Trajectory surface-hopping study of the K + O2 collision: Energy transfer in neutral and ionic products

The K + O₂ collision has been studied at low energy by three-dimensional trajectory surface-hopping calculations. The diabatic potential energy surfaces used to describe the electronic states involved in the collision have been built using an analytical semi-empirical model and have not been fitted to experimental results. The double-peak structure experimentally observed in the energy-loss spectrum for K⁺ production is confirmed; but it appears that the high-energy-loss peak is due to efficient T-V energy transfer and not to electronic excitation of the O₂^? molecular ion. The energy transfer mechanism is explained by a comparison between the vibrational period of the target and the collision time which depends upon the collision energy.     

On the origin of the dynamical threshold for collision-induced dissociation processes

Collision-induced dissociation from the ground vibration-rotation state of the reactant diatom is studied in the systems He + H₂, H + H₂, and He + H⁺₂ by quasiclassical trajectory calculations, using ab initio potential energy surfaces. The dependence of the dynamical threshold values on the shape of the potential energy surface is discussed.     

Analytical fitting of potential energy surfaces for the Hxy systems

Use of the London-Eyring-Polanyi + 3-Center + power-series (LEP -3C -PS ) analytical potential as a fit to potential energy surfaces (PES ) which are known numerically only are suggested. This analytical fit was performed for the diatomics-in-molecules + 3 Center (DIM -3C ) PES of HCl₂ and HI₂ systems. The HCl₂ analytical LEP -3C-PS potential was used for classical trajectory calculations of the Cl' + HCl → HCl' + Cl reaction. The rate constant obtained from these calculations for T = 358° K is 1.95 X 10⁹ cm³/mol sec which is close to the experimental value of 2.5 10⁹ cm³/mol sec.     

Quantum mechanical scattering calculations on a spline-fitted ab initio surface: the He + H+2 (ν = 0, 1, 2) → HeH+ + H reaction

All-channel time-dependent quantum mechanical reaction probabilities are reported for the collinear He + H⁺₂(ν = 0, 1, 2) → HeH⁺ + H reaction at a total energy of 1.2 eV on previously reported diatomics-in-molecule (DIM) and spline fitted ab initio (SAI) surfaces. These results are in agreement with the previous quasiclassical trajectory results in that there is vibrational enhancement of the reaction probability on the SAI surface but not on the DIM surface. This agreement lends support to our previously drawn conclusion that small differences in the potential-energy surface can lead to substantially different dynamic results.     

CAS SCF/CI calculations of potential energy surfaces of He3+ and He2+

Complete active space MC SCF (CAS SCF) calculations followed by second-order configuration interaction (SOCI) calculations are carried out on the potential energy surfaces (bending surface, linear surfaces) of the ²Σ_g⁺ ground state of He₃⁺. The potential minimum for the ²Σ_g⁺ state occurs at a linear geometry with HeHe bond length of 1.248 Å. The binding energy of He₃⁺ with respect to He + He⁺ + He was calculated to be 2.47 eV at the SOCI level. The energy required to dissociate He₃⁺ (²Σ_g⁺) into He₂⁺ (²Σ_u⁺) and He(¹S) is calculated to be 0.14 eV. The same level of SOCI calculations of He₂⁺ yield a D_e value of 2.36 eV.     

Laser-induced fluorescence detection of N+2(X 2Σ+g) resulting from the He(23S) + N2 and He+, He+2 + N2 reactions in a flowing afterglow

The formation processes of N⁺₂ (X ²Σ⁺_g) resulting from the He(2 ³S) + N₂ Penning ionization and the thermal energy He⁺, He⁺₂ + N₂ charge transfer reaction are studied by observing the N⁺₂ (B ²Σ⁺_u ← X ²Σ⁺_g) laser-induced fluorescence (LIF) in a flowing afterglow. In both reactions, the vibrational population) decrease monotonically with increasing vibrational quantum number from υ″ = 0 to 3, and a population inversion with a peak at υ″ = 4 is seen. In the He(2 ³S) + N₂ Penning ionization, the vibrational populations of N⁺₂ (X, υ″ = 0–2) are explained by a direct channel and the B —X radiative cascade, while those of N⁺₂ (X, υ″ = 4–6) are ascribed to the collision-induced electronic energy transfer between the A ²Π_u and X ²Σ⁺_g states. In the He⁺, He⁺₂ + N₂ reaction, the N⁺₂ (X, υ″ = 0–3) is interpreted as the B−X radiative cascade and the collisional quenching of the unidentified states produced from the He⁺ + N₂ reaction, while the collision-induced electronic energy transfer from the N⁺₂ (A) state produced through the He⁺₂ + N₂ reaction is probably important for the formation of N⁺₂ (X, υ″ = 4–6).     

