Identification of localised and delocalised adsorbate orbitals on W(100) by photoelectron spectroscopy

The comparison of the photoelectron spectra of chemisorbed layers taken with glancing photon incidence and those with normal photon incidence permits a qualitative determination of the degree of delocalisation of the various orbitals at the surface. For glancing photon incidence, both localised and delocalised orbitals can be photoionised. However, for normally incident photons, those orbitals localised around particular atomic sites have a much higher photoionisation cross section than those orbitals extensively delocalised in the plane of the surface. Examples of this behaviour in the spectra of hydrogen and carbon monoxide on W(100) are presented.     

n-σ Mixing in pentatomic heterocyclic compounds of sixth group by photoelectron spectroscopy

The HeI photoelectron energy spectra of the tetrahydro derivates (CH₂)₄X (X = O, S, Se, Te) have been measured and interpreted on the basis of a local C_2V symmetry of the CH₂?X?CH₂ fragment. Mixing of the so called “non-bonding” electrons of the heteroatom with the σ_π system is apparent from the shape of the first photoelectron band and from a comparison of the absolute values of the first ionization energies with those of the corresponding H₂X molecules. Such mixing is the highest for the oxygen derivative and gradually decreases on going toward the tellurium compound.     

Molecular orbitals and photoelectron spectra of some titanium(IV) organometallic compounds

The photoelectron spectra of some titanium(IV) organometallic compounds are reported, and the data and the bonding in the compounds are discussed with the aid of extended CNDO/2 calculations.     

Bond types of molecular orbitals and the photoelectron spectrum

The vibrational structures of the photoelectron spectra for diatomic molecules can be accounted for in terms of the slope of the orbital energy curve in the conventional correlation diagram with respect to internuclear distance. The vibrational structures of the photoelectron spectra for simple polyatomic molecules HCN, C₂H₂, and AH₂ type of hydrides can also be accounted for in terms of the slopes of the orbital energy curves in the correlation diagrams with respect to angles, as well as distances. Among all correlation diagrams, the slopes in the distance correlation diagram are related to the criterion for bond type—the positive for “bonding,” the negative for “antibonding,” while slopes with small magnitudes for “nonbonding.” The Fock matrix elements within the bond orbital basis provide heuristic and systematic rationalization of the slopes for the orbital energy curves. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 53–65, 2001     

Electronic couplings in organic mixed-valence compounds: the contribution of photoelectron spectroscopy

We show that the electronic coupling in strongly coupled organic mixed-valence systems can be effectively probed by means of gas-phase ultraviolet photoelectron spectroscopy (UPS). Taking six diamines as examples, the UPS estimates for the electronic couplings H(ab) are compared with the corresponding values determined from the intervalence charge-transfer absorption bands and from electronic structure calculations. Similar trends are observed for the H(ab) values estimated from UPS and optical spectra; this provides support for the applicability of Hush theory to strongly coupled organic mixed-valence systems. The UPS electronic couplings are found to be somewhat smaller than those from optical spectroscopy, which is attributed to the role of vibronic coupling to symmetrical modes; when corrected for this vibronic coupling, the UPS H(ab) estimates confirm that triarylamine-based mixed-valence systems are close to the class-II/class-III borderline.     

Structure of X-ray photoelectron, emission, and conversion spectra and molecular orbitals of uranium compounds

The fine structure of X-ray photoelectron spectra of uranium compounds in the range of electron binding energies from 0 to ∼50 eV is largely determined by the electrons of the outer and inner valence molecular orbitals arising from the valence atomic shells, including the U6p and Lns low-energy occupied atomic shells. This result is in agreement with the data of the electronic structure calculations of these compounds and confirmed by the nuclear electron (conversion) and X-ray emission spectroscopic investigations. It is shown that the fine structure of X-ray photoelectron spectra associated with the electrons of inner valence molecular orbitals makes it possible to judge the participation of the electrons of the occupied atomic shells in chemical bonding, the structure of the nearest environments of the atom, and the bond lengths in the compounds. The overall contribution of the electrons of these molecular orbitals to the absolute value of binding energy may prove to be comparable to the contribution of the electrons of the outer valence molecular orbitals to atomic bonding. This is a new and important fact in chemistry. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1037–1046, November–December, 1998.     

Thermodynamic analysis of strain in the five-membered oxygen and nitrogen heterocyclic compounds

Cyclopentane is conventionally strained. Replacement of a carbon atom by a heteroatom obviously impacts angular strain in the five-membered ring compounds. Changes of strains in the five-membered cycles are also caused by a double bond or atttached benzene rings. We studied the thermochemical properties of Indane, 2,3-dihydrobenzofuran, indoline, N-methyl-indoline, carbazole, and N-ethyl-carbazole to obtain a better quantitative understanding of the energetics associated with these compounds containing five-membered ring units. We used combustion calorimetry, transpiration method, and high-level first-principles calculations to derive gaseous enthalpies of formation of the five-membered heterocyclic compounds. Our new values together with the selected values for parent heterocyclic compounds, available from the literature, were used for calculation of the strain energies H(S) of five-membered C-, N-, and O-containing cycles. Quantitative analysis of the resulting stabilization or destabilization of a molecule due to interaction of benzene rings with the heteroatom has been performed.     

