Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

反应(Cl+HBr→HCl+Br和Cl+HBr→BrCl+H)机理和速率的密度泛函理论研究

用密度泛函理论(DFT)B3LYP方法,在6-311G**基组下,计算研究了反应Cl+HBr→HCl+Br和Cl+HBr→BrCl+H的机理,求得的各过渡态均通过振动分析加以确认.运用求得的反应活化能,以及不同温度下过渡态和反应络合物的配分函数,借助绝对反应速率理论求得50～1500K的反应速率常数.     

Br2+2HI=2HBr＋I2应机理的密度泛函理论

用密度泛函理论(DFT)B3LYP方法，取3-21G**基组研究了气相反应Br2＋2HI=2HBr＋I2的机理，求得一系列四中心和三中心的过渡态.双分子基元反应Br2＋HI→HBr＋IBr和IBr＋HI→I2＋HBr的活化能(81.02和121.08 kJ•mol－1)小于Br2、HI和IBr的解离能(249.21、320.16和232.42 kJ•mol－1)，故从理论上证明了标题反应将优先以分子与分子作用形式分两步完成.同时发现I原子与Br2分子反应生成较稳定的IBr2是一个无能垒过程，IBr2分解为IBr和Br原子的能垒为70.88 kJ•mol－1.     

Theoretical Study on the Reaction Mechanism of F2 ＋ 2HBr = 2HF ＋ Br2

1 INTRODUCTION The replacement reactions between halide and hy- drogen halide, or halide and halide are basic reac- tions in chemistry. Goldfinger et al. have speculated by experiment that the gas reaction between chlorine and hydrogen bromide might be a two-step intermo- lecular reaction[1, 2]. But gas reactions between other halides and hydrogen halides haven’t been reported experimentally so far. About theoretical investiga- tion, colinearity quantum mechanics, vibrational tran- sitio…     

Br2+Cl2=2BrCl反应机理的理论和实验研究

用(U)MP2方法, 取6-311G*基组, 研究了反应Br2+Cl2=2BrCl的机理, 求得四中心和三中心的过渡态, 通过比较反应通道的活化能的大小, 得到如下结论: 双分子基元反应的最小活化能小于Cl2和Br2的离解能, 在没有光引发的条件下, 标题反应将以分子与分子作用形式完成; 若有光引发, Br2或Cl2先解离成原子, 再经过Br原子与Cl2反应或Cl原子与Br2反应, 能较快完成标题反应. 分别测定了光照和避光两种条件下的反应体系在412 nm处吸光度的变化, 证实了理论研究的结果.     

Collinear quantum mechanical probabilities and rate constants for the Br + HCl(ν = 2, 3, 4) reaction using hyperspherical coordinates

Calculations of quantum mechanical probabilities and rate constants for the collinear reaction Br + HCl(ν = 2,3,4) → BrH + Cl, Br + HCl(ν < ν) were performed using hyperspherical coordinates. Removal of vibrationally excited HCl proceeds mainly by reaction to a nearly degenerate HBr state. Processes for which a large change in the internal enery occurs have low probabilities.     

CH2BrCl在265 nm光解产生的氯甲基自由基的振动内能

利用离子速度影像技术研究了CH2BrCl在265nm附近的激光光解.利用2+1共振增强多光子电离分别获得光解产物Br(2P1/2)和Br(2P3/2)的离子速度图像,从而得出Br(2P1/2)和Br(2P3/2)的速度分布,以及光解碎片的总平动能分布.据此,运用角动量守恒碰撞模型获得了解离氯甲基自由基(·CH2Cl)的振动内能分布.研究结果表明:CH2BrCl+hv→Br(2P1/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v4、v3+v4、v2+v4和v2+v6;CH2BrCl+hv→Br(2P3/2)+CH2Cl通道产生的氯甲基自由基中被激发的振动模主要是v2+v6、v1+v3、v2+v5、v2+v3+v5和v1+v5;母体分子CH2BrCl在吸收光解光子后除有v5(CBrstretch)振动模被激发外,还有v7(CH2a-stretch)等其它振动模也被激发.     

A theoretical investigation of the feasibility of Tannor-Rice type control: application to selective bond breakage in gas-phase dihalomethanes

Within the B? absorption band of CH(2)BrCl, we theoretically analyze the laser-induced control of the Br/Cl branching ratio, Br + CH(2)Cl ← CH(2)BrCl → CH(2)Br + Cl, with CH(2)BrCl initially in its vibrational ground state. For weak-field excitation, the Br/Cl branching ratio increases as a function of wavelength, however, for wavelengths below 180 nm the branching ratio cannot be made smaller than 0.4. Using optimal control theory, we show that the branching ratio can be made significantly less than 0.4, only when very strong fields are employed. Thus, the present work strongly suggests that a Tannor-Rice type laser control mechanism for selective bond breakage in CH(2)BrCl cannot take place without accompanying photoionization.     

