Quantum beats and Kepler motion in fast competing photoionization and photodissociation processes

Electronic and nuclear wavepackets created by coherent excitation of an autoionized and predissociated 'complex' resonance in H2 are studied theoretically using time-dependent multichannel quantum defect theory. The calculations predict that quantum beats between the components of the complex resonance interfere with Rydberg wavepacket (Kepler) motion to yield characteristic 'mixed' flux patterns in the observable time-dependent ionization and dissociation signals.     

Expanded electronic states of the fluorine molecule

Potential curves of electronically excited states of F₂ with an expanded outer orbital have been calculated using a modified frozen core technique: The ionic core has been described with a two-determinant wave function and for the excited states a mixing of configurations with different cores has been employed. An investigation of the valence shell states of F₂ is presented and potential curves for a singly excited as well as a doubly excited V-state of ¹Σ_u⁺ symmetry have been calculated. Further a low lying two-configuration state resulting from simultaneous excitation to a valence and a Rydberg orbital is predicted.     

Application of the virial theorem to the study of molecular electronic wave functions

With aid of the virial theorem formulated for the energy differences of two electronic states some theorems on the wave functions of diatomic molecules have been proven. It is shown how proper Rydberg states can be distinguished from other electronic states with a diffuse outer orbital by virtue of the virial theorem and that a singlet-triplet pair of excited states cannot have the same equilibrium geometry and identical orbitals simultaneously. Furthermore if the two states have the same dissociation limit a theorem on the differences of the kinetic and the potential energy can be derived which allows an understanding of the shape of the electronic wave functions. As an application the wave functions and the ordering of the lowest states of H ₂ ⁺ and H₂ have been discussed.This work is part of the project Nr. SR 2.159.74 of the Schweizerischer Nationalfonds.     

Hartree-fock calculations for excited rydberg states

A method is introduced which allows to compute self-consistent restricted Hartree-Fock wave functions for excited Rydberg configurations. The concepts of reorganization and electron correlation of Rydberg states are discussed. As an illustration Hartree-Fock calculations for the (ls)(nl) Rydberg series of He are presented.     

S‐Trifluoromethylation of Thiols by Hypervalent Iodine Reagents: A Joint Experimental and Computational Study

The radical trifluoromethylation of thiophenol in condensed phase applying reagent 1 (3,3‐dimethyl‐1‐(trifluoromethyl)‐1λ³,2‐benziodoxol) has been examined by both theoretical and experimental methodologies. On the basis of ab initio molecular dynamics and metadynamics we show that radical reaction mechanisms favourably compete with polar ones involving the S‐centred nucleophile thiophenol, their free energies of activation, ΔF^≠, lying between 9 and 15 kcal mol^?1. We further show that the origin of the proton activating the reagent is important. Hammett plot analysis reveals intramolecular protonation of 1 , thus generating negative charge on the sulfur atom in the rate‐determining step. The formation of a CF₃ radical can be thermally induced by internal dissociative electron transfer, its activation energy, ΔF^≠, amounting to as little as 10.8 and 2.8 kcal mol^?1 for reagent 1 and its protonated form 2 , respectively. The reduction of the iodine atom by thiophenol occurs either subsequently or in a concerted fashion.     

Bending energy level structure and quasilinearity of the X+ 3B1 ground electronic state of NH2+

The bending level structure of the quasilinear X+ 3B1 ground electronic state of the amidogen cation NH2+ was studied by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy using a near-infrared vacuum-ultraviolet two-photon ionization sequence via selected rovibronic levels of the A 2A1 state of NH2. The careful selection of the intermediate levels permitted to optimize the transition intensities to the lowest vibrational levels of the cation in the photoionization step and to overcome the low sensitivity of previously employed single-photon ionization schemes. For the first time, all bending levels of the cationic ground state with quantum numbers upsilon2,lin + < or =4, N+ < or =4, and /K+/ < or =2 could be observed, enabling a detailed characterization of the large-amplitude bending vibration. The rotational structure corresponds to that of an effectively linear molecule in all observed vibrational levels. The bending vibrational structure which shows marked deviations from a harmonic behavior was analyzed in terms of a semirigid bender model. The bending potential function was obtained from a fit to the experimental data. The height of the barrier at the linear geometry and the bond angle at the potential minimum were determined to be 231.8(22) cm(-1) and 152.54(4) degrees , respectively, and all bending levels are located above the maximum of the barrier.     

Application of the independent electron pair approach to the calculation of excitation energies,ionization potentials,and electron affinities of first row atoms

Excitation energies, first ionization potentials and electron affinities of first row atoms are calculated with a spin-adapted independent electron pair approximation (IEPA) combined with the direct determination of pair natural orbitals (PNOs). To enable comparison with molecular calculations Gaussian basis sets are used which are small enough to be also applicable to molecules. IEPA results for the above mentioned properties are accurate to 0.1–0.3 eV which is almost one order of magnitude better than the corresponding SCF-results. The same accuracy can be expected for molecules in which a localization of the doubly and singly occupied orbitals is possible, for instance for small hydrides. This is supported by the results of calculations on carbon hydrides.     

Pariser-Parr-Pople-Rechnungen mitσ- undπ-Basisorbitalen

Zusammenfassung Energie and Ladungsverteilung desn –*-Zustandes von Formaldehyd wurde mit Konfigurationswechselwirkung, nach der restricted open shell SCF-Methode and mit einem Verfahren der iterierten Störungsrechnung im Rahmen der PPP-Näherung untersucht. Mit den beiden letztgenannten Methoden ergab sick ein Dipolmoment, welches gut mit dem experimentellen Wert übereinstimmt.

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The energy and the dipole moment have been calculated for then –*-state of formaldehyde by configuration interaction, by the restricted open shell SCF method and by a method of iterated perturbation theory using the PPP-approximations. With the latter two methods a value for the dipole moment is obtained which agrees well with experiment.

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Resume L'énergie et la distribution de charges ont été calculés pour l'étatn –* du formaldehyde par la méthode d'interaction de configurations, la méthode SCF restricted open shell et par une méthode itérative de perturbations, selon les approximations PPP. Les deux derniéres méthodes fournissent une valeur pour le moment dipolaire qui est en bon accord avec l'expérience.

     

Electronic structural and magnetic properties of cadmium chalcogenide beryllosilicate sodalites

Density functional self-consistent spin-polarized calculations with the Discrete Variational Method were performed to obtain the electronic structures of cadmium chalcogenide beryllosilicate sodalites Cd₈[BeSiO₄]₆Z₂ and their bulk materials CdZ (Z = S, Se, Te). Similar as their bulk materials, these sodalites are also semiconductors. From their density of states and charge distributions, it was found that there is greater localization of the electron density in the sodalites compared with that of the bulk. The band gaps in their bulk compounds are different from those in the sodalite structures due to the electrons of Si, Be and O filled in. Different from their bulk materials, the d electrons of Cd play an important role to form an unseparated valence band with all orbitals of other elements. The calculated magnetic moments of these three materials are very small since all d atomic orbitals are fully occupied. Received: 28 March 1997 / Revised: 18 July 1997 / Accepted: 9 September 1997