A2B模型分子红典轨迹的辛算法计算

采和辛算法计算了Ａ２Ｂ模型分子的经典轨迹并与传统Ｒｕｎｇｅ－Ｋｕｔｔａ（Ｒ－Ｋ）算法进行了比较。结果表明，在反应动力学研究所应考虑的时间范围内，辛算法的结果与理论分析一致，Ｒ－Ｋ法的结果则面目全非。因此，用辛算法替代传统数值方法有可能克服目前经典轨变计算存在的困难，从根本上改进微观反应动力学研究的经典轨迹方法。     

铁(Ⅲ)-高碘酸钾-过氧化氢-变色酸2R催化动力学光度法测定痕量铁的研究

研究了测定铁的一种新指示反应，在稀硫酸介质中，痕量铁（Ⅲ）对高碘酸钾与过氧化氢协同氧化变色酸２Ｒ的褪色反应具有强烈催化作用，其反应的动力学条件，表观活化能Ｅ′＝１８９．８１ｋＪ／ｍｏｌ，表观反应速率常数Ｋ＝５．６７×１０－４／ｓ，半衰期ｔ１／２＝２０．３７ｍｉｎ。反应温度为９０℃，试验表明ｌｇＡ０／Ａ与Ｆｅ（Ⅲ）的浓度在３０～１００ｎｇ／２５ｍＬ范围内符合Ｂｅｒ定律，建立了催化动力学光度法测定痕量铁的新方法。方法的检测限为１．２５×１０－９ｇ／Ｌ，加入回收率在９７．０％～１０２％，应用于测定西洋参口服液、美国花旗参茶和天然矿泉水中铁的含量结果满意。     

异丙基膦酸单(1-已基-4-乙基)辛酯的某些基本常数的测定

用两相滴定法测定异丙基膦酸单（１－己基－４－乙基）辛酯（ＰＴ－２，ＨＬ）在水中的溶解度Ｓ，在水中的解离常数Ｋ在水－正庚烷中的分配常数Ｋｄ及二聚常数Ｋ２，利用ＳＯＬＷＲ计算程序，简单快速地处理两相滴定数据，得到结果为：Ｓ＝３．６８ × １０－５ｍｏｌ／Ｌ，ｐＫａ＝５．４９，ｌｏｇ Ｋ２＝４． ６７，ＩｏｇＫｄ＝ ２． ６７（２５±０． ５℃）．     

2—羟基苄叉罗丹宁合成及用作钯的光度试剂

本文报道新试剂２－羟基苄叉罗丹宁的合成，用分光光度法测定２－ＨＢＲ的离解常数，ＰＫａ１＝９．４３，ｐＫａ２＝１１．７１。研究了２－ＨＢＲ与钯的配位反应。     

O（＇D）＋N_2O反应动力学的理论研究

本文使用基态Ｎ＿２Ｏ＿２的多体项展式势能函数，并采用准经典轨迹方法研究了（１）Ｏ（＇Ｄ）＋Ｎ＿２Ｏ→２ＮＯ；（２）两个反应。求得了相对平动能为０．１～１．３ｅｖ时的反应截面及产物的角度分布，振动分布及总资用能的分配。计算结果表明，反应（１）和（２）都是无阈能的前向散射的碰撞反应。进一步求得３００Ｋ时宏观速度常数分别为１．２２×１０－（１０）和０．６８×１０￣（－１０）ｃｍ￣３．ｍｏｌｅｃｕｌｅ－１．Ｓｅｃ－１，与实测值０．７２×１０￣（１０）和０．４４×１０￣（－１０）ｃｍ￣３．ｍｏｌｅｃｕｌｅ－１．Ｓｅｃ－１相一致。     

meso—四（4—磺基苯基）卟啉（TPPS）在水及胶束体系中的二聚行为研究

研究了ｍｅｓｏ－四（４－磺基苯基）卟啉在胶束，ＫＣｌ水溶液中的电子吸收光谱变化，计算了ＴＰＰＳ的二聚常数ＫＤ，用分光光度法研究了ＴＰＰＳ在ＫＣｌ水溶液中的二聚反应动力学，提出了与实验结果相吻合的二聚机理。根据温度对二聚平衡的影响。     

