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The dissociations of nascent Fe(CO)5++ ions created by 40.81 eV photoionization of iron pentacarbonyl have been examined using threefold and fourfold electron–ion coincidence measurements. The energies and forms of the ions have been explored by high-level calculations, revealing several new structures. The most stable form of Fe(CO)5++ has a quite different geometry from that of the neutral molecule. The dissociation pattern can be modeled as a sequence of CO evaporations followed by two-body charge separations. Each Fe(CO)n++ (n = 1–4) dication is stable in a restricted energy range; as its internal energy increases, it first ejects a neutral CO, then loses CO+ by charge separation at higher energy. In the initial stages, charge-retaining CO evaporations dominate over charge separation, but the latter become more competitive as the number of residual CO ligands decreases. At energies where ionization is mainly from the CO ligands, new Fe–C and C–C bonds are created by a mechanism which might be relevant to catalysis by Fe., Dissociations of nascent Fe(CO)5++ ions by sequential CO evaporations, leading (in restricted energy ranges) to stable Fe(CO)n++ (n = 1−4) dicationic species. At energies where ionization is mainly from the CO ligands, new Fe−C and C−C bonds are created by a mechanism which might be relevant to catalysis by Fe.

We use accurate ab initio methodologies at the coupled cluster level ((R)CCSD(T)) and its explicitly correlated version ((R)CCSD(T)-F12) to investigate the electronic structure, relative stability, and spectroscopy of the stable isomers of the [S2O2] system and of some of its cations and dications, with a special focus on the most relevant isomers that could be involved in terrestrial and planetary atmospheres. This work identifies several stable isomers (10 neutral, 8 cationic, and 5 dicationic), including trigonal-OSSO, cis-OSSO, and cyc-OSSO. For all these isomers, we calculated geometric parameters, fragmentation energies, and simple and double ionization energies of the neutral species. Several structures are identified for the first time, especially for the ionic species. Computations show that in addition to cis-OSSO and trans-OSSO proposed for the absorption in the near-UV spectrum of the Venusian atmosphere other S2O2, S2O2+, and S2O22+ species may contribute. Moreover, the characterization of the stability of singly and doubly charged S2O2 entities can also be used for their identification by mass spectrometry and UV spectroscopy in the laboratory or in planetary atmospheres. In sum, the quest for the main UV absorber in Venus' atmosphere is not over, since the physical chemistry of sulfur oxides in Venus' atmosphere is far from being understood.

We carried out a theoretical, fully ab initio, investigation of the stable forms of the [H,C,N,O,O] pentatomic molecular system, whose isomers are involved in fundamental combustion and atmospheric processes and are of potential interest for astrophysics. By adopting the MP2 and CCSD(T) electronic structure methods, combined with extrapolations to the complete basis set (CBS) limit, we characterized 20 low-energy isomers, excluding weak van der Waals complexes. For these molecules, we determined a set of geometrical parameters, relative energies, anharmonic vibrational frequencies, IR intensities, and fragmentation/formation energies from various atomic and/or molecular fragments. We discuss the relevance of the present findings for the search of new molecular species in astrophysical and atmospheric media and give suggestions for their possible detection in laboratory experiments. The set of data provided by the present work should facilitate the identification of these species from their gas-phase and low-temperature solid matrix spectra, whenever measured.

By using first-principles approaches based on Density Functional Theory, we explore the possibility of using dendritic macromolecular structures as carriers of the doxorubicin anticancer drug. In particular, we consider macromolecular cavities of different sizes composed of phenylene-, thiophene-, phenyl-cored thiophen- and thioazole-based dendrimers. The comparison between the optimized molecular geometries of the monomers and of the host-guest complexes reveals that only slight structural changes are observed in doxorubicin upon complexation. Also, the encapsulation energies for the host-guest complexes suggest that these systems are of potential use for pharmacology applications in vivo. The interaction of the guest doxorubicin with the macromolecular cavities exploits different types of weak intermolecular forces including σ, π and hydrogen bond interactions. The electronic structure of these complexes is discussed, with particular emphasis placed on the role of the charge distribution and the nature of the frontier molecular orbitals in the encapsulation process. Spectroscopic properties of these complexes are derived to facilitate their detection in laboratory and in vivo. These include IR vibrational frequencies, absorption wavelengths and relative oscillator strengths for the main transitions in the UV-Vis spectrum.

We present a theoretical study of the ground electronic state potential of the Ca+Ar2 complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220 K. These calcu...

Using an ab initio methodology and mass spectrometric study we identify AuO2+ as a metastable species in the gas phase. This represents the first characterization of a gas phase compound of gold with the oxidation state +4. Computations show that this dication exhibits deep potential wells with long lived electronic states. Its electronic ground state is of 4∑- symmetry, which is known for very few molecular ground states. We also discussed the O + Au2+ collision dynamics, which leads mostly to charge transfer to form Au+ and O+ species. This identification may help in identifying new routes for the reactivity of gold in the gas phase, in solution and in the condensed phase.

