X-Ray and X-ray Photoelectron Spectroscopy Studies of the Electronic Structure of Borane Derivatives

This paper reviews the results of electronic structure studies of a number of typical members of borane series by X-ray and X-ray photoelectron spectroscopy using quantum chemical calculations. Fragment analysis of the molecular orbital structure is given. The nature of chemical interaction in boron cluster compounds is studied on models: simple molecules NH₃, BH₃, and BF₃ and their adducts NH₃BH₃ and NH₃BF₃. The electronic structure of B₁₀H₁₂L₂ type compounds with Lewis bases L = NH₃, (CH₃)₂S, (C₆H₅)₃P is analyzed. The complexes are considered in terms of the concept of donor–acceptor interactions between the fragments. The donor–acceptor bond has contributions from both occupied and vacant acceptor orbitals. X-ray photoelectron data on the charged states of atoms in the compounds are overviewed. Electron distribution in complex compounds with transition metals [(1,2-B₉C₂H₁₁)₂M]^–, M = Fe^III, Co^III, Ni^III, and Ni^IV and chain type polycobaltocarborane anions {[(3)-1,2-B₉C₂H₁₁]₂Co _n [(3,6)-1,2-B₈C₂H₁₀]_n-1} ^n– , n = 2-7, is considered.     

Electronic structure of monosubstituted benzenes and X-ray emission spectroscopy

The electronic structure of the benzaldehyde molecule has been studied by X-ray emission spectroscopy. The gas-phase O-K- and C-K-spectra of this compound have been obtained. MNDO quantum-chemical calculations have been carried out. The structure of the MO's of benzaldehyde has been compared with those of benzene and formaldehyde molecules. The character of the p-p interaction of the phenyl and formyl fragments has been considered. The contribution of the latter to the highest occupied molecular orbitals of the-system has been shown to be small.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1033–1037, June, 1994.     

Determination of the energy measurement accuracy for charged particles by their range in nuclear photoemulsion

Ranges of monochromatic muons in nuclear photoemulsion, produced in the ?? ?? ??? _?? decay, are measured by the coordinate method to determine their energy by the range. The variance of the muon energymeasured by this method ?? _?? = (0.11±0.01) MeV, which corresponds to the accuracy of the determination of the charged particle energy by the range in nuclear emulsion ??3.1%. The developed technique will allow electron energy measurements in the 2??-decay (??3 MeV)with an accuracy of (5?C6)%.     

Electronic structure of monosubstituted benzenes and X-ray emission spectroscopy

The electronic structure of fluorobenzene was investigated by X-ray emission spectroscopy (using the F−Kα- and C−Kα-spectra) and quantum-chemical MNDO calculations. Molecular orbitals of fluorobenzene were compared with those of benzene and hydrogen fluoride. The P_π−p_π-interaction between the phenyl ring and the fluorine atom in the fluorobenzene molecule is weak for both the outer and inner π levels. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1454–1460, August, 1997.     

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.     

X-ray emission spectroscopy and electronic. Structure of heterocyclic compounds 2. Thiophene

The electronic structure of has been studied by X-ray spectroscopy. SK , SL _2,3- and CK _±-spectra were obtained. Theoretical spectra were constructed on the basis of ab initio and MNDO calculations and the experimental results were interpreted. The HOMO is an orbital in which the electron density is localized on the carbon atoms. Conclusions about the occupancy of the lowest 3d orbital were reached from the experimental results.For Communcation 1, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1188–1193, September, 1993.     

Fluorine Kα x-ray emission studies of fluorinated organic compounds

Fluorine K_α X-ray emission spectra have been measured and interpreted using UV photoelectron and X-ray photoelectron spectral data and the results of quantum-chemical calculations, for a series of fluorine-containing organic molecules: CH₃F, n-C₅F₁₂, polytetrafluoroethylene, tetrafluoroethylene, 4-XC₆H₄F (X = H, F, NH₂, NO₂), 1,3-difluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,4-difluorobenzene, C₆F₅X (X = H, F, SCH₃, OCH₃, CN, NO₂, C₆F₅, P(OCH₃)₂), pentafluoropyridine, octafluoronaphthalene and 2,4-dinitrofluorobenzene, all in solid or gaseous states. It has been concluded that the fluorine 2pAO contribution to the highest occupied π-orbitals of the benzene ring and π-orbital of the ethylene bond is small: it is somewhat higher for a system of lower-lying π-orbitals and the highest for σ-orbitals. CH₃F is assumed to have hyperconjugation.