ESCA applied to polymers. XXVI. Investigation of a series of aliphatic,aromatic, and fluorine-containing polycarbonates

The absolute and relative binding energies for the C_1s, O_1s, and F_1s core levels have been determined using x-ray photoelectron spectroscopy (ESCA) for a series of aliphatic, aromatic, and fluorine-containing polycarbonates. Comparisons of these experimentally determined, core-level binding energies with theoretical calculations using the ground-state potential model in the CNDO/2 SCF MO formalism as well as model compounds have been made on the C_1s and O_1s core levels. The degree of polymerization for low-molecular-weight fluorine-containing polycarbonates, as determined from ESCA measurements, is compared to measurements by vapor-phase osmometry and ¹⁹F-NMR.     

Applications of ESCA to polymer chemistry. X. Core and valence energy levels of a series of polyacrylates

The core and valence levels of a series of poly(alkyl acrylates) have been studied by ESCA. From an analysis of the individual component peaks for the C_1s and O_1s core levels and from comparison of relative area ratios it is shown that ESCA may be applied to the study of surface compositions. The evidence presented strongly suggests that on the ESCA depth-profiling scale the technique statistically sample the repeat units with no evidence for preferential orientation of side chains at the surface. For some samples, ESCA provides evidence for a degree of surface oxidation and hydrocarbon contamination. The valence energy levels are shown to be characteristic of the polymer system. The measured absolute and relative binding energies of the core levels have been compared with model calculations using the charge-potential model in the CNDO/2 SCF MO formalism.     

Applications of ESCA to polymer chemistry. XI. Core and valence energy levels of a series of polymethacrylates

The core and valence energy levels of a series of poly(alkyl methacrylates) have been studied by ESCA. Surface compositions have been determined both from a comparison of area ratios for the O_1s and C_1s core levels and from the relative areas for the individual component peaks for these levels. The evidence presented suggests that on the ESCA depth-profiling scale the technique statistically samples the repeat unit with little or no evidence for preferential orientation of the alkyl side chain at the surface. Little evidence was found for either surface oxidation or hydrocarbon contamination at the surface of the samples studied. The valence energy levels are shown to be characteristic of the polymer system.     

Comparisons of glow discharge polymerization between hexamethyldisilazane and trimethylsilyldimethylamine

Glow discharge polymerization between hexamethyldisilazane (HMDSZ) and trimethylsilyldimethylamine (TMSDMA) was compared by means of infrared spectroscopy and ESCA analysis. Infrared spectra pointed out differences in chemical structure between the polymers prepared from the two monomers, although the two polymers were mainly composed of resembling units such as Si? CH₃, Si? CH₂, Si? H, Si? O? Si, and Si? O? C groups: (i) The polymers prepared from TMSDMA contained N → O group, but the polymers from HMDSZ did not contain this group. (ii) Influences of the W/FM parameter (W is the input energy of rf power, F the flow rate of the monomer, and M the molecular weight of the monomer) appeared on decreasing the C? N group and increasing the C?O group in the TMSDMA system, but little influence appeared in the HMDSZ system. ESCA spectra (C_1s, Si_2p, and N_1s core levels) supported the differences between the two polymers elucidated by infrared spectroscopy, and pointed out differences in susceptibility of the Si? N bond to plasma: The N? Si sequence of TMSDMA was completely ruptured in discharge to yield polymers, and the Si? NH? Si sequence of HMDSZ remained in considerable amount.     

Non empirical LCAO SCF MO investigations of electronic reorganizations accompanying core ionizations

Calculations have been carried out on an extensive series of molecules for both the neutral species and core ionized states. Substituent effects on C_1s , N_1s , O_1s , and F_1s levels have been investigated and where available comparison has been drawn with experiment. Comparison with Koopmans' theorem has allowed a relatively detailed study of change in relaxation energies as a function of substituent effect on a given core level. Whilst for C_1s levels the computed shifts in core binding energies are approximately linearly related to differences in relaxation energies for the N_1s , O_1s , and F_1s levels, the relative electronegativity of the substituent can invert this correlation. The empirical correction of Koopmans' theorem for differences in relaxation energies at different sites has been investigated for large molecules. The results compare well with direct hole state calculations.     