Using ab initio configuration interaction methodologies, we compute the potentials of the doubly and triply charged vanadium nitride. By performing benchmark calculations, we show that the 4s and 3d AOs are enough for the accurate description of VN multiple ionizations. In VN2+, several deep potential wells are located below the lowest dissociation limit. Within these potential wells, long-lived rovibrational levels may be found. Specifically, we find an unconventional shape for the ground state potential of VN2+ that differs from the volcanic form typical of dications. For VN3+, four shallow potential wells were characterized that may support rovibrational levels, where metastable VN3+ can be found. Accordingly, we predict the existence of VN2+ and VN3+ species in the gas phase as already noticed experimentally for the dication VN2+. For the bound states, we provide a set of accurate spectroscopic parameters. Double and triple ionization energies of VN are computed to be 23.56 and 51.05 eV, respectively.

We use accurate

We carried out a theoretical, fully

International audience; The magnetic exchange coupling between two diuranium(V) ions exhibiting the 5f1-5f1 configuration in diimide-bridged complexes [Cp3UV]2(μ-L) (L = stilbene-, naphthalene-diimide) has been investigated theoretically using relativistic ZORA/DFT calculations. Using two different hybrid PBE0 and B3LYP functionals, combined with the broken symmetry (BS) approach, we found that the BS states of both naphthalene and stilbene complexes have lower energy than the corresponding high-spin (HS) triplet ones. The B3LYP/BS estimated exchange coupling J constants (− 16.1 vs. − 9.0 cm−1 respectively for the naphthalene and stilbene complexes) corroborate well with those obtained previously for other pentavalent diuranium(V) diimide-bridged systems. The computed J value is found to be sensitive to π-network linking the two magnetic U(V) centers. The natural spin density distributions and molecular orbital analyses explain well the antiferromagnetic character of these compounds and clarify the crucial role of the π aromatic spacer in promoting spin polarization and delocalization favoring the magnetic coupling. Furthermore, the effective involvement of the 6d/5f metal orbitals in metal-ligand bonding plays an important role for the magnetic communication between the two active U(V) 5f electrons.

The spectra of helium-dominated white dwarf stars with hydrogen in their atmosphere present a distinctive broad feature centered around 1160~\AA\/ in the blue wing of the Lyman-$\alpha$ line. It is extremely apparent in WD 1425+540 recently observed with HST COS. With new theoretical line profiles based on ab initio atomic interaction potentials we show that this feature is a signature of a collision-induced satellite due to an asymptotically forbidden transition. This quasi-molecular spectral satellite is crucial to understanding the asymmetrical shape of Lyman-$\alpha$ seen in this and other white dwarf spectra. Our previous work predicting this absorption feature was limited by molecular potentials that were not adequate to follow the atomic interactions with spectroscopic precision to the asymptotic limit of large separation. A new set of potential energy curves and electronic dipole transition moments for the lowest electronic states of the H--He system were developed to account accurately for the behavior of the atomic interactions at all distances, from the chemical regime within 1~\AA\/ out to where the radiating H atoms are not significantly perturbed by their neighbors. We use a general unified theory of collision-broadened atomic spectral lines to describe a rigorous treatment of hydrogen Lyman-$\alpha$ with these potentials and present a new study of its broadening by radiative collisions of hydrogen and neutral helium. These results enable ab initio modeling of radiative transport in DBA white dwarf atmospheres., Comment: 9 pages, 7 figures

Sulfenyl thiocyanate compounds, RSSCN, are involved in the human immune system biochemical processes. They are also the routes for the synthesis of complex S-containing species such as polypeptides, or symmetrical (RSSR) and unsymmetrical disulfides (RSSR'). At present, we have characterized the stable forms of the simplest sulfenyl thiocyanate compound, HSSCN, at the coupled cluster level. We found twenty-three isomers, for which we determined a set of structural parameters, anharmonic frequencies and reaction energies for the formation of the corresponding diatomic + triatomic and atomic + tetratomic fragments. We also discussed the implications of the present findings for biological entities containing a disulfide bridge, where we identified three isomers that may serve as prototypes. Similarities and differences with other S/N hybrid bioactive molecules are also discussed. From an astrophysical point of view, we expect HSSCN isomers to be present in astrophysical media, since several of their molecular fragments have already been detected. In sum, the present set of data can be used for the identification of HSSCN compounds and understanding the physical chemistry of sulfur containing molecules in vivo, in the laboratory and in astrophysical media.

Recently, a series of carbazole derivatives containing chalcone analogues (CDCAs) were synthetized as potent anticancer agents and apoptosis inducers. These compounds target the inhibition of topoisomerase II and present cytotoxic activities. After comparison to experiment, we validated the use of B3LYP, a density functional theory-based approach, to describe the structure and molecular properties of the carbazole subunit and CDCAs compounds of interest. Then, we derived relationships between the chemical descriptors and activity of these carbazole derivatives using multi-parameter optimization and quantitative structure activity relationships (QSAR) approaches. For the QSAR studies, we used multiple linear regression and artificial neural network statistical modelling. Our predicted activities are in good agreement with the experimental ones. We found that the most important parameter influencing the activity of the considered compounds is the octanol-water partition coefficient, highlighting the importance of flexibility as a key molecular parameter to favor cell membrane crossing and enhance the action of these CDCAs against topoisomerase II. Our results provide useful guidelines for designing new oral active CDCAs medicaments for cytotoxic inhibition.

