Search

We aim to hunt for massive binaries hosting a black hole companion (OB+BH) and establish the natal mass-ratio distribution of massive stars at the subsolar metallicity environment of the Large Magellanic Cloud (LMC). We use the shift-and-add grid disentangling technique to characterize the hidden companions in 51 SB1 O-type and evolved B-type binaries in the LMC monitored in the framework of the Tarantula Massive Binary Monitoring (TMBM). Out of the 51 SB1 systems, 43 (84%) are found to have non-degenerate stellar companions, of which 28 are confident detections, and 15 are less certain (SB1: or SB2:). Of these 43 targets, one is found to be a triple (VFTS 64), and two are found to be quadruples (VFTS 120, 702). The remaining eight targets (16%) retain an SB1 classification. Aside from the unambiguous case of VFTS 243, analysed in detailed in a separate paper, we identify two additional OB+BH candidates: VFTS 514 and VFTS 779. Additional black holes may be present in the sample but at a lower probability. Our study firmly establishes a virtually flat natal mass-ratio distribution for O-type stars at LMC metallicity, covering the entire mass-ratio range (0.05 < q < 1) and periods in the range 0 < log P < 3 [d]. The nature of the OB+BH candidates should be verified through future monitoring, but the frequency of OB+BH candidates is generally in line with recent predictions at LMC metallicity., 41 pages (14 main article + 27 appendix), accepted to A&A

The N-(4-nitrophenyl)methacrylamide homopolymer (poly(4NPMA)) and copolymer of limonene with N-(4-nitrophenyl)methacrylamide (4NPMA-co-LIM) have been synthesized and characterized by FT-IR and NMR spectroscopic methods. The spectroscopic properties of poly(4NPMA) and 4NPMA-co-LIM were predicted using Density Functional Theory (DFT) calculations. The results have been compared with observed values, and they match with each other. Frontier orbital analysis (FMOs), global reactivity descriptors, MEP as well as Mulliken atomic charge were calculated with same method for poly(4NPMA) and 4NPMA-co-LIM. The physical properties of homopolymer of NPMA and its copolymer with D-Limonene were compared and evaluated. Thermal stabilities of homo and copolymer were investigated.

A localized bond orbital analysis of the bonding in dioxygen and related species provides a unique fundamental insight into its bonding characteristics. It reveals the coalescence of the molecular orbital and valence bond/Lewis approaches and clearly demonstrates that the often stated inability of valence bond theory to describe the bonding of O2 is a myth. The analysis indicates that the σ-bond strength of 3O2 is not weak as previously believed and accounts for much of its enhanced stability compared with hydroperoxyl. We attribute the stability and persistence of 3O2 to a combination of this attribute and favorable maximization of exchange coupling between the valence electrons.

This paper proposes a new form of stray flux sensor, placed on the inner side of the machine rear end plate, in order to monitor the presence and evolution of some most common faults in three-phase induction motors. The fault indicator is based on analysis of orbits built from time flux signals collected by the sensor. The effectiveness of this methodology was checked considering three types of faults under three different load conditions: incipient inter-turn short circuits, unbalanced voltage supplies and misalignment, all with 0%, 50% and 100% loads. The experimental results showed a viability of the technique for diagnosing and monitoring of induction motors. This can be adapted and used in predictive maintenance in industry.

The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long-term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round-trip journey. The L4 mission concept is technically feasible, and is scientifically compelling. ISSN:1542-7390

This study investigates the effect of different substituents on the interactions between Fe(CO)4 and substituted benzynes (C6X4, X = H, F, Cl, Br, CN, Me) in Fe(CO)4(η2-C6X4) complexes using MPW1PW91-based quantum mechanical calculations. In this respect, the study eva­luates the influence of electron withdrawing and donating groups on the Fe—Cbenzyne bond distances and topological properties. In addition, the frontier orbital analysis is used to illustrate the electronic structure of complexes, and the percentage composition in terms of the defined groups of frontier orbitals is evaluated. To obtain insights into the physical nature of Fe—Cbenzyne bonds, we extensively use the energy decomposition analysis (EDA) and Bader's Quantum Theory of Atoms-in-Molecules (QTAIM). To this end, in addition to the examination of the properties of bond critical points, we apply the Pendas interacting quantum atoms (IQA) scheme, which enables a rigorous and physical study of Fe—Cbenzyne bonds in these complexes. Also, electron localization function (ELF) and localized-orbital locator (LOL) calculations are used to illustrate Fe—C bonds in the investigated complexes.

