Internal Energy State Distribution of Product CaBr in the Collision Reactions Ca+C2H5Br和Ca+nC3H7Br

The internal energy distributions of product CaBr in the collision reactions Ca+C2H5Br and Ca+nC3H7Br are studied by using the quasiclassical trajectory method. The average vibrational, rotational and translational energies and total available energies of the product CaBr molecules are calculated. The results indicate that when the collision energy is equal to 7.54 kJ/mol the energy of product CaBr is mainly the vibrational energy. As the reactant collision energy increases, the average translational and rotational energies of the product CaBr increase, the average vibrational energy decreases slightly, and the most probable vibrational state shifts to lower vibrational energy levels. The internal states of reagents have little influence on the internal energy distribution of the product. The bigger the radical group is, the higher ratio of the vibrational energy to the available energy of the product is. There exist two competitive reaction paths for the collision reactions Ca+C2H5Br and Ca+nC3H7Br, the migratory encounter and direct reaction paths. The former produces high vibrational excited state product CaBr and the latter causes C-Br bond to break. When the collision energy increases, the reactions tend to the latter path.     

Rate constant for the reaction C2H5 + HBr → C2H6 + Br

RRKM theory has been employed to analyze the kinetics of the title reaction, in particular, the once-controversial negative activation energy. Stationary points along the reaction coordinate were characterized with coupled cluster theory combined with basis set extrapolation to the complete basis set limit. A shallow minimum, bound by 9.7 kJ?mol(-1) relative to C(2)H(5) + HBr, was located, with a very small energy barrier to dissociation to Br + C(2)H(6). The transition state is tight compared to the adduct. The influence of vibrational anharmonicity on the kinetics and thermochemistry of the title reaction were explored quantitatively. With adjustment of the adduct binding energy by ～4 kJ?mol(-1), the computed rate constants may be brought into agreement with most experimental data in the literature, including new room-temperature results described here. There are indications that at temperatures above those studied experimentally, the activation energy may switch from negative to positive.     

单次碰撞条件下，反应Ba+C2H5Br、n-C3H7Br、1,2-C2H4Br2、1,3-C3H6Br2的动力学研究

Under single-collision beam-gas scattering conditions the reactions Ba+ C_2H, Br、n-C_3H_7Br、1, 2-C_2H_4Br_2、1,3-C_3H_6Br_2 have been studied using laser induced fluore-scence to detect the BaBr X~2∑~+ product. The vibrational distributions, the fractions of the available energy going into vibrational and rotational energy of the BaBr products have been calculated by means. of computer simulation. It has been found that the average vibrationel energies of the BaBr products can be described as a linear function of the mass factors for the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br、1,3-C_3H_6Br, and that the potential energy surfaces for these reactions are similar. For the reactions Ba+CH_3Br、C_2H_5Br、n-C_3H_7Br, the vibrational increae, but for the reactions Ba+CH_2Br_2、1,2-C_2H_4Br_2、1,3-C_3H_6Br_2, the vibrational excitations of the BaBr products decrease greatly when the number of the carbons increase.     

Two-configuration potential energy surface for the Ca + HF → CaF + H reaction

The three-dimensional potential energy surface for the reaction of Ca and HF has been obtained from a two-configuration direct minimization method using an extended GTO basis set. Features of the surface were examined by fitting calculated values using cubic splines. The height of the barrier to reaction was found to be quite insensitive to the direction of the impinging Ca atom for a wide range of angles of approach. The transition state occurs in the exit channel at an angle of approach of 77°, 33.6 kcal/mole (or 14.8 kcal/mole if the correlation energy error is considered) above the reactants asymptote. A further analysis of the basis set superposition error and the correlation energy error is presented, these results modify the dynamical properties of the system and give a criterion to test the validity of the previously reported two-configuration PES for BeFH and MgFH systems.     

State-to-State Quantum Dynamical Study of H+Br2→HBr+Br Reaction

The time-dependent wave packet method has been employed to calculate the state-to-state integral cross sections and differential cross sections (DCSs) for three initial states of the title reaction on the recently constructed neural network potential energy surface. It is found that the product HBr(\begin{document}$ v' $\end{document} = 2, 3, 4) states have the dominated population in the entire energy region considered here, indicating an inverted HBr vibrational state distribution. More than half of the available energy ends up as product internal motion, and most of which goes into the vibrational motion. Our calculations show that initial rotational excitation of Br\begin{document}$ _2 $\end{document} has little effect on the product ro-vibrational state distributions and DCSs of the reaction. While the initial vibrational excitation has some influences. The initial vibrational excitation to \begin{document}$ v_0 $\end{document} = 5 obviously enhance the product vibrational excitation in the low energy region. The DCSs for collision energy up to 0.5 eV at the ground and rotationally excited state are peaked in the backward direction, but the width of the angular distribution increases considerably with the increase of collision energy. For the vibrationally excited state, the DCSs are rather complicated with some strong forward scattering peaks for highly vibrationally excited products.     