Although substantial advances have been made in a few reactions of industrial significance over single-atom catalysts (SACs), the origin of the superior catalytic performance, the nature of the active sites, and the reaction pathways are still the subject of debate. Even for CO oxidation over SACs on nonreducible substrates, the understanding is limited. We investigated the performance of Pd atoms monodispersed on graphene (PdGr) in CO oxidation. Combining first-principles-based thermodynamics calculations and microkinetics modeling, we showed that the positively charged PdGr can exhibit a rather high low-temperature activity in CO oxidation. Under reaction conditions, the Pd atom binds strongly with 02, acting as the reactive species to convert CO. A comparison of the conversion rates of steps along different potential reaction pathways provides direct evidence that CO oxidation mainly proceeds through revised Langmuir-Hinshelwood pathways, and the dissociation of the peroxide intermediate (O-O-C=O) is the rate limiting step. The predicted catalytic performance was attributed to the specific electronic structure of PdGr with the positively charged Pd on graphene monovacancy exposing sp-type frontier states. We expect these findings to help in understanding the performance of SACs and to guide the design and fabrication of SACs with superior catalytic performance.

We investigated the oxidation of formaldehyde, one of the major indoor air pollutants, into CO2 and H2O over Fe atoms trapped in defects on graphene by first-principles based calculations. These trapped Fe atoms are not only stable to withstand interferences with the reaction environments but are also efficient to catalyze the reactions between coadsorbed O2 and formaldehyde. The oxidation of formaldehyde starts with the formation of a peroxide-like intermediate and continues by its dissociation into a η1-OCHO coadsorbed with an OH radical. Then, the adsorbed OCHO undergoes conformational changes and hydride transfer, leading to the formation of H2O and CO2. Subsequent adsorption of O2 or formaldehyde facilitates desorption of H2O and a new reaction cycle initiates. The calculated barriers for formation and dissociation of the peroxide-like intermediate are 0.43 and 0.40 eV, respectively, and those for conformation changes and hydride transfer are 0.47 and 0.13 eV, respectively. These relatively low barriers along the reaction path suggest the potential high catalytic performance of these trapped Fe atoms for formaldehyde oxidation.

The unusual reactivity of organobismuth compounds in cross-coupling processes, where they act as multi-aryl sources, opens up new and exciting possibilities in the field of organic synthesis. In particular, the high reactivity of arylbismuths in multifold couplings with arylhalides suggests that three catalytic cycles occur simultaneously. Here, we carry out a computational investigation of a cross-coupling model reaction between bromobenzene (Ph-Br) and triphenylbismuthine (Ph3Bi), catalyzed by Pd(0). The energetic profile evidences the exergonic behavior of the overall reaction with a ΔrG of −38.2 kcal mol−1, in good agreement with the experimental results. Moreover, the largest activation energy (39.8 kcal mol−1) is found for the first Ph3Bi aryl transfer (PhP’1Ph1 → PhP’2Ph1), identified as the rate-determining step. Additional dynamical computations on these potential profiles are needed to confirm these findings. We expect this research to allow for a better understanding of organobismuth palladium-catalyzed CC coupling reactions and organobismuth chemistry in general.; The unusual reactivity of organobismuth compounds in cross-coupling processes, where they act as multi-aryl sources, opens up new and exciting possibilities in the field of organic synthesis. In particular, the high reactivity of arylbismuths in multifold couplings with arylhalides suggests that three catalytic cycles occur simultaneously. Here, we carry out a computational investigation of a cross-coupling model reaction between bromobenzene (Ph-Br) and triphenylbismuthine (Ph3Bi), catalyzed by Pd(0). The energetic profile evidences the exergonic behavior of the overall reaction with a Delta(r)G of -38.2 kcal mol(-1) , in good agreement with the experimental results. Moreover, the largest activation energy (39.8 kcal mol(-1)) is found for the first Ph3Bi aryl transfer ((P)(h)(P1)', (Ph1) -> (Ph)p(2)' (Ph1)), identified as the rate-determining step. Additional dynamical computations on these po-tential profiles are needed to confirm these findings. We expect this research to allow for a better understanding of organobismuth palladium-catalyzed C-C coupling reactions and organobismuth chemistry in general.

Potential energy curves (PECs) of the lowest electronic states of the potassium mono-sulphide KS have been determined with highly correlated ab initio calculations, using internally contracted multi reference interaction configuration methods including Davidson correction (MRCI + Q) with and without considering spin-orbit effects. For the three low-lying bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. An analysis of the properties of the three bound states, X2Π, 12Σ+ and 22Π, illustrates the common characteristics of the whole series of compounds in the MS family (M = Li, Na, K, Rb, Cs). Indeed, the shapes of the PECs of these bound states are strongly affected by the interactions between the two ionic states, 2Σ+ and 2Π, correlating at large internuclear separations (RMS) to the first ionic dissociation limit [M+ + S−] and the electronic states correlating to the three/four lowest dissociation limits. The spectroscopy of these low-lying electronic states and the lifetime of their vibrational levels are thus affected by the spin-orbit interactions which are mainly related to the S atom and consequently common to all alkali-metal mono-sulphides.

