Theory of the decay of molecular superexcited states

The decay processes of the superexcited state of a diatomic molecule are investigated theoretically. A general formula for the branching ratio for preionization and predissociation is derived using partitioning of the Green function. The predissociation and preionization probabilities per unit time are obtained in perturbation theory, employing the semiclassical theory and the local complex potential method based on the adiabatic vertical transition approximation for preionization. Some new features in the predissociation probability expression obtained are discussed. It is 0shown that the vibrational distribution of the molecular ions produced could be very different not only from that for the direct ionization transition, but also from that for the transition from an autoionizing state which does not couple to a dissociative state.     

Signature of electronic correlation in multi-electron emission from C60

Contrasting single to double-particle transition probabilities induced by a one-particle perturbation yields information on the strength of (two-particle) correlation in a system. Here, we calculate single and double ionization probabilities for a C₆₀ molecule upon the absorption of a single photon. We employ the Hartree–Fock and the frozen-core approximations for single-particle states and the random-phase approximation for the screened Coulomb interaction. Energy and angular dependencies of total and differential cross-sections are analyzed and the signature of the geometry of the fullerene and its charge-density response are pointed out.     

Nd,Yb, Au and UL-subshell ionization probabilities for 92 MeV Ar impact

The Nd, Yb, Au and UL-subshell X-ray emission probabilities as function of the impact parameter have been measured by X-ray—particle coincidence for 92 MeV Ar impact. The derivedL-subshell ionization probabilities show severe deviations from first order perturbation theory (SCA + corrections), although the totalL-shell ionization probabilities are still fairly well described by this approach. As is obvious from the data analysis, the discrepancy is due toL-substate coupling during the collision, which has a strong influence on the subshell ionization process, but is neglected in this theoretical approach. The observed influence of the multiple outer shell ionization on the measured data is also discussed.     

Importance of the interference effect in atomic excitation and ionization accompanying inner-shell vacancy creation

A theoretical model for electron excitation and ionization of atoms following inner-shell ionization is presented. Both the sudden creation of an inner-shell vacancy and the Coulomb interaction between the ionized electron and atomic electrons are taken into account. The transition amplitude is written as the sum of the conventional shake process and the multipole transition due to the Coulomb interaction between electrons. The valence-shell excitation and ionization probabilities accompanying K-shell photoionization of Ne are calculated. It is found that the interference between the shake process and the Coulomb interaction enhances the probabilities at low energies.     

Theory of multi-photon ionization and autoionization of SI

We present a theory and calculations of 3-photon ionization and autoionization of the silicon atom. We have employed a configuration interaction Hartree-Fock-Dirac method (CIHFD) in order to calculate energies and wavefunctions. The continuum wavefunctions have been obtained numerically and matched to Coulomb functions in the asymptotic region. Our results include energies of bound and autoionizing levels, dipole transition matrix elements, ionization and autoionization transition rates, obtained on the basis of perturbation theory.     

Density-functional theory with effective potential expressed as a direct mapping of the external potential: applications to atomization energies and ionization potentials

In this paper the authors further develop and apply the direct-mapping density functional theory to calculations of the atomization energies and ionization potentials. Single-particle orbitals are determined by solving the Kohn-Sham [Phys. Rev. A. 140, 1133 (1965)] equations with a local effective potential expressed in terms of the external potential. A two-parametric form of the effective potential for molecules is proposed and equations for optimization of the parameters are derived using the exchange-only approximation. Orbital-dependent correlation functional is derived from the second-order perturbation theory in its Moller-Plesset-type zeroth-order approximation based on the Kohn-Sham orbitals and orbital energies. The total atomization energies and ionization potentials computed with the second-order perturbation theory were found to be in agreement with experimental values and benchmark results obtained with ab initio wave mechanics methods.     

N2分子在强激光场中的场致电离

研究了在强激光脉冲中各种不同取向的N2分子发生场致电离的电离几率和表观电离效率.用量子化学方法计算了N2+分子离子在各种不同取向上的势能曲线,然后用传递矩阵方法得到了N2分子在不同方向上的电离几率,经过角度平均之后得到了各种取向的所有N2分子的总电离几率,并对计算结果进行了激光时间和空间修正.用800nm和70fs的激光脉冲对N2分子进行了在强激光场中的电离实验,得到了N2分子电离后产生的电子的角度分布图和电离几率随激光功率密度变化的关系曲线.实验结果和理论计算结果符合得很好.     