The first isolable Ge5-spiropentadiene 1 was synthesized via the reduction of (iPr3Si)2NGeCl (3) with potassium. The crystal structure of 1 reveals a spirocyclic Ge5 skeleton containing two Ge-Ge double bonds (avg. 2.34 A), which are fettered in two Ge3 rings with a dihedral angle of 70.193°. The DFT calculations and orbital analysis show that the σ-delocalization of the Ge5 skeleton and the 2π-delocalized aromatic Ge3 rings enhance the stability of molecule 1.

Main group cluster compounds have attracted increasing attention in the past decades. Despite recent developments in their synthesis, the description of their electronic structures is usually limited to simply applying Wade's rule originally developed for borane compounds. This traditional approach is once again challenged by two recently reported group 14 metalloid clusters in the form of [Pd3Ge18R6]2-. In this work, we put forward a modular bonding model for these two clusters, via principal interacting orbital (PIO) analysis. The site preference for six substituents has also been analyzed.

ispartof: ASTRONOMY & ASTROPHYSICS vol:650 status: published

Dinitrogen activation in non-metallic systems has received considerable attention in recent years. Herein, we report the theoretical feasibility of N2 fixation using aminocarbenes (L) or their anionic derivatives. The molecular descriptors of L and anionic L‾, which affect the interaction of L and anionic L‾ with N2, were identified through multiple linear regression analysis. Additionally, the electron flow during C‒N bond formation was confirmed by performing intrinsic reaction coordination calculations with intrinsic bond orbital analysis for the reaction of anionic L‾ with N2.

Photoswitch triads comprising two dihydroazulene (DHA) units in conjugation with a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and para-disubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. In contrast, for the meta-connected triad, all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. Ultrafast spectroscopy of the photoisomerizations revealed a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversion with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computation (excitation spectra and orbital analysis of the transitions).

Magnetic response properties of 1,2,3,5-tetrazine derivatives including the newly synthesized 4,6-diphenyl-1,2,3,5-tetrazine have been studied computationally at the density functional theory (DFT) level. Calculations of magnetically induced current densities and induced magnetic fields show that the unsubstituted 1,2,3,5-tetrazine is almost as aromatic as benzene. Separating the magnetic shielding functions into molecular orbital components provided additional insights into the magnetic response. The aromatic character estimated from magnetically induced current densities and induced magnetic fields shows that NICS pi zz(0) values and ring-current strengths yield about the same degree of aromaticity, whereas NICSzz(0) and NICSzz(1) values are contaminated by sigma electron contributions. The studied 1,2,3,5-tetrazine derivatives are less aromatic than the unsubstituted one. Calculations of magnetic response properties of 4,6-diphenyl-1,2,3,5-tetrazine showed that it is the least aromatic among the studied molecules according to the ring-current criterion, while 4,6-[1,2,3,5]-ditetrazinyl-1,2,3,5-tetrazine is as aromatic as 4,6-dimethyl-1,2,3,5-tetrazine and slightly less aromatic than the unsubstituted 1,2,3,5-tetrazine.

A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [AI][CrMII(HCO2)6] (AI = NH4H2OI and M = Mn for 1, AI = CH3NH3I and M = Fe for 2, AI = CH3NH2CH3I and M = Co for 3, AI = CH3NH3I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of CrIII (t2g3eg) and MII (t2g3eg2 for MnII, t2g4eg2 for FeII, t2g5eg2 for CoII, t2g6eg2 for NiII) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1–4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between CrIII and MnII ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (−ΔSmmax) up to 43.9 J kg–1 K–1 with ΔH = 7 T and T = 3.5 K, lar...