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We applied advanced ab initio treatments and large atomic basis sets to characterize the cesium oxide diatomic molecule (CsO) and its cation (CsO+) and anion (CsO−). We computed the electronic potential energy curves (PECs) of the low-energy states of these species along the internuclear distance to study their stability and spectroscopy. For these states, we computed vertical and adiabatic excitation energies and we found that those characterized as stable are mostly mono-configurational in nature. By solving the nuclear motion problem, we deduced a set of accurate spectroscopic data, including equilibrium geometries, harmonic vibrational frequencies, rotational constants, anharmonic vibrational constants, and the patterns of vibrational levels. Furthermore, we investigated the effect of the spin-orbit coupling on the electronic states correlating to the two lowest dissociation limits of the neutral molecule. We found that the PECs of these states are affected by the spin-orbit interaction. The adiabatic ionization energy of CsO is determined to be 6.52 eV. We compute also a relatively small adiabatic electronic affinity for CsO of 0.235 eV. Both values are in fair agreement with the experimental measurements. Our data may be used to identify CsO, CsO− and CsO+ in the laboratory or in oxygen- and cesium-rich media.

Quantitative structure-activity relationship (QSAR) models are useful tools for understanding the relation between biological activity and chemical structure, and for the design of new drugs. In this work, the performances of two QSAR approaches for modelling and predicting glutathione-S-transferases (GSTP1-1) inhibition are compared, namely Multiple Linear Regression (MLR) and Artificial Neural Network (ANN). These models are applied to 38 thiol substituted nitrobenzoxadiazole inhibitors. For these compounds, we found that the nonlinear model performs better than the linear one in terms of predictive ability, indicating a non-linear relation between the selected molecular descriptors and GSTP1-1 inhibition. The validity of the proposed models was established using the following techniques: separation of data into independent training and test sets, leave-one-out cross-validation, and Y-randomization. Otherwise, the domain of applicability indicating the area of reliable predictions was defined. Through the adopted QSAR model and in silico virtual screening, we identified 23 hits with good predictability. Our work should motivate future in vitro investigations on these compounds.

The ethynyl cation, C2H+, is of great importance in astrophysical media and in combustion. It is involved in the formation of larger organic compounds and in their decomposition mechanisms. Here, we investigate the low-lying electronic states of this cation using pure ab initio methodologies. The evolution of its potential energy surfaces along the stretching and bending coordinates reveals a high density of electronic states that favours mutual interactions and the mixing of wavefunctions. The ground state is of 3Π space symmetry and the lowest singlet state (1Π) is found to be a quasi-linear-quasi-linear Renner-Teller system. Our work suggests that the (spin-)rovibronic spectrum of such a molecular system is complicated, because of the contributions of multiple couplings, including Renner-Teller, vibronic and spin-orbit. We also deduced the adiabatic ionization energy of the ethynyl radical, in good agreement with recent measurements. In summary, our work shows that the ethynyl cation, in spite of its small size, still represents a challenging molecular problem to be solved.

International audience; Using multi configurational ab initio methodologies, we compute the potential energy curves (PECs) of the lowest electronic states of the diatomic CsS. These computations are performed using internally contracted multi reference interaction configuration including Davidson correction (MRCI+Q) with and without considering spin-orbit effects. The shapes of the PECs are governed by the interactions between the two ionic states, 2+ and 2, correlating at large internuclear separations (RCsS) to the first ionic dissociation limit and the other electronic states correlating to the three lowest neutral dissociation limits. Computations show the importance of considering large amount of electron correlation for the accurate description of the PECs and spectroscopy of this molecular system. As expected, these PECs are also strongly affected by the spin-orbit interaction. For the bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. Moreover, we show that the 22 state presents a “bowl” potential with a rather flat region extending to large RCsS distances. After being promoted to this state, wavepackets should undergo strong oscillations, similar to those observed by Zewail and co-workers for the NaI molecule. These should provide information on the shape of the PEC for the 22 state and also on the couplings between this and the neighbouring states.

We present a first-principles systematic study on the bonding and structure of the complexes between zinc(II) chloride and tributylphosphine chalcogenides, n-Bu3PE (E = O, S, Se). These investigations are carried out within the framework of the density functional theory with and without considering the dispersion corrections evaluated at the GD3 level. Inspection of the calculated binding energies, orbitals, charge transfers and natural bond orbital analysis shows the importance of the interplay between σ- and π-type bonding within P–E and E–Zn in the formation of these complexes. Calculations reveal that the P–E–Zn angle goes from 120° to 90° when going from O to Se. In the complexes, the P–E bonds resemble those in the isolated PE− diatomic anions, where an electron density excess is found on the chalcogen E whatever its nature. A bonding model for this type of organometallic complexes is proposed and discussed here for the first time.

