Silicon-nitrogen bonding in silatranes: assignment of photoelectron spectra

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

Ab initio calculations and assignment of photoelectron spectra of maleic and succinic anhydride

The results from ab initio calculations on maleic and succinic anhydride are presented. A good correlation is obtained between the calculated orbital energies and the ionization potentials obtained from the photoelectron spectra of the molecules. The photochemistry of cyclohexadiene is discussed on the basis of the concepts of through bond and through space interaction.     

The conformation,UV-absorption spectra and photoelectron spectra of phenoxachalcogenins

The analysis of dipole moment data obtained for dibenzo-p-dioxin, phenoxathiin, phenoxaselenin and phenoxatellurin in benzene at 25°C in conjunction with EHT calculations of the ocnformational energies show that these molecules adopt a non-planar conformation in solution. Each of the phenoxachalcogenins is folded along the axis connecting the two heteroatoms. A butterfly flapping motion about the planar conformation canot be excluded. The uv and photoelectron spectroscopic data support the conclusions drawn from the dipole moment studies. The spectroscopic data were interpreted with the help of SCF-PPP-CI calculations.     

The photoelectron spectra of the OH and OD radicals

He(I) photoelectron spectra of the hydroxyl radical show ionizations corresponding to the production of OH⁺ (OD⁺) in the states X ³Σ^? and ¹Δ at ionization potentials of 13.01 eV and 15.20 eV respectively. The excitation energy of the ¹Δ state is in very good agreement with that predicted by calculation and experiment; vibrational spacings in the X ³Σ^? state agree with emission spectroscopic data.     

The He-I photoelectron spectra of uranocene and thorocene

The bonding in unranocene and thorocene is discussed in the light of their photoelectron spectra and ionization of 5f electrons is identified.     

Simulating the photoelectron spectra of rare-gas clusters

Motivated by the recent experiments of the Swedish group [M. Tchaplyguine, R. R. Marinho, M. Gisselbrecht et al., J. Chem. Phys. 120, 345 (2004)], we simulate the photoelectron spectra of pure xenon and argon clusters. The clusters are modeled using molecular dynamics with Hartree-Fock-dispersion type pair potentials while the spectrum is calculated as the sum of final state energy shifts of the atoms ionized within the cluster relative to the isolated gas phase ion. A self-consistent polarization formalism is used. Since signal electrons must travel through the cluster to reach the detector, we have accounted for the attenuation of the signal intensity by integrating an exponentially decaying scattering expression over the geometry of the cluster. Several different approaches to determining the required electron mean free paths (as a function of electron kinetic energy) are considered. Our simulated spectra are compared to the experimental results.     

UV spectra of vinyl chalcogenides: Correlation with the photoelectron spectra

The electron absorption spectra of alkylvinyl chalcogenides (CH₂=CHEAlk, E = S, Se, Te) were analyzed with consideration of the photoelectron spectroscopic data. The following sequence of electronic transitions was found in their UV spectra:

Calculation of photoelectron spectra of chloromethanes

Photoelectron spectra of chloromethanes have been calculated by the SCF Xα SW method. Results of the present work are in significantly better quantitative agreement with experiment data than are the results of other theoretical methods.     

Electronic structure and photoelectron spectrum Assignment of allene

In this paper a series of ab initio SCF and configuration calculations were reported forthe ground state and excited states X~2E, A~2E,~2B_2 and ~2A_1 of allene.For ground state X~2E Jahn-Teller distorsion was discussed and a twisted angle of 50° and a torsional barriers of 0.21—0.51 eVwere derived.Based on calculated results,the experimental photoelectron spectrum of allene has beenassigned.     