A solar magnetic sailing spacecraft utilizes the interaction between solar wind and magnetic field that is generated by a loop of superconducting wire attached onboard of the spacecraft. The development of the working principle of solar magnetic sailing from MagSail to magnetospheric plasma propulsion and magneto-plasma-sail is reviewed and discussed to study their performance, focusing on its operation for interplanetary travel. The orbital dynamic of MagSail is elaborated to explore the probable trajectories of interest for space travel. Examples for MagSail interplanetary travel are discussed for insight and future continuing work.

This study was conducted to investigate the effect of various substituents on the Cr=C bond in the [(OC)5Cr=C(OEt)-para-C6H4X] complexes using B3LYP*-based quantum mechanical calculations. In this respect, the study evaluates the influence of electron withdrawing and donating groups on the Cr=C bond distances and topological properties and correlates the calculated parameters with the Hammett and Brown constants for the para-substituted (σp and σ p + , respectively) functional groups. Also, the frontier orbital analysis was used to show the electronic structure of complexes and the percentage composition in terms of the defined groups of frontier orbitals was evaluated. To obtain insight into the physical nature of Cr=C bond bonds, we extensively used energy decomposition analysis and Bader’s Quantum Theory of Atoms-in-Molecules (QTAIM). With this aim, in addition to examining the bond critical points properties, we apply Pendas’ Interacting Quantum Atoms (IQA) scheme, which enables the rigorous and physical study of Cr=C bonds in these complexes.

The gas phase proton transfer process in 1,2,4-triazolium dinitramide (TD) was studied using second-order perturbation theory to determine how the presence of one and two water molecules modifies the potential energy surface that connects the ion pair to the neutral pair. The presence of one water molecule can introduce small proton transfer energy barriers that separate the ion pair from the lower-energy neutral pair. These energy barriers are easily surmounted. Reaction paths were determined for single proton transfers and double proton transfers via one water molecule. In the presence of two water molecules, the global minimum is an ion pair, as are most of the lower-energy local minima. Energy barriers for single, double, and triple proton transfers were also found for TD in the presence of two water molecules. One TD ion pair structure with two water molecules has no corresponding neutral pair energy minimum. A quasi-atomic orbital analysis is used to understand the nature of the bonding in the various species studied in this work.

A detailed analysis of the C(sp3)−H activation process by vinylidene AuI complexes is described based on an intrinsic bond orbital analysis. Based on our analysis this event can be divided into three phases: (i) hydride transfer, (ii) C−C bond formation, and (iii) σ to π rearrangement of the lone pair coordinated to Au. Small perturbations of the system lead to either a concerted asynchronous reaction, or a stepwise reaction featuring an intermediate with a C-H-C three-centre two-electron (3c–2e) bond. The role of π-donating substituents is highlighted and provides a way of controlling reactions of this type in future experimental studies.

In this study, we report the substituent effect on the structures, frontier orbital analysis, and spectroscopic properties (IR, 13C, 29Si NMR) in the molybdenum silylidyne complexes CpMo(CO)2(≡Si-para-C6H4X) (X = H, F, Cl, CN, NO2 , Me, OMe, NH2 , NHMe) using MPW1PW91 quantum chemical calculations. The calculated structural parameters and spectral parameters are compatible with the experimental values in similar complexes. The nature of the chemical bond between the [Cp(OC) 2Mo]− and [Si-para-C6H4X]+ fragments was explored with energy decomposition analysis (EDA). The percentage composition in terms of the defined groups of frontier orbitals for CpMo(CO)2(≡Si-para-C6H4X) complexes was investigated to explore the character of the metal–ligand bonds. The linear correlations between the properties and Hammett constants (σ p) were illustrated. Natural bond orbital analysis (NBO) was used to illustrate the electronic structure of the complexes.

