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This article shows a very satisfactory performance of the DFT Koopmans theorem analogue was demonstrated with respect to the energy intervals between the electronic levels of 4Me-BODIPY derivatives.

After ionization of an inner-valence electron of molecules, the resulting cation-radicals store substantial internal energy which, if sufficient, can trigger ejection of an additional electron in an Auger decay usually followed by molecule fragmentation. In the environment, intermolecular Coulombic decay (ICD) and electron-transfer mediated decay (ETMD) are also operative, resulting in one or two electrons being ejected from a neighbor, thus preventing the fragmentation of the initially ionized molecule. These relaxation processes are investigated theoretically for prototypical heterocycle-water complexes of imidazole, pyrrole, and pyridine. It is found that the hydrogen-bonding site of the water molecule critically influences the nature and energetics of the electronic states involved, opening or closing certain relaxation processes of the inner-valence ionized system. Our results indicate that the relaxation mechanisms of biologically relevant systems with inner-valence vacancies on their carbon atoms can strongly depend on the presence of the electron-density donating or accepting neighbor, either water or another biomolecule.

Three positional isomers of hydroxybenzoic acid, as well as phenol and benzoic acid, were studied using core-level photoemission and X-ray absorption spectroscopies, supported by quantum chemical calculations. While 2-hydroxybenzoic (salicylic) acid exists as a single conformer with an internal hydrogen bond, 3- and 4-hydroxybenzoic acids are mixtures of multiple conformers. The effects due to isomerism are clearly seen in the C 1s and O 1s photoelectron spectra, whereas the conformational effects on the binding energies are less pronounced. The O 1s photoelectron spectrum of salicylic acid is significantly different from that of the other two isomers, providing a signature of the hydrogen bond. In contrast, the oxygen K edge X-ray absorption spectra of the three hydroxybenzoic acids show only minor differences. The salicylic acid absorption spectrum at the carbon K edge shows a more resolved vibrational structure than the spectra of the other molecules, which can be explained in part by the existence of a single conformer. Our theoretical study of vibrational excitations in the lowest C 1s absorption bands of salicylic and 4-hydroxybenzoic acids indicates that the observed structure can be assigned to 0-0 lines of various electronic transitions since most of the totally symmetric vibrational modes with sufficiently large frequencies to be resolved are predicted to be inactive. Significant sensitivity of the C 1s excitations in 3-hydroxybenzoic acid to rotational conformerism was predicted but not observed due to spectral crowding.

Quinolines react with acylacetylenes and secondary phosphine chalcogenides at 20–75 °C to afford N-acylvinyl-2(1)-chalcogenophosphoryldihydroquinolines in good and excellent yields. Unlike the pyri...

Hybridogenesis in an interspecific hybrid frog is a coupling mechanism in the gametogenic cell line that eliminates the genome of one parental species with endoduplication of the remaining genome of the other parental species. It has been intensively investigated in the edible frog Pelophylax kl. esculentus (RL), a natural hybrid between the marsh frog P. ridibundus (RR) and the pool frog P. lessonae (LL). However, the genetic mechanisms involved remain unclear. Here, we investigated the water frogs in the western Russian territory. In three of the four populations, we genetically identified 16 RL frogs living sympatrically with the parental LL species, or with both parental species. In addition, two populations contained genome introgression with another species, P. bedriagae (BB) (a close relative of RR). In the gonads of 13 RL frogs, the L genome was eliminated, producing gametes of R (or R combined with the B genome). In sharp contrast, one RL male eliminated the L or R genome, producing both R and L sperm. We detected a variation in genome elimination within a population. Based on the genetic backgrounds of RL frogs, we hypothesize that the introgression of the B genome resulted in the change in choosing a genome to be eliminated. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This research was supported by JSPS and Russian Foundation for Basic Research (RFBR) under the Japan–Russia Research Cooperative Program (2018–2019), the Russian Foundation for Basic Research (grant no. 18-54-50013 to V.V.), and the program 211 of the Government of the Russian Federation (agreement no. 02.A03.21.0006). This study was performed within the framework of the state contract with the Institute of Plant and Animal Ecology, Ural Branch of the Russian Academy of Sciences.

Vibronic interactions in the pyridine radical cation ground state, 2A1, and its lowest excited states, 2A2 and 2B1, are studied theoretically. These states originate from the ionization out of the highest occupied orbitals of pyridine, 7a1 (nσ), 1a2 (π), and 2b1 (π), respectively, and give rise to the lowest two photoelectron maxima. According to our previous high-level ab initio calculations [Trofimov et al., J. Chem. Phys. 146, 244307 (2017)], the 2A2 (π−1) excited state is very close in energy to the 2A1 (nσ−1) ground state, which suggests that these states could be vibronically coupled. Our present calculations confirm that this is indeed the case. Moreover, the next higher excited state, 2B1 (π−1), is also involved in the vibronic interaction with the 2A1 (nσ−1) and 2A2 (π−1) states. The three-state vibronic coupling problem was treated within the framework of a linear vibronic coupling model employing parameters derived from the ionization energies of pyridine computed using the linear response coupled-cluster method accounting for single, double, and triple excitations (CC3). The potential energy surfaces of the 2A1 and 2A2 states intersect in the vicinity of the adiabatic minimum of the 2A2 state, while the surfaces of the 2A2 and 2B1 states intersect near the 2B1 state minimum. The spectrum computed using the multi-configuration time-dependent Hartree (MCTDH) method accounting for 24 normal modes is in good qualitative agreement with the experimental spectrum of pyridine obtained using high-resolution He I photoelectron spectroscopy and allows for some assignment of the observed features.

