Quantum wave packet calculation of reaction probabilities,cross sections,and rate constants for H+ + LiH → Li + H reaction

The H⁺ + LiH → Li + H reactive scattering has been studied using a quantum real wave packet method. The state‐to‐state and state‐to‐all reaction probabilities for the entitled collision have been calculated at zero total angular momentum. The probabilities for J > 0 are estimated from the J = 0 results by using J‐shifting approximation based on the Capture model. The integral cross sections and thermal rate constants are then calculated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Quantum wave packet calculation of reaction probabilities,cross sections,and rate constants for the C(1D) + HD reaction

The time‐dependent real wave packet method has been used to study the C(¹D) + HD reaction. The state‐to‐state and state‐to‐all reactive scattering probabilities for a broad range of energies are calculated at zero total angular momentum. The probabilities for J > 0 are estimated from accurately computed J = 0 probabilities by using the J‐shifting approximation. The integral cross sections for a large energy range, and thermal rate constants are calculated. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Time‐dependent quantum study of H(2S) + FO(2Π) → OH(2Π) + F(2P) reaction on the 13A′ and 13A″ states

The dynamics of the H(²S) + FO(²Π) → OH(²Π) + F(²P) reaction on the adiabatic potential energy surface of the 1³A′ and 1³A″ states is investigated. The initial state selected reaction probabilities for total angular momentum J = 0 have been calculated by using the quantum mechanical real wave packet method. The integral cross sections and initial state selected reaction rate constants have been obtained from the corresponding J = 0 reaction probabilities by means of the simple J‐Shifting technique. The initial state‐selected reaction probabilities and reaction cross section do not manifest any sharp oscillations and the initial state selected reaction rate constants are sensitive to the temperature. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

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     

Energy resonance and inverse population of the product vibrational states for the reaction F + H2(v = 0) → HF(v′) + H,LCAC‐SW theoretical quantum scattering study

LCAC‐SW (linear combination of arrangement channel‐scattering wavefunction) method was used to calculate collinear state‐to‐state reaction probabilities for the reaction F + H₂(v = 0) → HF(v′) + H on the 6SEC potential energy surface. The results show that reaction probabilities P₀₂ and P₀₃ [i. e., v′ = 2,3 for reaction F + H₂ (v = 0) + HF(v′) + H] are primary, the population of product vibrational states is inverse and the reaction probabilities are oscillatory with collision energies, i.e., there is energy resonance in this reaction, which agrees with a new experiment.     

Direct calculation of resonant states in reactive scattering. Application to linear triatomic systems

A direct method for calculating resonant states in reactive scattering is suggested, permitting us to obtain the characteristics of multichannel resonances (partial width amplitudes). The method is based on the construction of a Laurent expansion of the scattering matrix S(? ?iΓ/2) in the complex plane. The position of the poles of the S matrix are derived by solving the dynamical problem with complex energy values. The residue at the pole gives all the information concerning the partial widths. The method is applied to a linear triatomic reactive scattering problem. The properties of the resonant states in the H + H₂ system are calculated as an example. Two broad resonances are found which have not been reported in previous calculations. The interference of overlapping resonances is shown to have a profound effect on the energy dependence of the transition probabilities.     

Collinear quantum mechanical calculations of the He + H+2 proton transfer reactions

Exact quantum mechanical results for collinear He + H⁺₂ → H + HeH⁺ reactive collisions are presented for the (total) energy range of 0.93 cV to 1.4 eV. The H⁺₂ initial vibrational states include ν = 0 through ν = 5. The diatomics-in-molecules semi-empirical surface of Kuntz is used in the computations. Except for a short range of energies, the calculated reaction probabilities of H⁺₂ (ν = 0) are larger than those of excited H⁺₂.     

Quantum scattering LCAC-SW theory studies on reaction probabilities of three-dimensional H + H2 (v, j) → H2 (v′, j′) + H reaction

Upon the Liu, Siegbahn, Truhlar, Horowitz (LSTH) potential energy surface, the reaction probabilities of the three-dimensional (3-D) state-to-state H + H₂ (v, j) →H ₂(v′, j′) + H reaction are calculated with the linear combination of arrangement channels-scattering wavefunction (LCAC-SW) method. In the calculation, the vibration function of H₂ and the radial propagating wave functions are expanded by the real Gauss functions. The calculated threshold energy and the resonating structure are consistent with the results of the accurate quantum scattering calculations, which shows the accuration, simplicity and practicability of the LCAC-SW method. Project supported by the National Natural Science Fondation of China and the Doctoral Foundation of the State Education Commission of China.     

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.     