Pd（Ⅱ）与α－氨基肟配体PnAO配位反应的动力学研究

本文用紫外可见分光光度法研究了Ｐｄ（Ⅱ）与ＰｎＡＯ生成配合物的反应动力学，测得了几个温度下的反应表观速率常数，提出了一个由螯合作用促进的多步反应机理，计算求得了速率控制步骤的反应速率常数和该步的活化参数，△Ｈ≠＝５７．５７ｋＪ·ｍｏｌ－１，△Ｓ≠＝－３４．２４Ｊ·ｍｏｌ－１·Ｋ－１。讨论了介质酸度和离子强度对反应速率的影响．     

铁（Ⅲ）—高碘酸钾—过氧化氢—变色酸2R催化动力学光度法测定痕量铁…

研究了测定铁的一种新指示反应，在稀硫酸介质中，痕量铁（Ⅲ）对高碘酸钾与过氧化氢协同氧化变色酸２Ｒ的褪色反应具有强烈催化作用，其反应动力学条件，表观活化能Ｅ′＝１８９．８１ｋＪ／ｍｏｌ表观反应速率常数Ｋ＝５．６７×１０＾－４／ｓ半衰期ｔ１／２＝２０．３７ｍｉｎ，反应温度为９０℃，试验表明１ｇＡ０／Ａ与Ｆｅ（Ⅲ）的浓度在３０～１００ｎｇ／２５ｍＬ，范围内符合Ｂｅｅｒ定律，建立了催化动力学光度法测定痕量     

在N—甲基吡咯烷酮中聚苯硫醚合成的宏观动力学

研究了无水硫化钠与对二氯苯（以Ｎ－甲基吡咯烷酮为溶剂）合成聚苯硫醚反应的宏观动力学，该反应是一个小分子缩合串联自缩聚的过程，通过测定不同反应聚合体系中氯化钠的徨成率和硫化内的转化率，建立了该反应的宏观动力学方程：１／（１－ＰＮａＣｌ＋ＰＮａ２ｓ）＝Ｃ０Ｋｔ＋１；并计算得到２２０、２５０℃的表观反应速率为４．５×１０＾－４和３．０×１０＾－３ｋｇ／（ｍｏｌ．ｓ），表观活化能为１３４ｋＪ／ｍｏｌ。     

Pd(Ⅱ)与α－氨基肟配体PnAO配位反应的动力学研究

本文用紫外可见分光光度法研究了Ｐｄ（Ⅱ）与ＰｎＡＯ生成配合物的反应动力学，测得了几个温度下的反应表观速率常数，提出了一个由螯合作用促进的多步反应机理，计算求得了速率控制步骤的反应速率常数和该步的活化参数，△Ｈ＾≠＝５７．５７ｋＪ．ｍｏｌ＾－１．Ｋ＾－１。讨论了介质酸度和离子强度对反应速率的影响。     

Reaction rate calculation with time-dependent invariant manifolds

The identification of trajectories that contribute to the reaction rate is the crucial dynamical ingredient in any classical chemical reactivity calculation. This problem often requires a full scale numerical simulation of the dynamics, in particular if the reactive system is exposed to the influence of a heat bath. As an efficient alternative, we propose here to compute invariant surfaces in the phase space of the reactive system that separate reactive from nonreactive trajectories. The location of these invariant manifolds depends both on time and on the realization of the driving force exerted by the bath. These manifolds allow the identification of reactive trajectories simply from their initial conditions, without the need of any further simulation. In this paper, we show how these invariant manifolds can be calculated, and used in a formally exact reaction rate calculation based on perturbation theory for any multidimensional potential coupled to a noisy environment.     