The third-order algebraic-diagrammatic construction method for studies of electron detachment processes within the electron propagator framework [IP-ADC(3)] was extended to treat the properties of molecular states with a detached electron using the intermediate state representation (ISR) formalism. The second-order ISR(2) equations for the one-particle (transition) density matrix have been derived and implemented as an extension of the IP-(U)ADC(3) method available in the Q-CHEM program. As a first systematic test of the present IP-(U)ADC(3)/ISR(2) method, the dipole moments of various electronic states of closed- and open-shell molecules have been computed and compared to full configuration interaction (FCI) results. The present study employing FCI benchmarks also provides the first rigorous estimates for the accuracy of electron detachment energies obtained using the IP-ADC(3) method.

Cell and gene damage caused by ionizing radiation has been studied for many years. It is accepted that DNA lesions (single- and double-strand breaks, for example) are induced by secondary species such as radicals, ions and the abundant low-energy secondary electrons generated by the primary radiation. Particularly harmful are dense ionization clusters of several ionization processes within a volume typical for the biomolecular system. Here we report the observation of a damage mechanism in the form of a non-local autoionizing process called intermolecular Coulombic decay (ICD). It directly involves DNA constituents or other organic molecules in an aqueous environment. The products are two energetic ions and three reactive secondary electrons that can cause further damage in their vicinity. Hydrogen-bonded complexes that consist of one tetrahydrofuran (THF) molecule—a surrogate of deoxyribose in the DNA backbone—and one water molecule are used as a model system. After electron impact ionization of the water molecule in the inner-valence shell the vacancy is filled by an outer-valence electron. The released energy is transferred across the hydrogen bridge and leads to ionization of the neighbouring THF molecule. This energy transfer from water to THF is faster than the otherwise occurring intermolecular proton transfer. The signature of the ICD reaction is identified in triple-coincidence measurements of both ions and one of the final state electrons. These results could improve the understanding of radiation damage in biological tissue. The authors study intermolecular Coulomb decay that occurs in a sample of THF and water in a reaction microscope employing triple-coincidence measurements of two ions and one electron. They find that ICD is a previously unconsidered effect between water and other organic molecules that are hydrogen-bonded, with ICD outpacing proton transfer.

Bacterial intoxication associated with inflammatory conditions during development can impair brain functions, in particular evolutionarily novel forms of memory, such as explicit learning. Little is known about the dangers of early-life inflammation on more basic forms of learning, for example, the acquisition of motor escape abilities, which are generally better preserved under pathological conditions. To address this limitation in knowledge, an inflammatory response was elicited in Wistar pups by lipopolysaccharide (LPS) injections (25 μg/kg) on postnatal days P15, P18 and P21. The acquisition of escape behaviour was tested from P77 by active avoidance footshock model and water maze. Open-field behaviour and blood corticosterone levels were also measured. Rat brain tissue was collected from pups 2 h post-injection and from adult rats which either underwent escape training on P77–P81 or remained untrained. mRNA levels of developmental brain plasticity factors MMP-9 and TIMP-1 were investigated in the medial prefrontal cortex and ventral/dorsal hippocampus. LPS-challenged rats displayed moderately deficient escape responses in both memory tests, increased freezing behaviour and, surprisingly, reduced blood cortisol levels. Mmp9 and Timp1, and their ratio to one another, were differentially altered in pups versus adult untrained rats but remained unchanged overall in rats trained in either learning task. Together, our data indicate that systemic pro-inflammatory response during early postnatal development has long-lasting effects, including on the acquisition of motor escape abilities and plasticity factor expression, into adulthood. Our data suggest that altered stress response could possibly mediate these deviations and repeated training might generate positive effects on plasticity under the employed conditions. Electronic supplementary material The online version of this article (doi:10.1007/s12640-017-9720-2) contains supplementary material, which is available to authorized users.

Experimental and quantum-chemical features of the triple nucleophilic substitution of halogen atoms in 2-chloro- and 2-bromopyridines under the action of P-centered nucleophiles generated in the system Pn/KOH/DMSO to afford tri(2-pyridyl)phosphine in a yield of up to 69% have been compared.

Quinolines react with acylacetylenes and secondary phosphine chalcogenides at 20-75 °C to afford N-acylvinyl-2(1)-chalcogenophosphoryldihydroquinolines in good and excellent yields. Unlike the pyridine-derived similar intermediates, which eliminate E-alkenes to give aromatic chalcogenophosphorylpyridines, thereby completing S

Valence photoelectron spectra and photoelectron angular distributions of trans-dichloroethene have been measured with vibrational resolution at photon energies between 19 eV and 90 eV. Calculations of photoelectron anisotropy parameters, β, and harmonic vibrational modes help provide initial insight into the molecular structure. The photon energy range encompasses the expected position of the atomic Cl 3p Cooper minimum. A corresponding dip observed here in the anisotropy of certain photoelectron bands permits the identification and characterization of those molecular orbitals that retain a localized atomic Cl character. The adiabatic approximation holds for the X 2Au state photoelectron band, but vibronic coupling was inferred within the A–B–C and the D–E states by noting various failures of the Franck–Condon model, including vibrationally dependent β-parameters. This is further explored using the linear vibronic coupling model with interaction parameters obtained from ab initio calculations. The A/B photoelectron band is appreciably affected by vibronic coupling, owing to the low-lying conical intersection of the A 2Ag and B 2Bu states. The C 2Bg band is also affected, but to a lesser extent. The adiabatic minima of the D 2Au and E 2Ag states are almost degenerate, and the vibronic interaction between these states is considerable. The potential energy surface of the D 2Au state is predicted to have a double-minimum shape with respect to the au deformations of the molecular structure. The irregular vibrational structure of the resulting single photoelectron band reflects the non-adiabatic nuclear dynamics occurring on the two coupled potential energy surfaces above the energy of their conical intersection.