Theoretical state-to-state cross sections for collisions of N2+ (X, υ) or N2+(A, υ) with Ar

State-to-state cross sections have been calculated for collisions of N⁺₂ (X, υ) or N⁺₂ (A, υ) with Ar at relative energies of 8 and 20 eV. The computations utilize potential energy surfaces computed recently by Archirel and Levy. In the calculations the translational motion is treated classically, and the time-dependent Schrödinger equation is solved exactly for the vibronic states of the system. In addition to the charge transfer and vibrational excitation and deexcitation processes, cross sections are also obtained for internal conversion between N⁺₂ (A) + Ar and N⁺₂ (X) + Ar. The results are in good agreement with the available experimental data at these energies.     

Electronic transitions in collinear H+ + D2 (ν = 0) → HD+ (ν = 0,1) + D via classical trajectories in complex time and complex phase space

A semiclassical treatment of electronic transitions in the collinear rearrangement H⁺ + D₂ (ν = 0) → HD⁺ (ν = 0,1) + D is presented. The treatment represents an extension of Stueckelberg's method for a single nuclear degree of freedom to collisions involving several nuclear degrees of freedom. The classical limit of scattering amplitudes (S-matrix elements) is calculated for the transition between the two adiabatic potential energy surfaces corresponding to the two lowest singlet states of HD⁺₂. S-matrix elements are constructed from trajectories propagating in complex time and complex phase space, which make localized transitions between the two surfaces by crossing their complex line of intersection. The action along each trajectory acquires an imaginary part, which contributes exponential damping to the corresponding amplitude for electronic transition.     

He++N2 Charge Transfer Reaction: An Ab initio Analysis

An ab initio analysis on the involved potential energy surfaces is presented for the investigation of the charge transfer mechanism for the He⁺+N₂ system. At high collision energy, as many as seven low-lying electronic states are observed to be involved in the charge transfer mechanism. Potential energy surfaces for these low-lying electronic states have been computed in the Jacobi scattering coordinates, applying multireference configuration interaction level of theory and aug-cc-pVQZ basis sets. Asymptotes for the ground and various excited states are assigned to mark the entrance (He⁺+N₂) and charge transfer channels (He+N₂⁺). Nonadiabatic coupling matrix elements and quasi-diabatic potential energy surfaces have been computed for all seven states to rationalize the available experimental data on the charge transfer processes and to facilitate dynamics studies.     

Elucidating the Doping Effect on the Electronic Structure of Thiolate‐Protected Silver Superatoms by Photoelectron Spectroscopy

Gas‐phase photoelectron spectroscopy (PES) was conducted on [XAg₂₄(SPhMe₂)₁₈]^? (X=Ag, Au) and [YAg₂₄(SPhMe₂)₁₈]^2? (Y=Pd, Pt), which have a formal superatomic core (X@Ag₁₂)⁵⁺ or (Y@Ag₁₂)⁴⁺ with icosahedral symmetry. PES results show that superatomic orbitals in the (Au@Ag₁₂)⁵⁺ core remain unshifted with respect to those in the (Ag@Ag₁₂)⁵⁺ core, whereas the orbitals in the (Y@Ag₁₂)⁴⁺ (Y = Pd, Pt) core shift up in energy by about 1.4 eV. The remarkable doping effect of a single Y atom (Y=Pd, Pt) on the electronic structure of the chemically modified (Ag@Ag₁₂)⁵⁺ superatom was reproduced by theoretical calculations on simplified model systems and was ascribed to 1) the weaker binding of valence electrons in Y@(Ag⁺)₁₂ compared to Ag⁺@(Ag⁺)₁₂ due to the reduction in formal charge of the core potential, and 2) the upward shift of the apparent vacuum level due to the presence of a repulsive Coulomb barrier between [YAg₂₄(SPhMe₂)₁₈]^? and electron.     