K-shell ionization in relativistic ion-atom collisions

We present calculations ofK-shell ionization probabilities in asymmetric ion-atom collisions at relativistic velocities of the projectile. The time-dependent Dirac equation is represented as a system of coupled differential equations. The transition probabilities are determined using the coordinate space method. This necessitates an extension of the angular momentum coupling compared with nonrelativistic collision systems. Effects of the relativistic projectile motion on the coupling matrix elements and their consequences onK-shell ionization are discussed.     

New relativistic ANO basis sets for transition metal atoms

New basis sets of the atomic natural orbital (ANO) type have been developed for the first, second, and third row transition metal atoms. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies, electron affinities, and excitation energies for all atoms and polarizabilities for spherically symmetric atoms. These calculations include spin-orbit coupling using a variation-perturbation approach. Computed ionization energies have an accuracy better than 0.2 eV in most cases. The accuracy of computed electron affinities is the same except in cases where the experimental values are smaller than 0.5 eV. Accurate results are obtained for the polarizabilities of atoms with spherical symmetry. Multiplet levels are presented for some of the third row transition metals.     

Ab initio studies on hydrogen-transfer tunneling for Cl + HCl abstraction hydrogen reaction

This article presents a treatment scheme of the tunneling of hydrogen between two molecular centers (Cl…Cl). The purpose is to calculate the tunneling probabilities of hydrogen atom transfer from the initial (the proceeding complex) to the final-state energy minima (the succeeding complex) in two anharmonic vibrational states (0 → 0 and 1 → 1) in terms of the time-dependent perturbation theory expression and to see whether spectroscopic signatures of tunneling persist in the form of splittings of the vibrational modes. The analysis uses the realistic potential energy function calculated at the HF/6−31 + G** self-consistent-field basis-set level for the interaction between transferred hydrogen and its molecular skeleton (Cl…H…Cl). This potential energy surface is calibrated by comparing its properties with those from sf-POLCI and the LEPS potential-energy surfaces. The anharmonic vibrational state is characterized by the corrected vibrational energy levels and a set of linear combination coefficients obtained via perturbation theory. The tunneling probabilities for two transitions (0 → 0 and 1 → 1) were calculated and compared with those from Gamow's equation. Applicability of the time-dependent perturbation theory expression and Gamow's equation to the [Cl BOND H…Cl] system is discussed. The vibrational splitting energies are obtained, and a spectroscopic signature caused by tunneling is expected and should be observable. © 1996 John Wiley & Sons, Inc.     

Correlation effects in a few-particle one-dimensional Coulomb-interacting system

Summary A model of the one-dimensional Coulomb-interacting few-particle system is studied in detail. The model is similar to a many-electron system which in a zero-order approximation of the non-interacting particles has only singly occupied one-electron levels. Such model cancels the divergencies in the Coulomb and exchange interaction energies found regularly for a conventional one-dimensional system which is built up of the doubly occupied one-electron levels and is submitted to the Coulomb perturbation. In the present case, the correlated wave functions for the system can be obtained from the Slater determinants constructed for the sets of the one-electron levels and combined according to the rules given by the standard perturbation theory. The calculations allow us to discuss the correlation influence and the effect of the size of the model on: (i) the excitation energies including the criterion corresponding to the metal-insulator transition (the Mott transition), (ii) the distribution of the correlated charge along the model, (iii) the average velocity of a two-particle system being in different states, and (iv) the dipole moments and transition probabilities. In the last case, the lifetime of the uncorrelated and correlated excited states obtained in the situation of the allowed one-photon transitions can be compared with the lifetime obtained for a similar system in the case when the one-photon transitions are forbidden and two-photon transitions should be taken into account. No data other than the length of the model and the fundamental constants of nature enter the calculations.     