Theoretical study of the reaction Ne + H+2 → NEH+ + H in the 2A′ ground state

A three-dimensional potential energy surface for the ²A′ ground state of the system (Ne? H₂)⁺ (²Σ⁺ in collinear geometry) has been calculated at SCF and CEPA levels. This surface describes the abstraction reaction which is endoergic by 0.57 eV (ΔH⁰₀) and has been studied recently by different experimental groups at low collision energies. Our CEPA calculations yield an endoergicity of 0.55 eV (ΔH⁰₀). The ²A′ surface has a minimum at collinear geometry with R_Ne—H = 2.29 a₀ and R_{H? H} = 2.08 a₀ and a well depth of 0.49 eV relative to Ne + H⁺₂. The effects of electron correlation on the shape of the surface and on the well depth are discussed. An analytic fit of the collinear part of the surface has been constructed based on Simon's proposal of using polynomials in the coordinates (R? R_e)/R instead of (R? R_e). The fitted potential is used for quantum mechanical scattering calculations with the finite element method (FEM ). Preliminary results for reaction probabilities for H⁺₂ in different vibrationally excited states are given and compared to the experimental results.     

Study of the [Cr(H2O)5NO]2+ Complex via Density Functional Theory

On the basis of density functional theory, the spin ground state of chromium‐nitrosyl complex [Cr(H₂O)₅NO]²⁺ (S = 1/2) is studied via B3LYP hybrid method. Its vibrational frequencies, atomic charges, and spin densities are analyzed. The excitation energies are evaluated using the CIS method. Our calculated N‐O stretching frequency and excitation energies are in good agreement with the IR and UV‐vis data. The related Cr^I(H₂O)₆⁺, Cr^II(H₂O)₆²⁺, and Cr^III(H₂O)₆³⁺ complexes are employed as the reference compounds to determine the characteristics of the central Cr. Results indicate that the effective Cr oxidation state is close to Cr(I).     

Selective J‐resolved‐HMQC‐1 and ‐2, new methods for measuring proton–proton coupling constants in strongly coupled spin systems

Efficient pulse sequences for measuring ¹H–¹H coupling constants (J_HH) in strongly coupled spin systems, named selective J‐resolved‐HMQC‐1 and ‐2, have been developed. In the strongly coupled spin systems such as ‐CH₂‐CH_A(OH)‐CH_B(OH)‐CH₂‐, measurements of ³J_HAHB are generally difficult owing to the complicated splitting caused by the adjacent CH₂ protons. For easier and accurate measurements of ³J_HAHB in such a spin system, a selective excitation pulse is incorporated into the J‐resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, H_A and H_B which are excited by a selective pulse, are observed as J‐resolved HMQC signals. The cross peaks of H_A and H_B appear as doublets owing to ³J_HAHB along the F₁ dimension in the selective J‐resolved HMQC‐1 and ‐2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin. Copyright © 2011 John Wiley & Sons, Ltd.     

Photoinduced Charge‐Transfer Interactions on a Graphene/Block Copolymer Electrostatically Bound to Tetracationic Porphyrin in Aqueous Media

Stable dispersions of exfoliated graphene in aqueous media with the aid of the amphiphilic block copolymer poly(isoprene‐b‐acrylic acid) (PI‐b‐PAA), in the form of its anion, were used to electrostatically bind cationic 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridinio)porphine tetra(p‐toluenesulfonate) (H₂P⁴⁺). A new graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble was formed and examined by dynamic light scattering, UV/Vis and fluorescence emission spectroscopy. The efficient fluorescence quenching of H₂P⁴⁺ in the graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble was probed by using steady‐state and time‐resolved photoluminescence, suggesting that electron/energy‐transfer phenomena occur within the nanoensemble. Blank experiments validated the concept of electrostatic interactions that govern the formation of graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble, which signified the importance of graphene as an electron acceptor toward the preparation of some new donor–acceptor systems. Finally, kinetic analysis of the lifetime profiles of the fluorescence emission gave information regarding the quenching rate constant and quantum yield of the singlet excited state of H₂P⁴⁺ in the graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble.     

Electronic nonadiabatic transitions in the reactive (Ar+ + H2, Ar + H+2, ArH+ + H) system. Numerical results for the collinear configuration

In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar⁺ + H₂(v_i = 0) → ArH⁺(v_f) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between v_i = 0 of the Ar⁺ + H₂ system and v_i = 2 of the Ar + H⁺₂ system. The threshold for the reaction is found to be 0.06 eV.     

Direct quantum mechanical calculation of the F + H2 → HF + H thermal rate constant

Accurate full-dimensional quantum mechanical thermal rate constant values have been calculated for the F+H₂→HF+H reaction on the Stark–Werner ab initio potential energy surface. These calculations are based on a flux correlation functions and employ a rigorous statistical sampling scheme to account for the overall rotation and the MCTDH scheme for the wave packet propagation. Our results shed some light on discrepancies on the thermal rate found for previous flux correlation based calculations with respect to accurate reactive scattering results. The resonance pattern of the all-J cumulative reaction probability is analyzed in terms of the partial wave contributions.     