KrF激光诱导BrC2F4Br+C2H4反应

激光诱导化学合成是一有兴趣的课题。不久前已报导了红外激光诱导调聚反应的结果。由于红外激光的加热特性,在许多情况下导致选择性与量子产率的矛盾。因紫外光反应的低温特性,有可能获得较高的选择性。但普通光源是宽带光源,对一个以平方断链为主的链反应,过强的吸收不利于链长的提高,而弱吸收又使反应速度太慢。为此,激光光源是满足最佳吸收的合宜光源。在使用了昂贵的激光光源后,经济上的合理性主要取决于链长     

State-selected ion-molecule reactions: H+2(ν) + He → HeH+ + H and He + H+ + H

Total cross sections for production of HeH⁺ and H⁺ in the reaction of state-selected H⁺₂ (v = 0 to 6) with He at 3.1 eV c.m. collision energy are measured by means of the threshold-photoelectron/photoion coincidence method, using pulsed synchrotron radiation. Both reaction cross sections are observed to rise with vibrational energy. The H⁺/HeH⁺ branching ratio, which is determined directly, remains approximately constant at about 0.3 for v ⩽ 3 and rises gradually for higher levels to reach the value 1.3 for v = 6. For v ⩽ 3 both reactions involve hard-type collisions and result in large-angle scattering. In contrast, at higher v levels, the HeH⁺ becomes essentially forward scattered with respect to the incident He direction, but with a velocity greater than that expected from the spectator stripping model. The H⁺ products are backward scattered with respect to the incident H⁺₂ for v ⩽ 1 and receed faster from the He atom than the H products. This observation directly leads to the conclusion that collision-induced dissociation from v = 0 and 1 involves transitions to the first excited potential-energy surface.     

New ab initio potential energy surface for BrH2 and rate constants for the H + HBr → H2 + Br abstraction reaction

A global potential energy surface (PES) for the electronic ground state of the BrH(2) system was constructed based on the multireference configuration interaction (MRCI) method including the Davidson's correction using a large basis set. In addition, the spin-orbit correction were computed using the Breit-Pauli Hamiltonian and the unperturbed MRCI wavefunctions in the Br + H(2) channel and the transition state region. Adding the correction to the ground state potential, the lowest spin-orbit correlated adiabatic potential was obtained. The characters of the new potential are discussed. Accurate initial state specified rate constants for the H + HBr → H(2) + Br abstraction reaction were calculated using a time-dependent wave packet method. The predicted rate constants were found to be in excellent agreement with the available experimental values and much better than those obtained from a previous PES.     

氢抽提反应CHBr2+HBr→CH2Br2+Br的直接动力学研究

采用直接动力学方法,对CHBr2+HBr→CH2Br2+Br反应通道进行了理论研究,在B3LYP/6-311+G(d,p)水平下获得了优化几何构型、频率以及最小能量路径,更精确的单点能在B3LYP/6-311++G(3df,2pd)水平下完成.利用正则变分过渡态理论,结合小曲率隧道效应校正方法计算了反应通道在220 K～2 000 K温度范围内的速率常数.在整个反应区间,隧道效应对反应的影响比较大;变分效应在低温时有一定的影响,在高温区间的影响很小可以忽略.计算得到的速率常数和已有实验值很好地吻合.     

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.     

Kinetic study of the reactions Br + IBr→I + Br2 and I + Br2→Br + IBr

The kinetics of the title reactions have been studied using the discharge-flow mass spectrometic method at 296 K and 1 torr of helium. The rate constant obtained for the forward reaction Br+IBr→I+Br₂ (1), using three different experimental approaches (kinetics of Br consumption in excess of IBr, IBr consumption in excess of Br, and I formation), is: k₁=(2.7±0.4)×10⁻¹¹ cm³ molecule⁻¹s⁻¹. The rate constant of the reverse reaction: I+Br₂→Br+IBr (−1) has been obtained from the Br₂ consumption rate (with an excess of I atoms) and the IBr formation rate: k₋₁=(1.65±0.2)×10⁻¹³ cm³molecule⁻¹s⁻¹. The equilibrium constant for the reactions (1,−1), resulting from these direct determinations of k₁ and k₋₁ and, also, from the measurements of the equilibrium concentrations of Br, IBr, I, and Br₂, is: K₁=k₁/k₋₁=161.2±19.7. These data have been used to determine the enthalpy of reaction (1), ΔH₂₉₈°=−(3.6±0.1) kcal mol⁻¹ and the heat of formation of the IBr molecule, ΔH_f,298°(IBr)=(9.8±0.1) kcal mol⁻¹. © 1998 John Wiley & sons, Inc. Int J Chem Kinet 30: 933–940, 1998     