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A set of accurate spectroscopic parameters for the detection of the atmospherically important HOC(O)O radical has been obtained by means of state-of-the-art ab initio computations. These include advanced coupled cluster treatments, involving both standard and explicitly correlated approaches, to correctly account for basis set incompleteness and core-valence effects. Geometric parameters for the X∼2A′ and Ã2A′′ states and, for the ground state only, vibrationally corrected rotational constants including quartic and sextic centrifugal distortion terms are reported. The infrared spectrum of the X∼2A′ state has been simulated in the 4000-400 cm-1wavenumber interval with an approach based on second order vibrational perturbation theory that allows accounting for anharmonic effects in both energies and intensities. Finally, the vibronic spectrum for the à ← X∼ transition has been calculated at three different temperatures in the 9000-3000 cm-1energy range with a time-independent technique based on the Franck-Condon approximation.

The hydroxymethyl peroxy (HMOO) radical is a product of the oxidation of non-methane hydrocarbons. The present study provides the first accurate computational determination of critical spectroscopic features of the title radical that should aid in its experimental characterization. Structure, energetics, vibrational frequencies, and rotational parameters are reported for the three stable isomers on the ground electronic state of HMOO. While preliminary computations have been carried out using density functional theory as well as second-order Møller-Plesset perturbation theory, for the accurate structural and spectroscopic characterization we made use of coupled-cluster techniques, herewith considering both standard and explicitly correlated methods. The "CCSD(T)/CBS + CV" composite scheme, a state-of-the-art composite approach based on the coupled-cluster theory including single and double excitations together with a perturbative treatment of triples that accounts for extrapolation to the complete basis-set limit as well as core-valence correlation effects, is used to obtain accurate structural and energetic data, in particular for the decomposition reaction to HO

The simplest N-sulfonylamine HNSO2 has been generated in the gas phase through flash vacuum pyrolysis of methoxysulfonyl azide CH3OS(O)2N3. Its identification was accomplished by combining matrix-isolation IR spectroscopy and quantum chemical calculations. Both experimental and theoretical evidence suggest a stepwise decomposition of the azide via the methoxysulfonyl nitrene CH3OS(O)2N, observed in the 193 nm laser photolysis of the azide, with concerted fragmentation into CH2O and HNSO2. Upon the 193 nm laser irradiation, HNSO2 isomerizes into the novel N-hydroxysulfinylamine HONSO.

The simplest N-sulfonylamine HNSO2 has been generated in the gas phase through flash vacuum pyrolysis of methoxysulfonyl azide CH3OS(O)2N3. Its identification was accomplished by combining matrix-isolation IR spectroscopy and quantum chemical calculations. Both experimental and theoretical evidence suggest a stepwise decomposition of the azide via the methoxysulfonyl nitrene CH3OS(O)2N, observed in the 193 nm laser photolysis of the azide, with concerted fragmentation into CH2O and HNSO2. Upon the 193 nm laser irradiation, HNSO2 isomerizes into the novel N-hydroxysulfinylamine HONSO.

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A first principle study of the cross-coupling reaction between 3-chloro-6-iodopyridazine and triphenylbismuth under palladium catalysis has been carried out. The approach selected for this investigation is the density functional theory within the framework of the PBE0 and B3LYP hybrid exchange–correlation functionals, with and without including empirical corrections for the dispersion forces at the GD3 level. For this reaction, a three-step mechanism including an oxidative addition, a transmetalation and a reductive elimination has been proposed. All intermediates and transition states have been fully characterized. The energy profile is deduced in gas phase and in solvent. Calculations suggest that the oxidative addition is the rate-determining step for the entire cross-coupling reaction.

Small methane clusters (CH4)n are irradiated using intense femtosecond laser excitation at 624 nm. The ionized species and those resulting from their fragmentation are detected via time-of-flight mass spectrometry (TOF MS). We find evidence of bound, multiply charged methane molecules and clusters resulting from Coulomb explosion upon exposure to highly energetic, ultrafast radiation. The assignment of the mass spectra is done after first-principles calculations (at the (R)MP2/aug-cc-pVXZ (X = D,T) level) on the charged (CH4)n(q+) clusters (n = 1-4, q = 1-4). We also considered the cluster stabilities and fragments that may result from intracluster molecular reactivity. Complex intracluster ion-molecule reactions induced by photoionization are expected to occur. Interestingly, we show that multi charged small methane clusters undergo intracluster reactions and fragmentations which are different from those observed for isolated methane ions or for large ionized methane clusters.

The HOC(O)O radical is a product of the reaction of HOCO radicals with oxygen atoms. The present study provides theoretical prediction of critical spectroscopic features of this radical that should aid in its experimental characterization. Energies, structures, rotational constants, and harmonic frequencies are presented for the ground and two low-lying excited electronic states of HOC(O)O. The energies for the A ∼ 2 A ″ → X ∼ 2 A ′ and B ∼ 2 A ′ → X ∼ 2 A ′ electronic transitions are reported. The band origin of the B ∼ → X ∼ transition of HOC(O)O is predicted to occur in the near infrared region of the spectrum at around 1.5 eV and it is suggested to be the most promising one for observing this radical spectroscopically. The structural and spectroscopic similarities between HOC(O)O and the isoelectronic radical FC(O)O are discussed. The abundance of experimental data on the FC(O)O radical should guide the spectroscopic characterization of HOC(O)O and serve as a benchmark for the structural and spectroscopic parameters obtained from theory.