The multi-configuration time-dependent Hartree (MCTDH) method was applied to study nuclear dynamics following transitions to a manifold of vibronically coupled ground 2A1 and excited 2A2 and 2B1 states of the pyridine radical cation (PRC). These states originate from ionization out of the highest occupied orbitals of pyridine, 7a1 (nσ), 1a2 (π), and 2b1 (π), respectively, and give rise to the lowest two photoelectron bands. We focus on various theoretical and computational aspects of the MCTDH method and methodology to calculate the spectrum, taking our study of the vibronically interacting 2A1, 2A2, and 2B1 states of PRC as an example. In particular, the choice of the single-particle functions (SPFs) and schemes to combine vibrational modes are discussed.

An earlier developed electron propagator method for the treatment of electron attachment to molecules within the non-Dyson algebraic-diagrammatic construction framework (EA-ADC) is extended by inclusion of the complex absorbing potential (CAP). The resulting method allows for the investigation of resonance states of metastable anions. Approximation schemes up to third-order perturbation theory for the electron propagator (EA-ADC(3)) are implemented. The CAP operator is treated up to second-order using the intermediate state representation formalism (ISR(2)) and the subspace projection technique. The CAP/EA-ADC(3) method is tested in first applications to the resonances in CO and N2 molecules associated with electron attachment to their low-lying π*-orbitals. The results of the calculations agree well with the available experimental and theoretical data and demonstrate the CAP-augmented EA-ADC modeling can become a useful tool for theoretical studies of metastable electron-attached states.

A topochemical reaction of pyrroles with bromotrifluoroacetylacetylene proceeds in solid Al2O3 at room temperature in two different directions depending on the substituent character at the nitrogen atom. While N-vinylpyrroles undergo the cross-coupling to give N-vinyl-2-(trifluoroacetylethynyl)pyrroles in up to 58% yield, unsubstituted NH-pyrroles add to the triple bond to afford exclusively E-2-(1-bromo-2-trifluoroacetylethenyl)pyrroles in 12–21% yields. It has been shown (1H NMR, quantum-chemical calculations) that the reaction is controlled by the strong intramolecular hydrogen bonding between NH and carbonyl groups.

The third-order non-Dyson algebraic-diagrammatic construction approach to the electron propagator [IP-ADC(3)] is extended using the intermediate state representation (ISR) formalism, allowing the wave functions and properties of molecular states with detached electron to be studied. The second-order ISR equations [ISR(2)] for the one-particle (transition) density matrix have been derived and implemented in the Q-CHEM program. The approach is completely general and enables evaluation of arbitrary one-particle operators and interpretation of electron detachment processes in terms of density-based quantities. The IP-ADC(3)/ISR(2) equations were implemented for Ŝz-adapted intermediate states, allowing open-shell molecules to be studied using unrestricted Hartree-Fock references. As a first test for computations of ground state properties, dipole moments of various closed- and open-shell molecules have been computed by means of electron detachment from the corresponding anions. The results are in good agreement with experimental data. The potential of IP-ADC(3)/ISR(2) for the interpretation of photoelectron spectra is demonstrated for the galvinoxyl free radical.

The electronic structure and optical properties of the isomeric difluoroboron β-diketonates, 2,2-difluoro-4-methylnaphtho-[2,1-e]-1,3,2-dioxaborin (I) and 2,2-difluoro-4-methylnaphtho-[1,2-e]-1,3,2-dioxaborin (II), were studied by means of X-ray photoelectron, absorption and luminescence spectroscopies. The experimental results were interpreted using high-level ab initio quantum chemical computations, including the algebraic-diagrammatic construction method for the polarization propagator of the second and third orders (ADC(2) and ADC(3)), the outer-valence Green's function (OVGF) method, and the time-dependent density functional (TDDFT) approach. The X-ray photoelectron measurements were assigned in the entire energy range using the results of the Kohn-Sham orbital calculations which employed the B3LYP functional. Pronounced hypsochromic shift of crystal-state fluorescence was observed in I upon the lowering of temperature, which can be explained by the deterioration of the conditions for excimers formation. According to our results, remarkable feature of II, absent in I, is its phosphorescence at room temperature. Basing on our calculations, a decay mechanism for the S1 state was proposed, explaining the observed differences in the phosphorescence of I and II.