Studies on the Reaction Mechanism of Br2 ＋ I2 = 2IBr

1 INTRODUCTION Interhalogen compounds have played an impor- tant role in environment and chemical engineering production. During the course of ozone exhaustion induced by sunlight in polar region, Br2, BrCl and HOBr are all precursors of Br atom[1]. Lately, scien- tists have detected that the content of BrCl in polar region sunlight was 35 ppt, larger than that of Br2 (25 ppt). Previous studies suggested that the con- centration of BrCl and O3 exhibits obvious negative correlation: w…     

State-to-state quantum dynamics of the H + HBr reaction: competition between the abstraction and exchange reactions

Quantum state-to-state dynamics for the H + HBr(υ(i) = 0, j(i) =0) reaction was studied on an accurate ab intio potential energy surface for the electronic ground state of BrH(2). Both the H + HBr → H(2) + Br abstraction reaction and the H' + HBr → H'Br + H exchange reaction were investigated up to a collision energy of 2.0 eV. It was found that the abstraction channel is dominant at lower collision energies, while the exchange channel becomes dominant at higher collision energies. The total integral cross section of the abstraction reaction at a collision energy of 1.6 eV was found to be 1.37 A?(2), which is larger than a recent quantum mechanical result (1.06 A?(2)) and still significantly smaller than the experimental value (3 ± 1 A?(2)). Meanwhile, similar to the previous theoretical study, our calculations also predicted much hotter product rotational state distributions than those from the experimental study. This suggests that further experimental investigations are highly desirable to elucidate the dynamic properties of the title reactions.     

Reaction products with internal energy beyond the kinematic limit result from trajectories far from the minimum energy path: an example from H + HBr --> H2 + Br

The importance of reactive trajectories straying far from the minimum energy path is demonstrated for the bimolecular reaction H + HBr --> H2(v', j') + Br at 53 kcal/mol collision energy. Product quantum state distributions are measured and calculated using the quasi-classical trajectory technique, and the calculations indicate that highly internally excited H2 products result from indirect reactive trajectories with bent transition states. A general argument is made suggesting that reaction products with internal energy exceeding a kinematic constraint can, in general, be attributed to reactive collisions straying far from the minimum energy path.     

A comparison of two-dimensional and three-dimensional trajectory calculations in thermal HBr2 and H2Br systems

Two-dimensional (2D) and three-dimensional (3D) quasiclassical trajectory calculations on H + Br₂ at 300°K and H + HBr at 1000°K are reported. Angular scattering, energy disposal, and impact parameter distributions for reactive collisions are compared after removal of phase-space factors (dimensionality bias) as a means of examining the similarities and differences in the dynamic bias in 2D and 3D. Qualitatively, for all reactive processes studied, the 3D trajectory calculated distributions are reproduced by the phase-space adjusted 2D trajectory data. Thus the surprisal of these angular scattering, energy disposal, and impact parameter distributions is dimensionally invariant, and the same dynamic bias appears in 2D and 3D. A systematic method for converting 2D reaction probabilities and maximum reactive impact parameters into 3D rate coefficients is presented. We find that trajectory calculated 3D rate coefficients may in general differ markedly from those derived from 2D trajectory data. In particular, the surprisal associated with rate coefficients depends on dimensionality for the H + HBr → H₂ + Br reaction, but is invariant for the H′ + HBr → H′Br + Br and H + Br₂ → HBr + Br reactions.     

Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl

The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH2BrCl) in the region of 85,320-88,200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0-1400 cm-1 above the adiabatic ionization energy (IE) of CH2BrCl, the Br-C-Cl bending vibration progression (nu1+=0-8) of CH2BrCl+ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400-2600 cm-1 above the IE(CH2BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH2BrCl+(A 2A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH2BrCl)=85,612.4+/-2.0 cm-1 (10.6146+/-0.0003 eV) and the bending frequencies nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->CH2Cl++Br+e-, in the energy range of 11.36-11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH2Cl+)=11.509+/-0.002 eV. Combining the 0 K AE(CH2Cl+) and IE(CH2BrCl) values obtained in this study, together with the known IE(CH2Cl), we have determined the 0 K bond dissociation energies (D0) for CH2Cl+-Br (0.894+/-0.002 eV) and CH2Cl-Br (2.76+/-0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH2BrCl), AE(CH2Cl+), IE(CH2Cl), D0(CH2Cl+-Br), and D0(CH2Cl-Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.     