Oximes of five-membered heterocyclic compounds with two heteroatoms 2. Reactions and biological activity (Review)

Data on the reactions of oxazole, thiazole, pyrazole, and imidazole aldoximes, ketoximes, amidoximes, and their derivatives are reviewed. The synthesis of new heterocycles based on the oximes of five-membered heterocyclic compounds with two heteroatoms are considered separately. The principal results from investigation of the biological activity of the ethers of these oximes are also presented. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1123–1155, August, 2007.     

Oximes of five-membered heterocyclic compounds with two heteroatoms. 1. Synthesis and structure (Review)

Data on the production and structure of oxazole, thiazole, and imidazole aldoximes, ketoximes, and amidoximes and their derivatives are reviewed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–504, April, 2007.     

Monitoring of liquid-phase organic reactions by photoelectron spectroscopy

There are strings attached: after linking the reacting groups to head groups of ionic liquids to drastically lower the vapour pressures of the reactants, ordinary liquid-phase organic reactions can be monitored by in situ X-ray photoelectron spectroscopy. This approach is demonstrated for the nucleophilic substitution of an alkyl amine and an alkyl chloride moiety, which are attached to the cation and anion of ionic liquids, respectively.     

Oximes of five-membered heterocyclic compounds with three and four heteroatoms 1. Synthesis and structure (review)

Data on the production methods and structure of triazole, tetrazole, dioxazole, oxadiazole, and thiadiazole aldoximes and ketoximes and their derivatives are reviewed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 803–816, June, 2008.     

Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped metal-phthalocyanine compounds

We have performed a comparative study of the electronic properties of six different electron-doped metal-phthalocyanine (MPc) compounds (ZnPc, CuPc, NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by means of potassium intercalation. Despite the complexity of these systems, we find that the nature of the underlying molecular orbitals produces observable effects in the doping dependence of the electrical conductivity of the materials. For all the MPc's in which the added electrons are expected to occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping dependence of the conductivity has an essentially identical shape. This shape is different from that observed in MPc materials in which electrons are also added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The observed relation between the macroscopic electronic properties of the MPc compounds and the properties of the molecular orbitals of the constituent molecules clearly indicates the richness of the alkali-doped metal-phthalocyanines as a model class of compounds for the investigation of the electronic properties of molecular systems.     

Comparative crystal-chemical analysis of d-metal sulfides, selenides, and tellurides and binary compounds

The structures of d-metal sulfides, selenides, and tellurides containing a tetrahedral complex anion have been compared to 1573 representatives of the topological types of binary compounds with the use of the TOPOS structural topological program package. The cases of similarity between these classes of compounds are found and discussed. Based on the results of topological analysis of ionic matrices, the rules are formulated that allow one to predict specific features of the structures of salts with complex chalcogen-containing anions.     

Electronic structure of some penta-atomic heterocyclic molecules studied by gas-phase HeI and HeII photoelectron spectroscopy

Implications on the electronic structure of changing substituents in a series of four penta-atomic heterocyclic compounds, 2,4-thiazolidinedione, rhodanine, pseudothiohydantoin, thiohydantoin, are investigated by gas-phase u.v. photoelectron spectroscopy. Both HeI and HeII spectra are reported and discussed also on the basis of CNDO/2 calculations. The most important interactions occurring in these molecules are the through-space ones between the π orbitals of functional groups in β position. The HOMO in all the molecules has significant contribution from S 3p orbitals.     

Formation of uncondensed binuclear heterocyclic compounds in the thio-claisen rearrangement of heteroaromatic sulfides

Allyl hetaryl Sulfides with an allyl fragment that is part of a heteroaromatic ring undergo a [3,3]-sigmatropic rearrangement when they are heated in various solvents, as a result of which uncondensed binuclear heterocyclic compounds are formed. On the basis of kinetic data it was shown that the inclusion of the vinyl or allyl fragment of a sulfide in the composition of the heteroaromatic ring hinders the rearrangement more, the higher the aromatic character of the heteroring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1348–1351, October, 1983.     

X-ray emission spectroscopy and the electronic structure of heterocyclic compounds

The electronic structure of the pyridine molecule has been investigated by x-ray emission spectroscopy. The NK _y and CK _y emission spectra have been measured. Ab initio and MNDO calculations have been carried out and individual bands in the spectra have been identified subsequently. The calculations produce spectral contours which approximate those of the experimental spectra.For Communication 3 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1484–1487, November, 1993.