Evolution of conformational changes in the dynamics of small biological molecules: a hybrid MD/RRK approach

The dynamics of long timescale evolution of conformational changes in small biological molecules is described by a hybrid molecular dynamics/RRK algorithm. The approach employs classical trajectories for transitions between adjacent structures separated by a low barrier, and the classical statistical RRK approximation when the barrier involved is high. In determining the long-time dynamics from an initial structure to a final structure of interest, an algorithm is introduced for determining the most efficient pathways (sequence of the intermediate conformers). This method uses the Dijkstra algorithm for finding optimal paths on networks. Three applications of the method using an AMBER force field are presented: a detailed study of conformational transitions in a blocked valine dipeptide; a multiple reaction path study of the blocked valine tripeptide; and the evolution in time from the beta hairpin to alpha helix structure of a blocked alanine hexapeptide. Advantages and limitations of the method are discussed in light of the results.     

Nonadiabatic excited-state molecular dynamics: numerical tests of convergence and parameters

Nonadiabatic molecular dynamics simulations, involving multiple Born-Oppenheimer potential energy surfaces, often require a large number of independent trajectories in order to achieve the desired convergence of the results, and simulation relies on different parameters that should be tested and compared. In addition to influencing the speed of the simulation, the chosen parameters combined with the frequently reduced number of trajectories can sometimes lead to unanticipated changes in the accuracy of the simulated dynamics. We have previously developed a nonadiabatic excited state molecular dynamics methodology employing Tully's fewest switches surface hopping algorithm. In this study, we seek to investigate the impact of the number of trajectories and the various parameters on the simulation of the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene) within our developed framework. Various user-defined parameters are analyzed: classical and quantum integration time steps, the value of the friction coefficient for Langevin dynamics, and the initial seed used for stochastic thermostat and hopping algorithms. Common approximations such as reduced number of nonadiabatic coupling terms and the classical path approximation are also investigated. Our analysis shows that, at least for the considered molecular system, a minimum of ~400 independent trajectories should be calculated in order to achieve statistical averaging necessary for convergence of the calculated relaxation timescales.     

Effect of molecular vibrations on the MD/QC‐simulated absorption spectra

Effect of molecular vibrations on the absorption spectra simulated via a sequential approach combining molecular dynamics (MD) with quantum‐chemical calculations has been investigated. Simulated spectra have been obtained from the time‐dependent density functional theory results averaged over series of molecular geometries retrieved from Born–Oppenheimer MD trajectories. Distributions of bond lengths have been analyzed and related to the features of calculated spectra. For NVE simulations of small systems, absorption spectra exhibit bimodal bandshape as a result of classical treatment of vibrations. For NVE trajectories of larger systems or simulations in the NVT ensemble calculated absorption bands are symmetric, however, they may not agree with the results of Franck–Condon analysis. These results are practical manifestations of effects predicted theoretically from general principles. Consequences for the modeling of absorption spectra have been discussed. © 2013 Wiley Periodicals, Inc.     

Independent trajectory implementation of the semiclassical Liouville method: application to multidimensional reaction dynamics

We describe an independent trajectory implementation of semiclassical Liouville method for simulating quantum processes using classical trajectories. In this approach, a single ensemble of trajectories describes all semiclassical density matrix elements of a coupled electronic state problem, with the ensemble evolving classically under a single reference Hamiltonian chosen on the basis of physical grounds. In this paper, we introduce an additional uncoupled trajectory approximation, allowing the members of the ensemble to evolve independently of one another and eliminating the major computational costs of our previous coupled trajectory implementation. The accuracy of the method is demonstrated for model one-dimensional problems. In addition, the approach is applied to the chemical reaction dynamics of a collinear triatomic system, yielding excellent agreement with exact calculations. This method allows molecular dynamics involving coupled electronic surfaces to be modeled with essentially the same effort as classical molecular dynamics and ensemble averaging.     