AM1 studies of photoelectron spectra

Five ionization potentials for thesp,ac andsp, sp conformers of (acetylthiomethyl)trifluorosilane MeC(O)SCH₂SiE₃ and six ionization potentials for the same conformers of (benzoylthiomethyl)trifluorosilane PhC(O)CH₂SiF₃ were calculated by the semiempirical AM1 method. The resulting values are in good agreement with the data of photoelectron spectroscopy only for thesp.ac conformers. The structure of the preferred conformer of (acetylthiomethyl)trifluorosilane was confirmed by measurement of its dipole moment in the gas phase. The influence of the long-range inductive effect (field effect) on the energy of nonbonding electrons of the carbonyl oxygen atom in the series of acetic acid derivatives was observed. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 236–241, February, 1998.     

AM1 study of photoelectron spectra

A correlation was found between the group dipole moments of substituents determined from the dipole moments of ethylene derivatives and the second ionization potentials of allene derivatives corresponding to the -MO of the C()-C() bond. It was shown that the concept of the effect of the substituent field cannot completely explain the observed phenomena, and the energies of the second ionic states of bromoallene and alkoxyallenes are lowered because of the interaction between nonbonded fragments through the systems of the compounds. It has been found that, in terms of orbital approximation, this interaction causes electronic destabilization of theanti-planar (trans) conformers of methoxyallene and methyl vinyl ether compared to theirsin-planar (cis) forms.For Part 5, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–54, January, 1995.     

AM1 studies of photoelectron spectra

Deep-lying π- and σ-orbitals of 10-alkylphenothiazines were studied by photoelectron spectroscopy and quantum-chemical AM1 calculations. It was demonstrated that in 10-ethylphenothiazine the lone electron pair of the S atom interacts with the π-system of the aromatic fragments. The π-MOs, whose energies are a function of the dihedral angle between the planes of the benzene rings of phenothiazines and are independent of the degree of pyramidality of the N atom, were found. The differences in the energy of these MOs were used for estimating equilibrium dihedral angles of tricyclic molecules in the gaseous phase. These values differ only slightly from those observed in the solid phase. The replacement of the hydrogen atom at position 10 by the methyl group leads to a decrease in the dihedral angle, leaving the orientation of the substituent unchanged. The orbital energies of phenothiazines, which were calculated by the AM1 method, adequately reflect the order of changes in the ionization potential. However, contributions of the two highest occupied π-MOs to the total charges on the N and S atoms are inconsistent with the experimental data. For Part 10, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–1548, August, 1998.     

The nature of the electronic states and photoelectron spectra of oxyanion crystals

The densities of states, atomic charges, and partial components were calculated by the B3LYP method for lithium, sodium, and potassium nitrites, nitrates, chlorates, perchlorates, sulfites, and sulfates using a localized basis of atomic orbitals and CRYSTAL06 software. The calculated densities of states N(E) are in good agreement with the experimental photoelectron spectrum (UPS). The crystallographically nonequivalent metal and oxygen atoms are in different charged states, which leads to a splitting of the N(E) bands.     

The photoelectron spectra of 4-methylene thiacyclohexane derivatives through-bond interaction

The photoelectron spectra of 4-methylene thiacyclohexane, 4-difluo romethylene thiacyclohexane and trans-2-methylene-6-thiaperhydronaphthalene are described and compared with thiacyclohexabne, difluoromethylene-cyclo hexane and cis-2-methylene-6-thiaperhydronaphthalene.A through bond interaction between the sulphur lone pair and the vinyl-π-system is observed. The results are discussed in relation with the sigma-coupled transition observed in the electronic absorption spectra of the dicyano methylene derivatives by P. Pasman.     

Valence band photoelectron spectra of transition-metal cyanides

X-ray photoelectron spectra of the valence bands of NaCN, Li₄Fe(CN)₆, Li₃Fe(CN)₆, Ni(CN)₂, Li₂Pt(CN)₄ and LiSCN have been measured and interpreted. Normalization of the valence-band intensities by equalization of the nitrogen is intensities made it possible to distinguish between cyanide and transition-metal bands. The spectrum of CN⁻ is similar to that of the iso-electronic molecules N₂ and CO. The transition-metal bands occur at a lower binding energy than the CN⁻ bands and do not show structure. From the intensities we conclude that much less mixing of the metal and ligand orbitals takes place than indicated by recent MO calculations.