Cyclic transport of Fe3+ As H[FeCl4] and H[FeBr4] through a dibutyl ether-benzene membrane

Cyclic transport of Fe³⁺ as H[FeX₄], where X is Cl or Br, across solvent-type liquid membranes has been demonstrated. H[FeCl₄] was transported from HCl into HBr across a dibutyl ether—benzene mixture. In HBr the transported species reacted to H[FeBr₄], which moved out to the HCl side against the concentration gradient of Fe³⁺. On the HCl side it was reconverted into H[FeCl₄]. This continued till equilibrium was achieved. Likewise, Fe³⁺, present as H[FeBr₄] in HBr, migrated from HBr into HCl and then back to HBr across the same membrane.     

Rate constants calculation of hydrogen abstraction reactions CH3CHBr + HBr and CH3CBr2 + HBr

Dual‐level direct dynamics method is used to study the kinetic properties of the hydrogen abstraction reactions of CH₃CHBr + HBr → CH₃CH₂Br + Br (R1) and CH₃CBr₂ + HBr → CH₃CHBr₂ + Br (R2). Optimized geometries and frequencies of all the stationary points and extra points along the minimum‐energy path are obtained at the MPW1K/6‐311+G(d,p), MPW1K/ma‐TZVP, and BMK/6‐311+G(d,p) levels. Two complexes with energies less than that of the reactants are located in the entrance of each reaction at the MPW1K/6‐311+G(d,p) and MPW1K/ma‐TZVP levels, respectively. The energy profiles are further refined with the interpolated single‐point energies method at the G2M(RCC5)//MPW1K/6‐311+G(d,p) level of theory. By the improved canonical variational transition‐state theory with the small‐curvature tunneling correction (SCT), the rate constants are evaluated over a wide temperature range of 200–2000 K. Our calculations have shown that the radical reactivity decreases from CH₃CHBr to CH₃CBr₂. Finally, the total rate constants are fitted by two modified Arrhenius expression. © 2012 Wiley Periodicals, Inc.     

Hydrogen abstraction by fluorine atoms: F + HX and F + DX (X = I,Br, Cl)

Absolute reaction rates for F + HX and F + DX (X = I, Br, Cl) have been obtained by monitoring the rise time of HF (DF) vibrational fluorescence following multiphoton dissociation of SF₆ in mixtures of HX (DX) and argon. The cross sections for reaction are, in units of 10^?16 cm², 4.37, 5.26, and 1.16 for HI, HBr, and HCl, respectively. The isotope effects k_HX/k_DX, are 1.29 ± 0.14, 1.29 ± 0.18, and 1.38 ± 0.29, respectively.     

F2＋2HI=2HF＋I2反应机理的研究

根据氯离子型层状复合氢氧化物(LDH-Cl)制备过程中溶液浓度变化的监测结果和不同反应进程时产物的EDS、IR、XRD、TEM、TG-DTA表征结果,研究了合成LDH-Cl的共沉淀反应动力学特征及机理.实验结果表明, LDH-Cl的生成符合多核层表面反应动力学模型;反应过程中LDH的晶胞参数c从2.421 nm变为2.399 nm,通道高度h由0.3321 nm减小为0.3228 nm,粒子直径Da由6.40 nm增大为15.16 nm, Dc由7.43 nm增大到10.93 nm,纵横比由0.86增大为1.39; IR和TG-DTA特征变化表明了层板对阴离子作用的强度和层板的结构稳定性随反应进程而提高.     

Exchange reactions of hydrogen halides with hydrogenic atoms

Calculations on the D + HBr → DBr + H and D + HI → DI + H reactions are reported. A three-dimensional, quantum-dynamical approximation is used which involves applying the energy sudden approximation to the entrance channel hamiltonian and the centrifugal sudden approximation to the exit channel hamiltonian. Results of integral and differential cross sections, rate coefficients and rotational distributions are presented. Diatomics-in-molecules potential-energy surfaces have been used in the computations. The HBrH potential has been optimesed so that the calculated room-temperature rate coefficient agrees with experiment. This potential has a barrier height of 0.237 eV. Rate coefficient computations for the four reactions H′ + H″ Cl → - H′Cl + H″ (H′, H″ = H or D) are also reported. These results, for a LEPS surface, agree well with those obtained in quasiclassical trajectory and variational transition state theory calculations.     

Cl2+2HI=2HCl+I2反应机理的理论研究

分别在MP2/3-21G**、CCSD(T)/3-21G**//MP2/3-21G**和B3LYP/3-21G**3种水平上, 计算研究了气相反应Cl₂+2HI=2HCl+I₂的机理, 求得一系列四中心和三中心的过渡态. 通过比较六种反应通道的活化能大小, 得到了相同的结论：双分子基元反应Cl₂+HIHCl+ICl和ICl+HII₂+HCl的最小活化能小于Cl₂、HI和ICl的解离能, 从理论上证明了反应Cl₂+2HI=2HCl+I₂将优先以分子与分子作用形式分两步完成. 用内禀反应坐标(IRC)验证了MP2/3-21G**方法计算得到的过渡态.