Representing and selecting vibrational angular momentum states for quasiclassical trajectory chemical dynamics simulations

Linear molecules with degenerate bending modes have states, which may be represented by the quantum numbers N and L. The former gives the total energy for these modes and the latter identifies their vibrational angular momentum jz. In this work, the classical mechanical analog of the N,L-quantum states is reviewed, and an algorithm is presented for selecting initial conditions for these states in quasiclassical trajectory chemical dynamics simulations. The algorithm is illustrated by choosing initial conditions for the N = 3 and L = 3 and 1 states of CO2. Applications of this algorithm are considered for initial conditions without and with zero-point energy (zpe) included in the vibrational angular momentum states and the C-O stretching modes. The O-atom motions in the x,y-plane are determined for these states from classical trajectories in Cartesian coordinates and are compared with the motion predicted by the normal-mode model. They are only in agreement for the N = L = 3 state without vibrational angular momentum zpe. For the remaining states, the Cartesian O-atom motions are considerably different from the elliptical motion predicted by the normal-mode model. This arises from bend-stretch coupling, including centrifugal distortion, in the Cartesian trajectories, which results in tubular instead of elliptical motion. Including zpe in the C-O stretch modes introduces considerable complexity into the O-atom motions for the vibrational angular momentum states. The short-time O-atom motions for these trajectories are highly irregular and do not appear to have any identifiable characteristics. However, the O-atom motions for trajectories integrated for substantially longer period of times acquire unique properties. With C-O stretch zpe included, the long-time O-atom motion becomes tubular for trajectories integrated to approximately 14 ps for the L = 3 states and to approximately 44 ps for the L = 1 states.     

Computation of quasiclassical trajectories by symplectic algorithm for the N(4S) + O2(X ^{3}\Sigma_{\rm g}^{-})\rightarrow NO(X2Π) + O(3P) reaction system

Computation of quasiclassical trajectories for the N(⁴S) + O₂(X $^{3}\Sigma_{\rm g}^{-})\!\rightarrow\!$  NO(X²Π)  + O(³P) atmospheric reaction system, based on a new ground potential energy surface reported by R.Sayós et al., has been performed in this work by means of both the fourth-order explicit symplectic algorithm (S4) and the fourth-order Runge–Kutta scheme (RK4), and then computed results of two schemes are compared. It is shown that RK4 cannot preserve energy conservation and symplectic structure of the reaction system, which results in the bad veracity of the trajectory calculation. RK4 cannot rightly reflect both the colliding mode and the reaction mode of the trajectories. Moreover, the amplitudes of vibration of the reactant molecule and the product molecule become gradually small with the time increasing, and their rotation–vibrational levels in fact vary during the integration. For these reasons, RK4 cannot assure the accuracy of the quasiclassical trajectory (QCT) study of the atmospheric reaction. However, S4 maintains these characteristics and can actually describe the circumstance of the reaction system. S4 is better than RK4 is prospective in the QCT study of the chemical reaction.     

Two‐dimensional reactive scattering with transmitted quantum trajectories

A simple and easy‐to‐implement method is presented for the study of time‐dependent reaction dynamics by propagating an ensemble of transmitted quantum trajectories. During the trajectory evolution, reflected trajectories are gradually removed and all the remaining trajectories represent the transmitted subensemble. The removal process of reflected trajectories avoids numerical instabilities arising from node formation in the reactant region, and allows stable long‐time propagation of transmitted trajectories. This method is applied to a two‐dimensional model chemical reaction. Excellent computational results are obtained for the time‐dependent reaction probabilities evaluated by the time integration of the probability flux. © 2014 Wiley Periodicals, Inc.     

Transition state dynamics of Ar(n).(IHI) (n = 0-20)

Classical trajectory simulations of the dynamics of Ar(n).(IHI) with n = 0-20 are performed to investigate the effects of solvation on the transition state dynamics of the I + HI reaction. Initial conditions for the classical trajectories are sampled from the quantum ground-state phase space distribution for Ar(n).(IHI)-, given by the Wigner distribution function. Neumark and co-workers recently reported a shift of the Ar(n).(IHI)- photoelectron spectra to lower electron kinetic energies when the number of argon atoms was increased from 0 to 15. Analogous shifts are found in the present calculations, and excellent agreement between the experimental and calculated shifts is found. Longer lifetimes of the IHI complex and increasing energy transfer between the hydrogen atom and the argon and iodine atoms are also observed as the number of argon atoms is increased.