Московского государственного университета им. М.В. Ломоносова, Москва, Россия В данной статье рассматриваются различные технически реализуемые сценарии выведения малых спутников на орбиты для изучения радиационных поясов Земли. Рассчитываются параметры сценариев попутного запуска малого спутника ракетой среднего класса и кластерного запуска двух малых спутников ракетой легкого класса на эллиптические орбиты. Показана реализуемость попутного выведения малых спутников и выведения кластера из двух малых ИСЗ на орбиты с учётом желаемых параметров их взаимного расположения с помощью носителей среднего и легкого класса. Рассматривается переход между заданными орбитами в импульсной постановке с учетом второй зональной гармоники J2., In this paper, different scenarios of technically realizable schemes of launch of the small satellites for the monitoring of Earth radiation belts are considered. Parameters of the accompanied launch of small satellite by medium-class rocket and the launch of a cluster of two small satellites by a light-class rocket to the elliptical orbits are calculated. Technical feasibility of the mission requirements shown on the basic of calculated trajectory schemes. The orbit propagation is performed considering the central gravity of the Earth and second zonal harmonics J2, two-impulse maneuvers are considered and calculated to change the orbital parameters in order to transfer between given orbits., Bu məqalədə, Yerin radiasiya qurşaqlarının öyrənilməsi məqsədilə kiçik peyk qruplaşmasının orbitlərə çıxarılmasının müxtəlif texniki mümkün olan sxemləri nəzərdən keçirilir. Kiçik peykin orta sinif daşıyıcı və kiçik peyk qruplaşmasının yüngül sinif daşıyıcı vasitəsilə elliptik orbitlərə buraxılmasının parametrləri ölçülür. Kiçik peyklərin yüngül və orta sinif daşıyıcılar vasitəsilə fərqli elliptik orbitlərə buraxılmasının və eyni orbitdə fərqli fazalara ayrılmasının parametrləri ölçülərək, nəzərdən keçirilən ssenarilərin texniki mümkünlüyü göstərilmişdir. Peyklərin orbitə buraxılması Yerin mərkəzi cazibə güvvəsi və J2 ikinci zonal harmonikanın təsiri altında, orbitlərin parametrlərinin iki impulslu manevrlər vasitəsilə dəyişərək, verilmiş orbitlər arası keçidlər həyata keçirilmişdir., Научные труды, Выпуск №1-2,2020 (1-105) 2020, Pages 1-10

We introduce Li+ involving cycloadditions between acetylene and ring-like cycloparaphenylenes (CPPs) in theory. Orbital analysis suggests an inverse electron-demand mechanism in which the diene CPP acts as an electron acceptor. Partial electron transfer to Li+ results in a reduced and localized π* orbital of CPP, giving rise to a site-selective reaction with a much smaller barrier.

Cu–S heteroadamantanes are of great interest owing to their relevance to bioproteins. New copper(I) thiolate compounds with additional N-donor functions from phenanthroline ligands have been synthesised. These complexes feature heteroadamantane cage structures with minor deviations in their construction and, therefore, a strong structural relationship. Furthermore, a decanuclear copper–sulfur cluster complex was isolated and shows known structural motifs arranged in a new fashion. Metallothioneins are natural counterparts to these complexes due to their thiolate-rich and polynuclear d10 character. In addition to the structural characterisation, theoretical studies with a triple-zeta basis set have been performed to further understand the building patterns of the reported complexes and their relevance to copper-rich metalloproteins. This includes a Wiberg bond analysis and a full orbital analysis of selected heteroadamantanes to highlight the bonding interactions that connect the copper–sulfur skeletons.