Nucleophilic Substitution at Phosphorus Centers (SN2@P)

We have studied the characteristics of archetypal model systems for bimolecular nucleophilic substitution at phosphorus (S_N2@P) and, for comparison, at carbon (S_N2@C) and silicon (S_N2@Si) centers. In our studies, we applied the generalized gradient approximation (GGA) of density functional theory (DFT) at the OLYP/TZ2P level. Our model systems cover nucleophilic substitution at carbon in X^?+CH₃Y (S_N2@C), at silicon in X^?+SiH₃Y (S_N2@Si), at tricoordinate phosphorus in X^?+PH₂Y (S_N2@P3), and at tetracoordinate phosphorus in X^?+POH₂Y (S_N2@P4). The main feature of going from S_N2@C to S_N2@P is the loss of the characteristic double‐well potential energy surface (PES) involving a transition state [X? CH₃? Y]^? and the occurrence of a single‐well PES with a stable transition complex, namely, [X? PH₂? Y]^? or [X? POH₂? Y]^?. The differences between S_N2@P3 and S_N2@P4 are relatively small. We explored both the symmetric and asymmetric (i.e. X, Y=Cl, OH) S_N2 reactions in our model systems, the competition between backside and frontside pathways, and the dependence of the reactions on the conformation of the reactants. Furthermore, we studied the effect, on the symmetric and asymmetric S_N2@P3 and S_N2@P4 reactions, of replacing hydrogen substituents at the phosphorus centers by chlorine and fluorine in the model systems X^?+PR₂Y and X^?+POR₂Y, with R=Cl, F. An interesting phenomenon is the occurrence of a triple‐well PES not only in the symmetric, but also in the asymmetric S_N2@P4 reactions of X^?+POCl₂? Y.     

Diatomics-in-molecules calculation of the potential energy surfaces relevant to penning ionization in the He(2 3S)H2 system

Potential energy surfaces and the autoionization width for the Penning ionization transition He(2 ³S) + H₂ → He + H⁺₂ + e^? have been calculated using the DIM method. The surfaces compare favourably with the existing ab initio calculations, and the approximation to the autoioinization width appear to be reasonable.     

Density functional theory study on the reactions of X− with CH3SY (X,Y = F,Cl, Br,I)

Gas‐phase anionic reactions X^? + CH₃SY (X, Y = F, Cl, Br, I) have been investigated at the level of B3LYP/6‐311+G (2df,p). Results show that the potential energy surface (PES) of gas‐phase reactions X^? + CH₃SY (X, Y = Cl, Br, I) has a quadruple‐well structure, indicating an addition–elimination (A–E) pathway. The fluorine behaves differently in many respects from the other halogens and the reactions F^? + CH₃SY (Y = F, Cl, Br, I) correspond to deprotonation instead of substitution. The gas‐phase reactions X^? + CH₃SF (X = Cl, Br, I), however, follow an A–E pathway other than the last two out going steps (COM2 and PR) that proceeds via a deprotonation. The polarizable continuum model (PCM) has been used to evaluate the solvent effects on the energetics of the reactions X^? + CH₃SY (X, Y = Cl, Br, I). The PES is predicted to be unimodal in the solvents of high polarity. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Distonic radical cations : Guidelines for the assessment of their stability

Ab initio molecular orbital calculations on the distonic radical cations CH₂(CH₂)_nN⁺H₃ and their conventional isomers CH₃(CH₂)_nNH₂+ (n = 0,1, 2 and 3) indicate a preference in each case for the distonic isomer. The energy difference appears to converge with increasing n towards a limit which is close to the energy difference between the component systems CH₃·H₂+CH₃^+NH₃ (representing the distonic isomer) and CH₃CH₃+CH₃NH₂+ (representing the conventional isomer). The generality of this result is assessed by using results for the component systems CH₃·Y+CH₃X⁺H and CH₃YH+CH₃X^+. (or CH₃YH^+. + CH₃X) to predict the relative energies of the distonic ions ·Y(CH₂)_nX⁺H and their conventional isomers HY(CH₂)nX^+. (X = NH₂, OH, F, PH₂, SH, Cl; Y = CH₂, NH, O) and testing the predictions through explicit calculations for systems with n = 0,1 and 2. Although the predictions based on component systems are often close to the results of direct calculations, there are substantial discrepancies in a number of cases; the reasons for such discrepancies are discussed. Caution must be exercised in applying this and related predictive schemes. For the systems examined in the present study, the conventional radical cation is predicted in most cases to lie lower in energy than its distonic isomer. It is found that the more important factors contributing to a preference for distonic over conventional radical cations are the presence in the system of a group(X) with high proton affinity and the absence of a group (X, Y or perturbed (C—C) with low ionization energy.     

离子对生成反应的LCAC-SW量子散射理论研究＊

LCAC-SW method has been extended to study the reaction dynamics for ion-pair formation processes.M+X₂M⁺+X^-₂ reaction system involves two potential energy surfaces,i.e.,the covalence state(M+X₂) and the ionic state(M⁺+X^-₂) and their crossing effect.The working equations for calculating state-to-state probability have been derived based on the above two-state model.The selected-state reaction probabilities of collinear ion-pair formation process M+I₂M⁺+I^-₂(M=Na,K,Cs) on Aten-Lanting-Los two-state potential energy surface have been calculated.The results show that the reaction probabilities are of resonance effect.     

