshbach resonance for the production of HCl (nu(')=1), as suggested by experimentalists.     

Quantum and quasiclassical studies of the O(3P)+HCl-->OH+Cl(2P) reaction using benchmark potential surfaces

We have performed quantum mechanical (QM) dynamics calculations within the independent-state approximation with new benchmark triplet A" and A' surfaces [B. Ramachandran et al., J. Chem. Phys. 119, 9590 (2003)] for the rovibronic state-to-state measurements of the reaction O(3P)+HCl(v=2,j=1,6,9)-->OH(v'j')+Cl(2P) [Zhang et al., J. Chem. Phys. 94, 2704 (1991)]. The QM and experimental rotational distributions peak at similar OH(j') levels, but the QM distributions are significantly narrower than the measurements and previous quasiclassical dynamics studies. The OH(low j) populations observed in the measurements are nearly absent in the QM results. We have also performed quasiclassical trajectory with histogram binning (QCT-HB) calculations on these same benchmark surfaces. The QCT-HB rotational distributions, which are qualitatively consistent with measurements and classical dynamics studies using other surfaces, are much broader than the QM results. Application of a Gaussian binning correction (QCT-GB) dramatically narrows and shifts the QCT-HB rotational distributions to be in very good agreement with the QM results. The large QCT-GB correction stems from the special shape of the joint distribution of the classical rotational/vibrational action of OH products. We have also performed QM and QCT calculations for the transition, O+HCl(v=0,T=300 K)-->OH(v'j')+Cl from threshold to approximately 130 kcal mol(-1) collision energy as a guide for possible future hyperthermal O-atom measurements. We find in general a mixed energy release into translation and rotation consistent with a late barrier to reaction. Angular distributions at high collision energy are forward peaked, consistent with a stripping mechanism. Direct collisional excitation channel cross sections, O+HCl(v=0,T=300 K)-->O+HCl(v'=1), in the same energy range are large, comparable in magnitude to the reactive channel cross sections. Although the (3)A" state dominates most collision processes, above approximately 48 kcal mol(-1), the (3)A' state plays the major role in collisional excitation.     

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     

An ab initio study of the Cl(P)+C2H6→C2H5+HCl abstraction reaction

Electronic energies, geometries, and harmonic vibration frequencies for the reactants, products, and transition state for the Cl(³P)+C₂H₆→C₂H₅+HCl abstraction reaction were evaluated at the HF and MP2 levels using several correlation consistent polarized-valence basis sets. Single-point calculations at PMP2, MP4, QCISD(T), and CCSD(T) levels were also carried out. The values of the forward activation energies obtained at the MP4/cc-pVTZ, QCISD(T)/cc-pVTZ, and CCSD(T)/cc-pVTZ levels using the MP2/cc-pVTZ structures are equal to −0.1, −0.4, and −0.3 kcal/mol, respectively. The experimental value is equal to 0.3±0.2 kcal/mol. We found that the MP2/aug-cc-pVTZ adiabatic vibration energy for the reaction (−2.4 kcal/mol) agrees well with the experimental value −(2.2–2.6) kcal/mol. Rate constants calculated with the zeroth-order interpolated variational transition state (IVTST-0) method are in good agreement with experiment. In general, the theoretical rate constants differ from experiment by, at most, a factor of 2.6.     

Substantial velocity dependence of rotationally inelastic collision cross sections in Li2—Xe

A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ_ji,Δ(ν_r) for rotationally inelastic collisions from level j_i to j_i + Δν₁ = 8,22,42) in ⁷Li^*₂ A ¹Σ⁺_u)—Xe. The σ_jν^±2(ν_r) are strongly attenuated at a smaller ν_r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ_jiΔ = ν_r⁻ⁿ (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited.     

Cl+HCl非反应截面和速率常数的TST-CEQ研究Ⅲ

本文将TST-CEQ方法推广用于计算非反应弛豫速率和平均截面, 并以Cl+HCl反应为例作了计算, 与文献结果比较表明, 这种推广是可行的, 此外, 还给出了该体系反应和非反应一维态态速率常数; 结果发现, 低温时非反应弛豫速率大于反应速率; 高温时两种通道速率相近, 表现了反应的竞争机理。     

Absolute balmer line and NH(c Π→b Σ, 0-0) vibrational band emission cross sections from NH3 molecules excited by electron impact

The absolute Balmer line emission cross sections are determined in the processes of the electron impact dissociative excitation of ammonia. The optical excitation functions measured for these lines were investigated in the energy range 50–500 eV and normalized by the He benchmark procedure. The molecular continuum contribution has been eliminated from the obtained data. After that, the measured data have been corrected with the collection efficiency factor F to compensate the loss of optical signal due to non-thermal energies of the H excited fragments. The results for kinetic energy distribution functions for the ammonia molecules have been used for the F determination. The optical emission cross sections are determined with the accuracy of ± 15%. The cross sections for the NH(c ¹Π→b ¹Σ⁺, 0-0) vibrational band have also been determined with an accuracy of ± 25%.     

辛准经典轨迹法研究Cl+H2反应

用辛准经典轨迹法模拟了Cl+H2反应在mBW2势能面上的动力学行为。研究了各种初始条件下的反应碰撞截面,产物的能量分配,角度分布和态分布。另外,我们还比较了反应物的三种能量形式(平动能,转动能和振动能)对反庆的有效性。