BASHD‐J‐resolved‐HMBC,an efficient method for measuring proton–proton and heteronuclear long‐range coupling constants

Natural products often possess various spin systems consisting of a methine group directly bonded to a methyl group (e.g. –CH_a–CH_b(CH₃)–CH_c–). The methine proton H_b splits into a broadened multiplet by coupling with several vicinal protons, rendering analysis difficult of ⁿJ_C–H with respect to H_b in the J‐resolved HMBC‐1. In purpose of the reliable and easy measurements of ⁿJ_C–H and ⁿJ_H–H in the aforesaid spin system, we have developed a new technique, named BASHD‐J‐resolved‐HMBC. This method incorporates band selective homo decoupled pulse and J‐scaling pulse into HMBC. In this method, high resolution cross peaks can be observed along the F₁ axis by J‐scaling pulse, and band selective homo decoupled pulse simplified multiplet signals. Determinations of ⁿJ_C–H and ⁿJ_H–H of multiplet signals can easily be performed using the proposed pulse sequence. Copyright © 2013 John Wiley & Sons, Ltd.     

How Frustrated Lewis Acid/Base Systems Pass through Transition‐State Regions: H2 Cleavage by [tBu3P/B(C6F5)3]

We investigate the transition‐state (TS) region of the potential energy surface (PES) of the reaction tBu₃P+H₂+B(C₆F₅)₃→tBu₃P‐H⁽⁺⁾+^(?)H?B(C₆F₅)₃ and the dynamics of the TS passage at room temperature. Owing to the conformational inertia of the phosphane???borane pocket involving heavy tBu₃P and B(C₆F₅)₃ species and features of the PES E(P???H, B???H | B???P) as a function of P???H, B???H, and B???P distances, a typical reactive scenario for this reaction is a trajectory that is trapped in the TS region for a period of time (about 350 fs on average across all calculated trajectories) in a quasi‐bound state (scattering resonance). The relationship between the timescale of the TS passage and the effective conformational inertia of the phosphane???borane pocket leads to a prediction that isotopically heavier Lewis base/Lewis acid pairs and normal counterparts could give measurably different reaction rates. Herein, the predicted quasi‐bound state could be verified in molecular collision experiments involving femtosecond spectroscopy.     

Computational studies on the mechanism and kinetics of Cl reaction with C2H5I

The dual‐level direct kinetics method has been used to investigate the multichannel reactions of C₂H₅I + Cl. Three hydrogen abstraction channels and one displacement process are found for the title reaction. The calculation indicates that the hydrogen abstraction from ? CH₂? group is the dominant reaction channel, and the displacement process may be negligible because of the high barrier. The rate constants for individual reaction channels are calculated by the improved canonical variational transition‐state theory with small‐curvature tunneling correction over the temperature range of 220–1500 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low‐temperature range. Agreement between the calculated and experimental data available is good. The Arrhenius expression k(T) = 2.33 × 10^?16 T^1.83 exp(?185.01/T) over a wide temperature range is obtained. Furthermore, the kinetic isotope effects for the reaction C₂H₅I + Cl are estimated so as to provide theoretical estimation for future laboratory investigation. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Cyano-bridged Ln^3＋-Cr^3＋ Binuclear Complexes [Ln（L）x（H2O）y^- Cr（CN）6]·mL·nH2O （Ln=La-Nd,x=5, y=2, m=1 or 2, n=2 or 2.5; Ln-Sm-Dy,Er, x=4, y=3, m=0, n=1.5 or 2.0; L= 2-pyrrolidinone）： Structure,Magnetism and Spin Density Map

In order to shed light upon the nature and mechanism of 4f-3d magnetic exchange interactions, a series of binuclear complexes of lanthanide（3＋） and chromium（3＋） with the general formula [Ln（L）5（H2O）2Cr（CN）6]·mL· nH2O （Ln=La （1）, Ce （2）, Pr （3）, Nd （4）; x=5, y=2, m=1 or 2, n=2 or 2.5; L=2-pyrrolidinone） and [Ln（L）4（H2O）3Cr（CN）6] ·nH2O （Ln=Sm （5）, Eu （6）, Gd （7）, Tb （8）, Dy （9）, Er （10）; x=4, y=3, m=0, n= 1.5 or 2.0; L=2-pyrrolidinone） were prepared and the X-ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln-CN-Cr unit, in which Ln^3＋ in a square antiprism environment is bridged to an octahedral coordinated Cr^3＋ ion through a cyano group. The magnetic properties of the complexes 3 and 6-10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g= 1.98, J=0.40 cm^-1, zJ＇= -0.21 cm^-1 on the basis of a binuclear spin system （Scd=7/2, Scr=3/2）, revealing an intra-molecular Gd^3＋-Cr^3＋ ferromagnetic interaction and an inter-molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory （DFT）, combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm^-1, supporting the observation of weak ferromagnetic intra-molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd^3＋ and Cr^3＋ was discussed.