International audience; The influence of vibronic coupling on the outer valence ionic states of cis-dichloroethene has been investigated by recording photoelectron spectra over the excitation range 19–90 eV using plane polarized synchrotron radiation, for two polarization orientations. The photoelectron anisotropy parameters and electronic state branching ratios derived from these spectra have been compared to theoretical predictions obtained with the continuum multiple scattering approach. This comparison shows that the photoionization dynamics of the à 2B2, B̃ 2A1, C̃ 2A2, and D̃ 2B1 states, all of which are formed through the ejection of an electron from a nominally chlorine lone-pair orbital, exhibit distinct evidence of the Cooper minimum associated with the halogen atom. While retaining a high degree of atomic character, these orbital ionizations nevertheless display clear distinctions. Simulations, assuming the validity of the Born-Oppenheimer and the Franck-Condon approximations, of the X̃ 2B1, à 2B2, and D̃ 2B1 state photoelectron bands have allowed some of the vibrational structure observed in the experimental spectra to be assigned. The simulations provide a very satisfactory interpretation for the X̃ 2B1 state band but appear less successful for the à 2B2 and D̃ 2B1 states, with irregularities appearing in both. The B̃ 2A1 and C̃ 2A2 state photoelectron bands exhibit very diffuse and erratic profiles that cannot be reproduced at this level. Photoelectron anisotropy parameters, β, have been evaluated as a function of binding energy across the studied photon energy range. There is a clear step change in the β values of the à 2B2 band at the onset of the perturbed peak intensities, with β evidently adopting the value of the B̃ 2A1 band β. The D̃ 2B1 band β values also display an unexpected vibrational level dependence, contradicting Franck-Condon expectations. These various behaviors are inferred to be a consequence of vibronic coupling in this system

A complete implementation of the polarization propagator based on the Dirac-Coulomb Hamiltonian is presented and applied to excitation spectra of various systems. Hereby the effect of spin-orbit coupling on excitation energies and transition moments is investigated in detail. The individual perturbational contributions to the transition moments could now be separately analyzed for the first time and show the relevance of one- and two-particle terms. In some systems different contributions to the transition moments partially cancel each other and do not allow for simple predictions. For the outer valence spectrum of the H2Os(CO)4 complex a detailed final state analysis is performed explaining the sensitivity of the excitation spectrum to spin-orbit effects. Finally, technical issues of handling double group symmetry in the relativistic framework and methodological aspects of our parallel implementation are discussed.

The photoabsorption spectra of C 4 H 4 O and C 4 D 4 O have been measured between ∼5.5 and 17.7 eV using a synchrotron radiation-based Fourier transform spectrometer. In addition to several broad bands due to transitions into valence states, the spectra exhibit numerous sharp bands associated with Rydberg states belonging to series converging onto the X 2 A 2 or the A 2 B 1 state limits. Vertical excitation energies and oscillator strengths have been computed using the second- and third-order algebraic-diagrammic construction polarisation propagator methods (ADC(2) and ADC(3)), and the equation-of-motion coupled-cluster method at the level of singles and doubles model (EOM-CCSD). Adiabatic excitation energies have been estimated using previously computed corrections. The theoretical predictions have allowed assignments to be proposed for the Rydberg series observed in the present single-photon absorption spectra and for some additional series, mainly of A 2 symmetry, reported in previous multiphoton excitation studies. The assignments of some of the Rydberg series converging onto the A 2 B 1 state limit have been revised and, guided by our calculations, the principal series is ascribed to the 2b 1 → n da 2 1 B 2 and 2b 1 → n db 1 1 A 1 transitions. f-type Rydberg series, previously observed only in the multiphoton absorption spectrum of furan, have been observed and assigned. Such f-type series, converging onto either the X 2 A 2 or the A 2 B 1 state thresholds, contribute significantly to the single-photon absorption spectrum. Many of the absorption bands associated with Rydberg states display vibrational progressions which resemble those in the corresponding photoelectron band. It appears that some of the structure associated with the 1a 2 → 3pb 2 1 B 1 and 1a 2 → 3pb 1 1 B 2 transitions involves excitation of non-totally symmetric vibrational modes.

Rare nonaromatic 3H-pyrroles have been synthesized from ketoximes having only one C–H bond adjacent to the oxime function and acetylene under pressure (10–13 atm) at 70 °C in two-phase superbase media of KOH/DMSO/n-hexane type, the yields ranging 8–36%. The effect of substituents, superbase nature and reaction conditions on yields of the target 3H-pyrroles has been analyzed. Hydroxypyrroline/3H-pyrroles interconversion as well as relative stability of model 3H-pyrroles have been assessed quantum chemically (MP2/6-31++G**//B3LYP/6-31G**).

The valence shell electronic structure and photoionisation dynamics of ortho-dichlorobenzene, ortho-bromochlorobenzene and trichlorobenzene have been investigated both experimentally and theoretica ...

Cross-coupling of NH-pyrroles with 1-bromo-2-(trifluoroacetyl) acetylene in the Al2O3 medium affords (E)-4-bromo-1,1,1-trifluoro-4-(pyrrol-2-yl)but-3-en-2-ones instead of the expected 2-ethynylated products. Quantum-chemical analysis shows strong intramolecular hydrogen bonding between NH and trifluoroacetyl groups, higher NH acidity and deeper charge transfer to the ethenyl moiety, which determines the reaction pathway.