Rate coefficient for the reaction: Br+Br2O→Br2+BrO

The room temperature rate coefficient for the reaction Br+Br₂O→Br₂+BrO (3) has been measured using the technique of pulse-laser photolysis with long-path transient absorption detection of the BrO reaction product. A value of k₃=(2.0±0.5)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ was determined. The photolysis products of Br₂O at 308 nm were also examined. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 571–576, 1998     

Gas phase bimolecular chemistry of isomeric C3H6Br+ cations

The gas phase chemistry of C₃H₆Br⁺ cations generated via low energy electron impact on various dibromopropanes has been studied by using Fourier transform ion cyclotron resonance mass spectrometry. Neutral substrate molecules that have been selected to probe the bimolecular reactivity of the C₃H₆Br⁺ isomers are ammonia, methylamine, trimethylamine, cis-butene, and 2, 3-dimethyl-2-butene. At least three different isomers are characterized on the basis of their different reactivity toward the various substrate molecules. It is suggested that these isomers have (a) the 2-bromo-2-propyl cation structure, (b) the propylenebromomum ion structure, and (c) the cyclic four-membered trimethylenebromonium ion structure. The 2-bromo-2-propyl cations react predominantely via proton transfer. This reaction is hampered for the propylenebromonium ions, which react mainly as electrophiles or bromanyl cation donors. Cyclic trimethylenebromoruum ions react predominantly via adduct formation, even under low pressure conditions, which implies that tturd body collisions are not the only stabilization mechanism.     

The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k₁. The reaction scheme is where k₂ ? k₁ and k_?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k₁ were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol^?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (²P_1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.     

Ab initio potential-energy surface for the reaction Ca+HCl-->CaCl+H

The potential-energy surface of the ground electronic state of CaHCl has been obtained from 6400 ab initio points calculated at the multireference configuration-interaction level and represented by a global analytical fit. The Ca+HCl-->CaCl+H reaction is endothermic by 5100 cm(-1) with a barrier of 4470 cm(-1) at bent geometry, taking the zero energy in the Ca+HCl asymptote. On both sides of this barrier are potential wells at linear geometries, a shallow one due to van der Waals interactions in the entrance channel, and a deep one attributed to the H(-)Ca(++)Cl(-) ionic configuration. The accuracy of the van der Waals well depth, approximately 200 cm(-1), was checked by means of additional calculations at the coupled-cluster singles and doubles with perturbative triples level and it was concluded that previous empirical estimates are unrealistic. Also, the electric dipole function was calculated, analytically fitted in the regions of the two wells, and used to analyze the charge shifts along the reaction path. In the insertion well, 16,800 cm(-1) deep, the electric dipole function confirmed the ionic structure of the HCaCl complex and served to estimate effective atomic charges. Finally, bound rovibrational levels were computed both in the van der Waals well and in the insertion well, and the infrared-absorption spectrum of the insertion complex was simulated in order to facilitate its detection.     

Switching between molecular switch types by module rearrangement: Ca2+-enabled, H+-driven 'Off-On-Off', H+-driven YES and PASS 0 as well as H+, Ca2+-driven AND logic operations

Several logic gates and switches can be accessed from two different combinations of a single set of fluorophore, receptor and spacer components.     

Theoretical study on the rate constants for the C2H5 + HBr --> C2H6 + Br reaction

The reaction C(2)H(5) + HBr --> C(2)H(6) + Br has been theoretically studied over the temperature range from 200 to 1400 K. The electronic structure information is calculated at the BHLYP/6-311+G(d,p) and QCISD/6-31+G(d) levels. With the aid of intrinsic reaction coordinate theory, the minimum energy paths (MEPs) are obtained at the both levels, and the energies along the MEP are further refined by performing the single-point calculations at the PMP4(SDTQ)/6-311+G(3df,2p)//BHLYP and QCISD(T)/6-311++G(2df,2pd)//QCISD levels. The calculated ICVT/SCT rate constants are in good agreement with available experimental values, and the calculate results further indicate that the C(2)H(5) + HBr reaction has negative temperature dependence at T < 850 K, but clearly shows positive temperature dependence at T > 850 K. The current work predicts that the kinetic isotope effect for the title reaction is inverse in the temperature range from 200 to 482 K, i.e., k(HBr)/k(DBr) < 1.     

Quantum scattering calculation for reaction Br + H2 on two potential energy surfaces

Three‐dimensional time‐dependent quantum wave packet calculations have been carried out for Br + H₂ on a new global ab initio and a semi‐empirical extended London–Eyring–Polanyi–Sato potential energy surface. It is shown that on the ab initio surface, the threshold energy is much lower, and the reaction probabilities, cross sections, and rate constants are much larger. The effects of the initial rovibrational excitation have also been studied. Comparison of rate constants with experimental measurement implies that the ab initio surface is more suitable for quantum dynamic calculation. The possible reasons and mechanism for the dynamical difference on the two PES are analyzed and discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007