The effect of methanol group on absorption of SO2 by diamine compound was investigated via density functional theory. It was observed that the presence of methanol group increases the binding energy of absorption. According to the result of binding energy, the di-methanol-diamine (D-b) structure can be the best diamine for SO2 absorption and the results of Gibbs energy verified the most thermodynamically favorable structure. According to the weak energy analysis, the absorption interactions in D-b are both vdW and HB interactions. The result of second-order perturbation energy showed that the interaction of the donor atom of diamine with antibonding orbital of S-O (BD*S) in D-b is the highest which points to the most stable structure. According to molecular frontier orbital analysis, it can be concluded that the absorption of SO2 on the diamines is not very strong and desorption of SO2 would be easier than that the strong chemical absorption.

Orbitals and orbital overlap are important concepts in chemistry but are seldom incorporated into medicinal chemistry analyses of drug-target interactions. Our orbital overlap distance D(r) quantifies the size of the "test orbital" that best overlaps with a system's computed orbitals at point r. The overlap distance provides information about all of the occupied orbitals across a molecule, extending frontier orbital (Fukui) analysis and complementing widely used maps of the surface electrostatic potential. We present the first tests of the overlap distance for problems in medicinal chemistry. The overlap distance quantifies the different coordination chemistries of pairs of metal cations possessing similar charges and ionic radii. Combining the overlap distance and electrostatic potential provides a rich picture of the binding sites for chemically "hard" versus "soft" cations in formylglycine-generating enzyme and extends frontier orbital analysis in quantifying the chemistry of promiscuous binders. We conclude by showing how the electrostatic potential and overlap distance combine to give a novel and experimentally testable prediction for improving the in vivo activity of centromere-associated protein E inhibitors. The results motivate including the overlap distance alongside electrostatic potential maps in medicinal chemistry.

Often have you heard that complexes containing close Au(I) contacts are strongly influenced by what has come to be known as aurophilic interactions. In this work, local orbital analysis is carried out to separate competing metallophilic and other weak interactions at the correlated level in three selected molecular crystals. We carefully separate and discuss the different contributions to the total interaction energy of dimers and trimers according to their spatial location, and identify the relative weight in binding. Changes according to the orientation of the monomers have also been computed. Our results show that although metallophilic contacts contribute to the overall stability and the structure of the crystals, they are not at all dominant, and ligand–ligand interactions can easily outweigh the latter.

Decomposing chemical interactions into bonds and other higher order interactions is a common practice to analyse chemical structures, and gave birth to many chemical concepts, despite the fact that the decomposition itself might be subjective in nature. Fragment molecular orbitals (FMOs) offer a more rigorous alternative to such intuition, but might be less interpretable due to extensive delocalisation in FMOs. Inspired by the Principal Component Analysis in statistics, we hereby present a novel framework, Principal Interacting Orbital (PIO) analysis, that can very quickly identify the "dominant interacting orbitals" that are semi-localised and easily interpretable, while still maintaining mathematical rigor. Many chemical concepts that are often taken for granted, but could not be easily inferred from other computational techniques like FMO analysis, can now be visualised as PIOs. We have also illustrated, through various examples covering both organic and inorganic chemistry, how PIO analysis could help us pinpoint subtle features that might play determining roles in bonding and reactions.

A device called Huge Space Shield (HSS) has been put forward for mitigating global warming. This is a space tethers system, which use cables to connect a shielding surface and a mechanism control. In this study, orbital analysis was carried out to choose the best orbit for getting the best effect. Simulation studies were employed to understand the HSS at the beginning of entering the orbit, which were based on completely and semi-simplified model. Therefore, the force analysis gives rise to the system would not fail in the period of running on the orbit. All the results show that the HSS is stable at launch and operation, which can help ease global warming.

In this comprehensive study on unsaturated phosphorus compounds of the type R-P=CR2, R-P=N-R, and R-P=P-R, we investigated how the electronic, spectroscopic, and geometric parameters are influenced by different substituents by means of ab initio and DFT methods. The parent systems are studied with highly accurate theoretical methods and used to benchmark DFT methods. The substituent effects are rationalized based on orbital analysis of DFT calculations for phos-phaalkenes, iminophosphanes, and diphosphenes in comparison with their analogous alkenes and imines. Theoretical data are also compared to experimental data if available. This study provides a broad picture of the use of DFT methods for unsaturated main group systems. Trends obtained from this study will enable a rational molecule design for selective manipulation of electronic and geometric properties.