The valence shell ionization spectrum of pyridine was studied using the third-order algebraic-diagrammatic construction approximation scheme for the one-particle Green’s function and the outer-valence Green’s function method. The results were used to interpret angle resolved photoelectron spectra recorded with synchrotron radiation in the photon energy range of 17–120 eV. The lowest four states of the pyridine radical cation, namely, 2A2 (1a 2 −1 1a2−1 ), 2A1(7a 1 −1 7a1−1), 2B1(2b 1 −1 2b1−1), and 2B2(5b 2 −1 5b2−1), were studied in detail using various high-level electronic structure calculation methods. The vertical ionization energies were established using the equation-of-motion coupled-cluster approach with single, double, and triple excitations (EOM-IP-CCSDT) and the complete basis set extrapolation technique. Further interpretation of the electronic structure results was accomplished using Dyson orbitals, electron density difference plots, and a second-order perturbation theory treatment for the relaxation energy. Strong orbital relaxation and electron correlation effects were shown to accompany ionization of the 7a1 orbital, which formally represents the nonbonding σ-type nitrogen lone-pair (nσ) orbital. The theoretical work establishes the important roles of the π-system (π-π* excitations) in the screening of the nσ-hole and of the relaxation of the molecular orbitals in the formation of the 7a1(nσ)−1 state. Equilibrium geometric parameters were computed using the MP2 (second-order Moller-Plesset perturbation theory) and CCSD methods, and the harmonic vibrational frequencies were obtained at the MP2 level of theory for the lowest three cation states. The results were used to estimate the adiabatic 0-0 ionization energies, which were then compared to the available experimental and theoretical data. Photoelectron anisotropy parameters and photoionization partial cross sections, derived from the experimental spectra, were compared to predictions obtained with the continuum multiple scattering approach.

The C 1s ionization spectrum of CH3I has been studied both experimentally and theoretically. Synchrotron radiation has been employed to record polarization dependent photoelectron spectra at a photon energy of 614 eV. These spectra encompass the main-line due to the C 1s single-hole state and the peaks associated with the shake-up satellites. Vertical ionization energies and relative photoelectron intensities have been computed using the fourth-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function and the 6-311++G** basis set. The theoretical spectrum derived from these calculations agrees qualitatively with the experimental results, thereby allowing the principal spectral features to be assigned. According to our calculations, two 2A1 shake-up states of the C 1s-1 σCI → σCI * type with singlet and triplet intermediate coupling of the electron spins (S' = 0, 1) play an important role in the spectrum and contribute significantly to the overall intensity. Both of these states are expected to have dissociative diabatic potential energy surfaces with respect to the C-I separation. Whereas the upper of these states perturbs the manifold of Rydberg states, the lower state forms a band which is characterized by a strongly increased width. Our results indicate that the lowest shake-up peak with significant spectral intensity is due to the pair (S' = 0, 1) of 2E (C 1s-1 I 5p → σCI *) states. We predict that these 2E states acquire photoelectron intensity due to spin-orbit interaction. Such interactions play an important role here due to the involvement of the I 5p orbitals.

A combined experimental and theoretical investigation has been performed to study the valence shell electronic structure and photoionisation dynamics of meta-dichlorobenzene and meta-bromochloroben ...

Depending on the substituent character at the nitrogen atom, pyrroles react acetylene (II) in two different directions.

The core level photoemission and near edge X-ray photoabsorption spectra of guanine in the gas phase have been measured and the results interpreted with the aid of high level ab initio calculations. Tautomers are clearly identified spectroscopically, and their relative free energies and Boltzmann populations at the temperature of the experiment (600 K) have been calculated and compared with the experimental results and with previous calculations. We obtain good agreement between experiment and the Boltzmann weighted theoretical photoemission spectra, which allows a quantitative determination of the ratio of oxo to hydroxy tautomer populations. For the photoabsorption spectra, good agreement is found for the C 1s and O 1s spectra but only fair agreement for the N 1s edge.

The valence shell photoelectron spectra of uracil, 1-methyluracil and 6-methyluracil have been studied experimentally and theoretically. Synchrotron radiation has been used to record spectra at photon energies of 40 and 80 eV. Photoelectron angular distributions have been determined and these provide an experimental means of distinguishing between σ- and π-type orbitals. Vertical ionization energies and spectral intensities have been evaluated using the many-body Green’s function approach, thereby enabling theoretical photoelectron spectra to be derived. The calculated spectra display a satisfactory agreement with the experimental data and this has allowed most of the photoelectron bands to be assigned. Two of the outer-valence vertical ionization energies are similar to one another and the vibrational progressions associated with these transitions overlap strongly. Vibronic interaction between these states, induced through the excitation of out-of-plane vibrational modes, may lead to nonadiabatic effects. Preliminary theoretical investigation of this interaction has been performed.

Valence shell photoelectron spectra of the 5-halouracils have been recorded using synchrotron radiation at photon energies of 40 and 80 eV. Photoelectron angular distributions have been determined and these provide an experimental means of deducing the extent to which the molecular orbitals possess predominantly σ, π or halogen np character. In chloro-, bromo- and iodouracil two peaks, associated with the essentially halogen atom lone-pair orbitals, have been observed. The separation between these peaks, and the value of their photoelectron asymmetry parameters at an excitation energy of 40 eV, are compared with results for the corresponding orbitals in the halobenzenes and halothiophenes. Vertical ionisation energies and spectral intensities have been evaluated using the many-body Green’s function approach, thereby enabling theoretical spectra to be derived. Assignments have been proposed for most of the structure observed in the valence shell photoelectron spectra based upon the available experimental and theoretical evidence.