We investigate VO2+ and VO3+ ions theoretically. The electronic computations are performed using multi reference configuration interaction approaches in conjunction with the aug-cc-pV5Z basis set. VO2+ potential possesses a Morse-like shape instead of the common volcanic shape since both the charge retaining (V2+ + O) and charge separating (V+ + O+) dissociation channels are almost coinciding in energy. Its intense blue color is due to the A2Π–X2Δ transition. We predict VO3+ as metastable. For bound states, we derived a set of accurate spectroscopic parameters. We estimate the adiabatic double and triple ionization energies of VO to be 22.5 eV and 50.9 eV.

At present, we investigate the mechanisms for bismuth-catalyzed direct benzylation of 2,4-pentanediones using various density functional theories and post-Hartree–Fock ab initio methods. First, we deeply consider the role of BiCl3, where six scenarios are proposed. All of them start with the formation of a weakly bound complex between the BiCl3 catalyst and the alcohol or the dione. The most favorable one corresponds to the direct access to the products via a unique transition state (SN2-type mechanism). We also examined the effects of various nonpolar and polar solvents, which are viewed to slightly affect the energy profiles for SN2 and internal nucleophilic substitution (SNi) types of mechanism, whereas strong perturbations are observed for SN1 mechanism. For instance, the later one becomes the most thermodynamically favorable in DMSO solvent. In addition, several classes of benzyl alcohols and catalysts (BiX3, where X = Cl, Br, I, NO3, and OTf) were considered within the framework of SN2 and SNi mechanisms. The reactivity of these alcohols increases going from primary to secondary to tertiary. These findings are in line with the present available experimental results. Finally, our computations suggest that Bi(NO3)3 could be an excellent catalyst for the title reaction.

In an effort to provide an accurate structural and spectroscopic characterization of acetyl cyanide, its two enolic isomers and the corresponding cationic species, state-of-the-art computational methods, and approaches have been employed. The coupled-cluster theory including single and double excitations together with a perturbative treatment of triples has been used as starting point in composite schemes accounting for extrapolation to the complete basis-set limit as well as core-valence correlation effects to determine highly accurate molecular structures, fundamental vibrational frequencies, and rotational parameters. The available experimental data for acetyl cyanide allowed us to assess the reliability of our computations: structural, energetic, and spectroscopic properties have been obtained with an overall accuracy of about, or better than, 0.001 Å, 2 kcal/mol, 1-10 MHz, and 11 cm(-1) for bond distances, adiabatic ionization potentials, rotational constants, and fundamental vibrational frequencies, respectively. We are therefore confident that the highly accurate spectroscopic data provided herein can be useful for guiding future experimental investigations and/or astronomical observations.

We investigate the importance of orbital localization in the application of the Density Matrix Renormalization Group (DMRG) technique to ab initio studies of molecular electronic structure. Our previous implementation of DMRG has been generalized to allow for the use of localized nonorthogonal orbitals. Simple cycles of equidistant hydrogen atoms, which are good examples of one dimensional metal-like lattices with fully delocalized electronic structures, have been taken as test models. In this study, the efficiency of the DMRG method and the importance of orbital localization for the generation of the DMRG building blocks are confirmed. However, it is found that the convergence of the procedure based on nonorthogonal orbitals is slower and requires more DMRG components than the standard orthogonal formulation. Symmetrically orthonormalized atomic orbitals are shown to be a good compromise solution: they satisfy the requirement of orbital localization for the generation of the DMRG blocks and improve the convergence, reducing the number of components of the DMRG expansion. (c) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

The stable low energy states of the HPS and DPS molecules have been studied through multi-reference ab initio methods in conjunction with large atomic basis sets. Stable states for these species have been examined up to 7 eV above the ground state minimum. We found six stable electronic states that are mostly mono-configurational. These states may be involved in the photodynamics and photodissociation of this molecule. In particular, the 2 1A' state presents two minima on the potential energy surface, one of them close to linear configuration. This state may be populated after the absorption of a visible photon from the ground state and gives rise to large amplitude motions that may eventually induce isomerization to electronically excited HSP. Moreover, we characterized these states spectroscopically to facilitate the assignment of the vibronic spectra of the HPS and DPS species. For these low-energy states, we thus computed vertical and adiabatic excitation energies, and for the stable ones, a full set of spectroscopic constants including harmonic frequencies and anharmonic vibrational, rotational, and centrifugal distortion constants. The calculated potential energy surfaces for these states have been used in a variational procedure to deduce the pattern of vibrational levels up to 4000 cm-1 above the corresponding vibrationless level. Our data may serve for the assignment of the IR and Vis spectra of HPS and DPS.