A detailed orbital analysis of two seemingly ordinary classes of complexes of group 12 dications, [M(NH3)4]2+ and [M(PH3)4]2+, M = Zn, Cd, Hg, holds a surprise. The PH3 complexes are text-book examples of tetrahedral bonding, but in the ammine complexes calculations reveal a remarkable degree of mixing between occupied M (n-1)d and NH3 σπ orbitals. A perturbation-based Fock matrix examination traces the origin of this mixing to an energy resonance and improved overlap of interacting orbitals for NH3 ligands. The possibility of probing this anomalous mixing with valence-to-core X-ray emission spectroscopy (V2C XES) is discussed.

This chapter deals with cheletropic reactions and higher order and multicomponent cycloadditions. The orbital mechanisms of cheletropic reactions are described and selection rules are provided. Singlet carbene cycloadditions including periselectivity and site selectivity, and cheletropic addition and extrusion of sulphur dioxide are presented. The cheletropic extrusions of nitrogen and carbon monoxide are also exemplified. Higher order cycloadditions involving more than 6 electrons are described which include 8-electron [4 + 4] photodimerizations and 10-electron [6 + 4] and [8 + 2] cycloadditions. The stereoselectivity of [6 + 4] cycloadditions has been shown mechanistically. Examples of cycloadditions involving more than 10 electrons including [14 + 2] cycloaddition are provided. Multicomponent cycloadditions with reference to [2 + 2 + 2] and [2 + 2 + 2 + 2] cycloadditions are described. Finally a frontier orbital analysis of cycloaddition involving more than two components is presented.

Context. A low-mass brown dwarf has been recently imaged around HR 2562 (HD 50571), a star hosting a debris disk resolved in the far infrared. Interestingly, the companion location is compatible with an orbit coplanar with the disk and interior to the debris belt. This feature makes the system a valuable laboratory to analyze the formation of substellar companions in a circumstellar disk and potential disk-companion dynamical interactions. Aims. We aim to further characterize the orbital motion of HR 2562 B and its interactions with the host star debris disk. Methods. We performed a monitoring of the system over ~10 months in 2016 and 2017 with the VLT/SPHERE exoplanet imager. Results. We confirm that the companion is comoving with the star and detect for the first time an orbital motion at high significance, with a current orbital motion projected in the plane of the sky of 25 mas (~0.85 au) per year. No orbital curvature is seen in the measurements. An orbital fit of the SPHERE and literature astrometry of the companion without priors on the orbital plane clearly indicates that its orbit is (quasi-)coplanar with the disk. To further constrain the other orbital parameters, we used empirical laws for a companion chaotic zone validated by N-body simulations to test the orbital solutions that are compatible with the estimated disk cavity size. Non-zero eccentricities (>0.15) are allowed for orbital periods shorter than 100 yr, while only moderate eccentricities up to ~0.3 for orbital periods longer than 200 yr are compatible with the disk observations. A comparison of synthetic Herschel images to the real data does not allow us to constrain the upper eccentricity of the companion., Accepted for publication in A&A. 14 pages, 14 figures, 3 tables. Updated to match published paper. Bug in the computation of the distributions of times at periastron passages corrected, minor effects on other orbital parameters

We report the synthesis and X-ray characterization of several oxaphosphirane tungsten(0) complexes especially designed to analyse the intramolecular W–CO(lone pair)⋯π(arene) interaction. The unexpected behaviour of this interaction in the solid state of oxaphosphirane complexes with different degrees of fluorination is rationalized by means of DFT calculations using orbital analysis and Bader's theory of “atoms-in-molecules”.