The ionization spectra of furan, pyrrole, thiophene, and selenophene have been calculated within the framework of the nonempirical quantum-chemical method with the Green's one-particle function in the approximation of the third order algebraic diagram construction [ADC(3)]. The calculated energies and the intensity of vertical transitions pertaining to the ionization of outer and inner shells are compared with the newest experimental data. The good agreement of theoretical and experimental results enabled a detailed assignment and interpretation of the observed photoelectron spectra to be carried out. Problems of disturbing the picture of orbital ionization are considered; the mechanism of formation of low-lying photoelectron satellites is explained. Certain general rules and trends of the behavior of the spectra of the systems studied are considered.

The first highly efficient, diastereo- and regioselective transition metal-catalyzed addition of metal hydrides (stannanes, silanes, and germanes) and bimetallic species (ditins and silyltins) to cyclopropenes has been developed. It was shown that the addition across the double bond of cyclopropenes is generally controlled by steric factors and proceeds from the least hindered face. This methodology represents a powerful and atom-economic approach toward a wide variety of highly substituted stereodefined cyclopropylmetals, useful building blocks unavailable by other methods.

The photoelectron spectrum of selenophene has been recorded using synchrotron radiation in the photon energy range 20–80 eV and the inner valence region has been studied in detail for the first time. Green's function methods have been employed to evaluate the energies and spectral intensities of all valence shell ionization transitions and the results have facilitated an interpretation of the experimental spectra. Strong configuration interaction results in a redistribution of the intensity associated with the low lying π1(1b1) orbital amongst several satellite states located in the outer valence region. The continuum multiple scattering approach has been used to calculate photoelectron asymmetry parameters for selenophene, thiophene and hydrogen sulphide, and these theoretical predictions have been compared with the corresponding experimental data to assess the influence of Cooper minima and shape resonances. The comparison indicates that the Se 4p and the S 3p Cooper minima have little effect on the valence shell photoionization dynamics of selenophene and thiophene, respectively. This outcome is discussed in connection with the closely related hydrogen selenide and hydrogen sulphide molecules where strong resonant phenomena are observed.

Ab initio calculations are performed to explain the discrete transitions in experimental C 1s-NEXAFS (near edge X-ray absorption fine structure) spectra of various benzoic acid derivates. Transition energies and oscillator strengths of the contributing C 1s–π * excitations are computed using the ADC(2) (second-order algebraic-diagrammatic construction) method. This method is demonstrated to be well suited for the finite electronic systems represented by these simple organic acids. There is good agreement between experiment and theory reproducing all the relevant spectral features. Some transitions can only be assigned based on a theoretical foundation. Remaining discrepancies between experimental and computed spectra are discussed.

Angle resolved photoelectron spectra of the X̃(2)B1, Ã(2)A2, B̃(2)B2, and C̃(2)B1 states of bromobenzene have been recorded over the excitation range 20.5-94 eV using linearly polarized synchrotron radiation. The photoelectron anisotropy parameters and electronic branching ratios derived from these spectra have been compared to theoretical predictions obtained with the continuum multiple scattering approach. This comparison shows that ionization from the 8b2 orbital and, to a lesser extent, the 4b1 orbital is influenced by the Cooper minimum associated with the bromine atom. The 8b2 and 4b1 orbitals are nominally bromine lone-pairs, but the latter orbital interacts strongly with the π-orbitals in the benzene ring and this leads to a reduced atomic character. Simulations of the X̃(2)B1, B̃(2)B2, and C̃(2)B1 state photoelectron bands have enabled most of the vibrational structures appearing in the experimental spectra to be assigned. Many of the photoelectron peaks exhibit an asymmetric shape with a tail towards low binding energy. This asymmetry has been examined in the simulations of the vibrationally unexcited peak, due mainly to the adiabatic transition, in the X̃(2)B1 state photoelectron band. The simulations show that the asymmetric profile arises from hot-band transitions. The inclusion of transitions originating from thermally populated levels results in a satisfactory agreement between the experimental and simulated peak shapes.

The valence-shell ionization spectrum of bromobenzene, as a representative halogen substituted aromatic, was studied using the non-Dyson third-order algebraic-diagrammatic construction [nD-ADC(3)] approximation for the electron propagator. This method, also referred to as IP-ADC(3), was implemented as a part of the Q-Chem program and enables large-scale calculations of the ionization spectra, where the computational effort scales as n(5) with respect to the number of molecular orbitals n. The IP-ADC(3) scheme is ideally suited for investigating low-lying ionization transitions, so fresh insight could be gained into the cationic state manifold of bromobenzene. In particular, the present IP-ADC(3) calculations with the cc-pVTZ basis reveal a whole class of low-lying low-intensity two-hole-one-particle (2h-1p) doublet and quartet states, which are relevant to various photoionization processes. The good qualitative agreement between the theoretical spectral profile for the valence-shell ionization transitions generated with the smaller cc-pVDZ basis set and the experimental photoelectron spectrum measured at a photon energy of 80 eV on the PLEIADES beamline at the Soleil synchrotron radiation source allowed all the main features to be assigned. Some theoretical aspects of the ionization energy calculations concerning the use of various approximation schemes and basis sets are discussed.

A polarization propagator method, referred to as algebraic-diagrammatic construction (ADC), is extended to the treatment of static and dynamic response properties of molecules. The recent intermediate state representation (ISR) concept of the ADC theory, giving direct access to excited states wave functions and properties, allows us to derive simple closed-form expressions for linear and higher response functions. The use of the band-Lanczos algorithm is proposed to evaluate efficiently the resolvent type ADC expressions. The performance of the method is tested in computations of static and dynamic polarizabilities of several small molecules at the second-order (ADC(2)) level of the theory. The ADC(2) results are compared with those of full configuration interaction (FCI), coupled cluster (CC), and SOPPA (second-order polarization propagator approximation) treatments.