Lifetimes of C-2 in rotational levels of the B̃2Σ+u state in the gas phase

Lifetimes of C^-₂ in rotational levels of the B?²Σ⁺_u:ν′ = 0, ν′ = 1 states have been measured. C^-₂ was produced from bromoacetylene and rare-gas metastables and the B?²Σ⁺_u—X?²Σ⁺_g transition was laser excited. The lifetimes are constant within a vibrational level, 77 = 8 ns for ν′= 0 and 73 = 7 ns for ν′ = 1. The oscillator strength f_νo = 0.044 ± 0.004.     

Kinetic-energy spectroscopy of high-rydberg fragments from keV collisions of H2+, D2+, N2+ and C2+ ions with rare-gas atoms

A method for measuring the kinetic-energy spectrum of high-Rydberg fragments from collisions of keV molecular ions with rare-gas atoms is described. The kinetic-energy spectra of high-Rydberg fragments from the collisions between D₂⁺, H₂⁺, N₂⁺ and C₂⁺ ions having 8 keV kinetic energy and thermal He and Xe are reported. Two single-collision processes for the generation of high-Rydberg fragments have been identified.     

Structure and Stability of Endohedral Complexes X@（HBNH）12

Using quantum chemistry methods B3LYP/6-31＋＋G（d,p） to optimize endohedral complexes X@（HBNH）12 （X=Li^0/＋, Na^0/＋, K^0/＋, Be^0/2＋, Mg^0/2＋, Ca^0/2＋, H and He）, the geometries with the lowest energy were achieved. Inclusion energy, standard equilibrium constant, natural charge, spin density, ionization potentials, and HOMO-LUMO energy gap were also discussed. The calculation predicted that X=Na^0/＋, K^0/＋, Mg^0/2＋, Ca^0/2＋, H and He are nearly located at the center of （HBNH）12 cluster. Li^＋ lies in less than 0.021 nm departure from the center. Li and Be^0/2＋ dramatically deviate from the center. （HBNH）12 prefers to enclose Li^＋, Be^2＋, Mg^2＋, and Ca^2＋ in it than others. Moreover, M@（HBNH）12 （M=Li, Na, K） species are ＂superalkalis＂ in that they possess lower first ionization potentials than the Cs atom （3.9 eV）.     

A theoretical study of the activation of methane by Gold(III) homoleptic complexes

The density functional theory method with the PBE functional, SBK pseudopotential, and extended basis sets was used to study the reaction between methane and gold(III) homoleptic complexes, namely, [AuX₄]^? (X = Cl, Br, I, H, CN, NH₂, OH, CH₃, and SH), [Au(X(CY)₂X)₂]^? (X = S, Y = H; X = Y = O), Au₂Cl₆, [Au(X₂(CY))₂]⁺ (X = S, Y = NH₂; X = O, Y = H), and [Au(acac)₂]⁺, with the formation of electrophic substitution products. The activation of methane under mild conditions was found to be uncharacteristic of anionic and neutral complexes. According to calculations of cationic oxygen-containing complexes, the formation of methane complexes is possible in their reactions with methane. The energy barrier to this reaction noticeably decreases because of the activation of the C-H bond in this complex. The heat effects vary widely depending on the nature of the ligand. There is, however, no obvious correlation between their values and the activation energy of the reaction.     

Metal Complexes of Free Radicals. Part II: Identification and structures of radical complexes of alkaline earth metals and zinc

The formation of chelate complexes between free radicals and closed-shell metal ions is observed by ESR. spectroscopy. High resolution spectra of 1:1 complexes formed between the radical anion of glyoxal-bis-(N-t-butylimine) (GLIR) and Mg²⁺, Ca²⁺ and Zn²⁺ are completely analysed. The complexes formed in dimethoxyethane or tetrahydrofuran solutions are Ca(GLIR)⁺, Mg(GLIR)X, Zn (GLIR)X and Zn(GLIR)Y^?₂, where X = Cl^?, Br^?, I^?, and Y = CN^?, NCS^?. The formation of the heterometallic, binuclear cyanide-bridged complex Zn(GLIR)Fe(CN)₆^3? is also described. Isotropic coupling constants are given for protons and ¹⁴N in GLIR as well as for the metal nuclei and magnetic nuclei in the groups X and Y. Stabilities, structures and ESR. parameters of these radical complexes are discussed.