Using augmented sextuple zeta basis sets and internally contracted multireference configuration interaction (MRCI) wavefunctions, potential energy, electric dipole and transition moments have been computed for the X3Π, a1Σ+, b1Π and A3Σ− states of BP, X2Σ+ and A2Π states of BP− and X4Σ− and A4Π states of BP+. From these data spectroscopic constants, radiative transition probabilities and photoelectron spectra of BP− and BP have been evaluated. The non-vanishing spin–orbit coupling elements between the four low lying triplet and singlet states of the neutral BP have also been calculated from MRCI wavefunctions. The treatment of the corresponding perturbations in the manifold of dense rovibrational states in the three lowest states would require a precise knowledge of the electronic excitation energies. Our best singlet–triplet separations (X–a) are calculated to be 2412 cm−1 (MRCI) and 2482 cm−1 (restricted coupled cluster with perturbative triples (RCCSD(T))) with an estimated error bound of about ±200 cm−1. All three states have long radiative lifetimes with cascading among the rovibrational levels of different states. The ionization energy IEe of BP is calculated to be 9.22 eV (MRCI) and 9.48 eV (RCCSD(T)), the electron affinity EAe 2.51 eV (MRCI) and 2.74 eV (RCCSD(T)). The photoelectron spectra of BP and BP− have been obtained from the Franck–Condon factors of the MRCI potentials. For the UV spectroscopy the dipole allowed radiative transition probabilities are given for A3Σ− ↔ X3Π, b1Π ↔ a1Σ+ of BP, A2Π ↔ X2Σ+ of BP− and A4Π ↔ X4Σ− of BP+. The ionization energy IEe of B2P2 of 8.71 eV and the electron affinity EAe of 2.34 eV have been calculated by the RCCSD(T)/aVQZ approach. Also the harmonic vibrational wavenumbers for the electronic ground states of the ions B 2 P 2 + and B 2 P 2 - are given.

For three energetically most stable structures of tetrasulfur, S4, S4+ and S4- (cis-chain, rectangular, and trans-chain forms), equilibrium geometries, harmonic wavenumbers, ionization energies, electron affinities, electronic vertical and adiabatic excitation energies, and electronic transition moments were calculated by ab initio methods. It was found that similarly to the ground state of S4, the S4+ cis-isomer could interconvert, perturbed, however, by vibronic coupling with a very close-lying excited state and large-amplitude vibrations. Moreover, the cis- and rectangular minima are calculated to be energetically degenerated. The ω values in all three species agree reasonably well with existing experimental and theoretical data. The calculated patterns of harmonic modes suggest the existence of very complex low-lying anharmonic polyads in all three species. The calculated ionization energies reported previously are compared with the present more accurate data. Also the electronic transition moments and the energy positions of the electronic states with higher spin multiplicities are given.

Results are presented that suggest that thiazyl hydride (HSN)/thionitrosyl hydride (sulfimide, HNS) can be used as light-sensitive compounds for NO-delivery in biological media, as well as markers for the possible detection of intermediates in nitrites + H2S reactions at the cellular level. They are expected to be more efficient than the HNO/HON isovalent species and hence they should be considered instead. A set of characteristic spectroscopic features are identified that could aid in the possible detection of these species in the gas phase or in biological environments. The possibility of intramolecular dynamical processes involving excited states that are capable of interconverting HNS and its isomeric form HSN is examined.

Studying the interaction of molecular nitrogen with extreme ultraviolet (XUV) radiation is of prime importance to understand radiation-induced processes occurring in Earth’s upper atmosphere. In particular, photoinduced dissociation dynamics involving excited states of N2+ leads to N and N+ atomic species that are relevant in atmospheric photochemical processes. However, tracking the relaxation dynamics of highly excited states of N2+ is difficult to achieve, and its theoretical modeling is notoriously complex. Here, we report on an experimental and theoretical investigation of the dissociation dynamics of N2+ induced by isolated attosecond XUV pulses in combination with few-optical-cycle near-infrared/visible (NIR/VIS) pulses. The momentum distribution of the produced N+ fragments is measured as a function of pump-probe delay with subfemtosecond resolution using a velocity map imaging spectrometer. The time-dependent measurements reveal the presence of NIR/VIS-induced transitions between N2+ states together with an interference pattern that carries the signature of the potential energy curves activated by the XUV pulse. We show that the subfemtosecond characterization of the interference pattern is essential for a semiquantitative determination of the repulsive part of these curves, We acknowledge support from the European ResearchCouncil under ERC Grants No. 637756 STARLIGHT, No. 227355 ELYCHE, and No. 290853 XCHEM, from LASERLAB-EUROPE (Grant Agreement No. 284464,EC’s Seventh Framework Programme), from European COST Action CM1204 XLIC, the MICINN ProjectFIS2013-42002-R, the ERA-Chemistry Project PIM2010EEC-00751, the European Grant MC-ITNCORINF. Calculations were performed at the Centro deComputación of the Universidad Autónoma de Madrid(CC-UAM) and the Barcelona Supercomputing Center(BSC). G. S. acknowledges the Italian Ministry of Research Project FIRB No. RBID08CRXK. R. L. and M. H. acknowledge a Marie Curie International Research Staff Exchange Scheme Fellowship (Grant AgreementNo. PIRSES-GA-2012-31754, EC’s Seventh Framework Programme) and the COST Action CM1405 MOLIM.C. L. acknowledges National Natural Science Foundationof China (Grants No. 11127901, No. 61221064, andNo. 11404356), 973 Project (Grant No. 2011CB808103)..