The complete valence shell photoelectron spectra of cytosine, thymine and adenine have been investigated experimentally and theoretically. Vertical ionization energies and spectral intensities have been evaluated using the many-body Green's function method, thereby enabling theoretical photoelectron spectra to be derived. In cytosine, the influence of tautomers and rotational conformers has been investigated. The calculated spectra display a satisfactory agreement with the experimental data and this has allowed most of the photoelectron bands to be assigned. Photoelectron asymmetry parameters have been determined from angle resolved spectra recorded with synchrotron radiation. The experimental data show that the electronic configuration of the five outer orbitals in cytosine, thymine and adenine is π, σ, π, σ, π. Vertical ionization energies have been measured for all the outer-valence orbitals even though some of the associated bands overlap significantly.

A new relaxation pathway of optically allowed valence-excitations in molecules bound to metal atoms was investigated. We show that the σnonπ* excitation of HCN in MgnHCN (n = 1,2) clusters decays through the emission of an electron from the metallic component. The calculated lifetimes are of the order of 140 fs for MgHCN and 25 fs for Mg2HCN. These short lifetimes suggest that the relaxation mechanism discussed here should dominate for molecules adsorbed on metal clusters or surfaces. We find that at large distances this decay is dominated by energy transfer.

The photoelectron spectrum of hydrogen selenide has been recorded using synchrotron radiation in the photon energy range 15–110 eV and the inner valence region has been studied in detail for the first time. Green’s function methods have been employed to evaluate the ionisation energies and spectral intensities of all valence states and the results have facilitated an interpretation of the experimental spectra. Two outer valence satellites have been observed at binding energies of ∼17 and ∼18.5 eV. The continuum multiple scattering (CMS-Xα) approach has been used to calculate photoelectron asymmetry parameters and branching ratios for the outer valence orbitals and these have been compared with experimental data. The Se 4p Cooper minimum strongly affects the photoionisation dynamics of the outermost 4b 1 orbital and its influence is evident in both the theoretically predicted and the measured asymmetry parameter for the X ˜ 2 B 1 state. The experimental data for the A ˜ 2 A 1 and B ˜ 2 B 2 state asymmetry parameters also display energy dependent variations in the vicinity of the Cooper minimum. However, for these two states the agreement between the predicted and observed asymmetry parameters is less satisfactory. The present results for H 2 Se have been compared with similar data for the closely related H 2 S molecule.

The complete valence shell photoelectron spectrum of tetrafluoromethane has been recorded using synchrotron radiation and the observed structure has been interpreted using ionisation energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green’s function and the outer valence Green’s function (OVGF) method. The ADC(3) calculations were performed using both the original variant based on the Dyson equation and the recently proposed non-Dyson scheme. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence 2t2 and 3a1 orbitals is strongly influenced by reorganisation effects and the intensity is spread amongst numerous satellites. Highly resolved spectra have been measured for the C ∼ 2 T 2 and the D ∼ 2 A 1 states, and the vibrational structure has been associated primarily with excitation of the ν 1 + ( a 1 ) mode. However, the analyses also provide evidence for excitation of the Jahn-Teller active ν 2 + ( e ) mode in the C ∼ 2 T 2 state, and the ν 3 + ( t 2 ) mode in the D ∼ 2 A 1 state. Excitation of this latter mode can be explained in terms of vibronic coupling between the C ∼ 2 T 2 and the D ∼ 2 A 1 states. Photoelectron angular distributions and branching ratios have been determined and demonstrate that shape resonances affect the outer valence shell photoionisation dynamics. The experimental results are compared with previous theoretical predictions but a consistent interpretation has not been obtained. The major difficulty concerns the uncertainty in the locations of valence shell transitions into the 5a1 and the 5t2 virtual orbitals.

Silicon-nitrogen bonding and the photoelectron spectra of hydro-silatrane and methyl-silatrane, XSi[OCH2CH2]3N (X = H and Me), were studied with ab initio electron propagator theory, many-body methods, and density functional models. A linear vibronic coupling (LVC) model was employed to estimate vibrational widths of the ionization bands and to study the dependence of the ionization energies on the molecular geometry. Particular attention was given to coordinates that change the Si-N distance and the strength of the donor-acceptor interaction between these two atoms. The ionization energy of the highest occupied molecular orbital has a very strong geometrical dependence which leads to an unusually large vibrational width in the corresponding photoelectron band. The assignment of this band in methyl-silatrane, which was controversial for a long time, is resolved by the present study. The calculated photoelectron spectra allow for clear assignment of at least three more bands in the observed spectra. The present results demonstrate the important role of electrostatic interactions in Si-- N bonding and in the outer-valence ionization energies of the silatranes.