Energy shifts in the relative coordinates treatment of the collinear collision between an atom and an oscillator. Exponential repulsive potential

The treatment of the kinetic term which may be taken as the perturbation when the collision between an atom and an oscillator is described with relative coordinates is shown to require the use of energy shifted basis functions in the calculation of the transition probabilities. For an exponential repulsive potential, a simple analytical formula is obtained for one quantum jumps in the first order Born approximation, which has a simple relationship with the first order Born distorted wave expression, and which lead to better results than the other available analytical formulas.     

共线散射体系A+BC的平-振能量传递──无限维李代数处理方法

利用无限维李代数方法处理了在BC分子能谱中含有二级与三级非简谐项的散射体系A＋BC的平-振能量传递问题，获得了散射过程的含有主要动力学参量的跃迁矩阵元和跃迁几率的解析表达式     

Fast-atom bombardment of the cyclic acetals: Evidence indicating the predominant involvement of condensed-phase processes in ionization

A series of cyclic acetals, the 2-phenyl-l,3 dioxolanes, and their deuterated analogues were studied by electron ionization (EI), chemical ionization (CI), and fast-atom bombardment (FAB) mass spectrometry to gain insight into the primary ionization processes for these compounds in FAB/liquid secondary ion mass spectrometry. Comparison of EI and CI data with that of FAB led to the conclusion that the predominant [M - H]+ ion observed in FAB for the nondeuterated cyclic acetals cannot to a large extent be rationalized in thermodynamic terms by known gas-phase ion-molecule reactions. Instead, a condensed-phase model in which the multicharged transition state for hydride abstraction is better solvated than the transition state for proton transfer appears to be a plausible explanation for the FAB data obtained for the nonlabeled cyclic acetals; however, this explanation is not entirely sufficient to rationalize the FAB data for the deuterated cyclic acetals. For these compounds, a dramatic time dependence of protonation versus hydride abstraction is observed that suggests that beam-induced reactive species are responsible for hydride abstraction in the condensed phase. This time dependence can be interpreted in terms of a buildup of highly reactive beam-induced species in the bulk of solution. Comparison of the results obtained for deuterated acetals with different surface activities support this hypothesis. (J Am Sot Mass     

Reactive scattering in hyperspherical coordinates

Preliminary results are presented for transition probabilities in the H + H₂ system derived from an adiabatic representation in terms of surface functions on hyperspheres. Special attention is given to the resonance structure for transition probabilities in the first vibrational level.     

The stationary phase method in the uniform WKB theory of inelastic scattering

When the modified Magnus approximation to the equation of motion in the uniform WKB theory of inelastic scattering is combined with the method of stationary phase for certain integrals, excellent numerical agreement is obtained between the transition probabilities thus calculated and the corresponding transition probabilities by the numerical solutions of the equation of motion and equivalent Schrödinger equations. The computation time required for calculation of transition probabilities is an order of magnitude less than that for numerical solution of Schrödinger equation by the Runge-Kutta-Gill method.     

Equilibrium geometry and electronic structure of benzylidene,arylethylidene, and heterocyclic arylidene malononitriles

The equilibrium geometry of some benzylidene, arylethylidene, and heterocyclic arylidene malononitriles has been calculated within the framework of the MNDO –MO formalism. Various structural factors are analyzed and discussed in terms of localized and delocalized MOS and π-interaction between methylene malononitrile (MMN) and aryl moieties. The possibility of charge transfer (CT ) from aryl to MMN moieties has been examined. The presence of a heterocyclic ring introduces a small perturbation into the MMN nuclear frame. p-Substituents have a pronounced effect on the magnitude and direction of the dipole moment. The variation of ionization potentials and bond order with the Hammet σ p are examined and a straight-line relationship is obtained. The correlation between physiological activity and quantum mechanical properties is analyzed in terms of heat of formation, ionization potential, dipole moment, and charge density on the aryl ring. © 1994 John Wiley & Sons, Inc.     

On the evolution equations for reduced density operators in quantum open systems

Evolution equations for transition probabilities of reduced density operators in quantum open systems are derived. Information contained in such equations is obtained from spectral resolutions and the role of memory kernels is elucidated within the scenario of many body theory as a function of the self-energy fields. As an analytical example of this formulation relaxation times for dissipative systems are evaluated in terms of the interaction between subsystems.