We wish to understand the processes underlying the ionization dynamics of N2 as experimentally induced and studied by recording the kinetic energy release (KER) in a XUV-pump/IR-probe setup. To this end a theoretical model was developed describing the ionization process using Dyson Orbitals and, subsequently, the dissociation process using a large set of diabatic potential energy surfaces (PES) on which to propagate. From said set of PES, a small subset is extracted allowing for the identification of one and two photon processes chiefly responsible for the experimentally observed features We acknowledge support from the European Research Council under ERC Grants No. 637756 STARLIGHT, No. 227355 ELYCHE, and No. 290853 XCHEM, from LASERLAB-EUROPE (Grant Agreement No. 284464, EC’s Seventh Framework Programme), from European COST Action CM1204 XLIC, the MICINN Project FIS2013-42002-R, the ERA-Chemistry Project PIM2010EEC-00751, the European Grant MC-ITN CORINF. Calculations were performed at the Centro de Computación of the Universidad Autónoma de Madrid (CC-UAM) and the Barcelona Supercomputing Center (BSC). G. S. acknowledges the Italian Ministry of Research Project FIRB No. RBID08CRXK. R. L. and M. H. acknowledge a Marie Curie International Research Staff Exchange Scheme Fellowship (Grant Agreement No. PIRSES-GA-2012-31754, EC’s Seventh Framework Programme) and the COST Action CM1405 MOLIM. C. L. acknowledges National Natural Science Foundation of China (Grants No. 11127901, No. 61221064, and No. 11404356), 973 Project (Grant No. 2011CB808103). We are very grateful to Alicia Palacios for fruitful discussions on the ionization model

First-principle full valence complete active space calculations (CASSCF) are reported for the electronic states of the D2 h and C2 v planar isomers of B4, B4 + and B4 −. This approach is found to reproduce well the experimentally known transition energies for the two lowest excited triplet states of the most stable rhombic B4 isomer. The pattern of electronic transitions up to about 4.5 eV for B4 singlet and B4 + doublet states calculated in similar way should guide an UV spectroscopic search.

The present theoretical calculations on CP X2Σ+, A2Π, 14Σ+, 14Δ, 14Π, 16Π and 16Σ+ electronic states use standard and explicitly correlated coupled cluster approaches, multi-reference configuration interaction (MRCI) techniques in connection with a large panel of basis sets. We also examined core–valence (CV) and scalar relativistic (SR) effects. For the ground electronic state, our calculations reveal that the MRCI+CV+SR method and the coupled cluster technique with perturbative treatment of triple excitations including scalar relativistic effects computed with the Douglas-Kroll approach (RCCSD[T]-DK) in connection with a large basis set lead to an accurate description of CP(X2Σ+). We computed the evolution along the internuclear distance of the diagonal and the off-diagonal spin–orbit integrals between the X2Σ+ and A2Π states. These integrals are then incorporated together with the corresponding potentials into variational treatment of the nuclear motion. We deduced hence the energy positions of the low...

Due to strong electron correlation effects and electron coupling with nuclear motion, the molecular inner-valence photoionization is still a challenge in electron spectroscopy, resulting in several interesting phenomena such as drastic changes of angular dependencies, spin-orbit induced predissociation, and complex interplay between adiabatic and nonadiabatic transitions. We investigated the excited electronic states of HCl(+) in the binding energy range 27.5-30.5 eV using synchrotron radiation based high-resolution inner-valence photoelectron spectroscopy with angular resolution and interpreted the observations with the help of ab initio calculations. Overlapping electronic states in this region were disentangled through the analysis of photoelectron emission anisotropies. For instance, a puzzling transition, which does not seem to obey either an adiabatic or a nonadiabatic picture, has been identified at ∼28.6 eV binding energy. By this study, we show that ultrahigh-resolution photoelectron spectroscopy with angular selectivity represents a powerful tool to probe the highly excited ionic molecular electronic states and their intricate couplings.

We performed accurate ab initio investigations of the geometric parameters and the vibrational structure of neutral HNS/HSN triatomics and their singly charged anions and cations. We used standard and explicitly correlated coupled cluster approaches in connection with large basis sets. At the highest levels of description, we show that results nicely approach those obtained at the complete basis set limit. Moreover, we generated the three-dimensional potential energy surfaces (3D PESs) for these molecular entities at the coupled cluster level with singles and doubles and a perturbative treatment of triple excitations, along with a basis set of augmented quintuple-zeta quality (aug-cc-pV5Z). A full set of spectroscopic constants are deduced from these potentials by applying perturbation theory. In addition, these 3D PESs are incorporated into variational treatment of the nuclear motions. The pattern of the lowest vibrational levels and corresponding wavefunctions, up to around 4000 cm(-1) above the corresponding potential energy minimum, is presented for the first time.