International audience; The excitation spectra and molecular dynamics of furan associated with its low-lying excited singlet states 1A2(3s), 1B2(V), 1A1(V'), and 1B1(3p) are investigated using an ab initio quantum-dynamical approach. The ab initio results of our previous work [J. Chem. Phys. 119, 737 (2003)] on the potential energy surfaces (PES) of these states indicate that they are vibronically coupled with each other and subject to conical intersections. This should give rise to complex nonadiabatic nuclear dynamics. In the present work the dynamical problem is treated using adequate vibronic coupling models accounting for up to four coupled PES and thirteen vibrational degrees of freedom. The calculations were performed using the multiconfiguration time-dependent Hartree method for wave-packet propagation. It is found that in the low-energy region the nuclear dynamics of furan is governed mainly by vibronic coupling of the 1A2(3s) and 1B2(V) states, involving also the 1A1(V') state. These interactions are responsible for the ultrafast internal conversion from the 1B2(V) state, characterized by a transfer of the electronic population to the 1A2(3s) state on a time scale of approximately 25 fs. The calculated photoabsorption spectrum of furan is in good qualitative agreement with experimental data. Some assignments of the measured spectrum are proposed.

The multi-mode and multi-state vibronic interactions in the heterocyclic molecules furan, pyrrole, thiophene and their radical cations are investigated theoretically, employing a linear vibronic coupling scheme. The underlying system parameters are determined from large-scale ab initio computations. Previous time-independent dynamical calculations on the radical cations are extended by wave-packet propagations (using the MCTDH method) confirming the strong nonadiabatic coupling effects. For the singlet excited states of furan and thiophene quantum dynamical calculations are presented which go beyond the two-state approximation frequently applied in the literature. The characteristic spectral structures are well reproduced, especially in the case of furan. The implications of these results on the photochemical reaction dynamics of these species are discussed.

2 (V), 1 A 1 (V8), respectively, at the C 2v ground-state molecular configuration# have been studied using the equation-of-motion coupled-cluster singles and doubles method ~EOM-CCSD!. Full geometry optimizations with subsequent computation of harmonic vibrational frequencies have been performed in order to locate and characterize stationary points on the potential energy surfaces ~PES!. The latter optimization work was enabled by the availability of analytic energy gradient techniques for the EOM-CCSD approach. A major new finding is that both the 1 B2(V) and 1 A1(V8) valence states are unstable with respect to non-totally symmetric distortions at the C2v configuration. The symmetry breaking in the 1 B2(V) state involves an in-plane coordinate of b2 symmetry. The relaxation process begins on the S2 adiabatic PES and, after passing through a conical intersection of the S2 and S1 PES, continues on the S1 surface, taking the system finally to the adiabatic minimum ofS1 ( 1 A2 state!. The 1 A1(V8) valence state is found to be unstable with respect to the out-of-plane bending coordinates of b1 and a2 symmetry. The resulting relaxed molecular structures have Cs and C2 symmetry, respectively. The present findings are analyzed in terms of a linear vibronic coupling model and spectroscopic implications are discussed. © 2003 American Institute of Physics. @DOI: 10.1063/1.1578051#

The valence shell photoelectron spectrum of purine has been studied experimentally and theoretically. Synchrotron radiation has been used to record spectra at photon energies of 45 and 85 eV. Photoelectron angular distributions have been determined and these provide an experimental means of distinguishing between σ-and π-type orbitals. Vertical ionization energies and photoelectron spectral intensities have been evaluated using the many-body Green function method. The calculated spectra agree well with the experimental results in the outer valence region and have proved to be indispensable for interpreting the structure at higher binding energies where the single particle model of ionization breaks down. The photoelectron spectrum of pyrimidine has also been studied and is compared to that of purine.

The valence shell photoelectron spectrum of 2-iodothiophene (2-I-Th) has been studied experimentally and calculations have been carried out to characterize the main bands due to single-hole ionized states for both 2- and 3-iodothiophene. The importance of electron correlation in the formation of satellite states has also been assessed. The vertical ionization energies and spectral intensities of the entire valence shell photoelectron spectrum have been computed using the third-order algebraic–diagrammatic construction approximation for the one-particle Green function. These theoretical predictions have allowed assignments to be proposed for all the prominent structure observed in the experimental spectra, and have highlighted the breakdown of the molecular orbital model of ionization for the π1-orbital. By comparing the present theoretical and experimental results for iodothiophene with similar data for chloro-and bromothiophene, it has been found that the binding energies and intensities of the satellites associated with the π1-orbital form a pattern which is common to all three monohalothiophenes. Relativistic Hartree–Fock calculations have been carried out to investigate the importance of such effects on the valence shell ionization of iodothiophene. Synchrotron radiation has been used to measure photoelectron angular distributions and branching ratios of 2-I-Th. The spectral behaviour of the asymmetry parameters has provided an experimental means of distinguishing photoelectron bands due to σ-orbitals from those associated with π-orbitals. A high-resolution photoelectron spectrum of the outer valence shell of 2-I-Th has been recorded using HeI radiation, and vibrational structure has been observed and analysed in the 2A'', A 2A'', 2A' and 2A'' state bands.

A recently developed consistent third-order propagator method for the treatment of electronic excitation in molecules is tested in first applications. The method referred to as third-order algebraic-diagrammatic construction [ADC(3)] extends the existing second-order approximation and aims at a more accurate computation of excitation energies and transition moments than afforded at the second-order level. For a stringent test of the method we compare the ADC(3) energies for over 40 singlet and triplet vertical transitions in H2O, HF, N2, and Ne with the results of recent full configuration interaction (FCI) and coupled cluster (CC) computations. The ADC(3) results reflect a substantial and uniform improvement with respect to the second-order description. The mean absolute deviation of the single excitation energies from the FCI results is below 0.2 eV. Although this does not equal the accuracy of the third-order CC3 model, the ADC(3) method, scaling as N6 with the number of orbitals, may be viewed as a good compromise between accuracy and computational cost.