A theoretical investigation of molecular core binding and relaxation energies in a series of oxygen-containing organic molecules of interest in the study of surface oxidation of polymers

Nonempirical LCAO MO SCF computations (in the ΔSCF formalism) have been carried out of binding energies and relaxation energies for an extensive series of oxygen-containing organic systems encompassing most of the common functionalities. The molecules for which experimental data are available for comparison demonstrate the adequacy of the treatment for describing the relative binding energies for both the C_ls and O_ls core levels. A sound basis is therefore provided for the discussion of relative core binding energies (C_ls and O_ls) for functionalities for which experimental data are not available, that is, hydroperoxides, peroxides, peroxyacids, and peroxyesters, a knowledge of which is essential for investigations of the surface oxidation of polymers by means of ESCA. C_ls shifts are discussed in terms of primary and secondary substituent effects of oxygen, which greatly simplify the analysis of complex unresolved spectra, whereas for the O_ls levels a similar but less straightforward situation exists. The relaxation energies associated with both C_ls and O_ls core ionization follow a dependence on the binding energy for a given structural type.     

Structures and energies of seleno derivatives of biuret.Ab Initio comparative studies of diselenobiuret, selenobiuret, and selenothiobiuret

Ab initio studies (LCAO-MO method) on conformers of three seleno derivatives of the biuret molecules diselenobiuret [I], selenobiuret [II], and selenothiobiuret [III] were carried out at the Hartree-Fock (HF) and MP2 levels. The molecular geometries of these species were fully optimized at the HF level and characterized by analysis of the harmonic vibrational frequencies using a split-valence triple-zeta basis set augmented by a set ofd polarization functions on heavy atoms andp polarization functions on hydrogen atoms [TZP(d, p)]. The total energies of the HF-optimized structures were calculated at the MP2 (frozen core) level using a larger TZP (2df, 2pd) basis set. The potential energy searches revealed a total of 11 minimum-energy conformers (assigned astrans-trans, trans-cis, cis-trans, andcis-cis) and seven transition-state species for the title molecules. The two predicted conformers for diselenobiuret (Ia=trans-trans andIc=cis-cis) are characterized byC ₂ and the third byC _s symmetry. For selenothiobiuret two forms (IIIa=trans-trans andIIId=cis-cis) possessC ₁ and two (IIIb=trans-cis andIIIc=cis-trans) possessC _s symmetries, respectively. For selenobiuret, four formsIIa=trans-trans (C₁),IIb=trans-cis (C _s),IIc=cis-trans (C ₁), andIId=cis-cis (C₁), were obtained as a result of gradient optimization. Comparison of the relative energies for the considered species indicated that thecis-trans forms are the most stable conformations for all three systems at both the HF and MP2 levels of theory.     

Plasma polymerization. II. An ESCA investigation of polymers synthesized by excitation of inductively coupled RF plasma in perfluorobenzene and perfluorocyclohexane

The plasma polymers formed in glow and nonglow regions of an inductively coupled RF plasma with perfluorobenzene and perfluorocyclohexane are discussed as a function of operating conditions of the plasma by means of ESCA. The core levels of the plasma polymers are shown to be strikingly different but characteristic of a well-defined but complex polymerization scheme. For the nonglow regions fluorine incorporation is shown to be greater than for polymers prepared in the glow regions and a preponderance of CF₂ features is apparent. Perfluorobenzene deposits polymer faster than perfluorocyclohexane and changes in component composition of the C_1s profile are studied as a function of operating conditions of the gas plasma.     

Sur un traitement unifie des deplacements chimiques en spectrometrie photoelectronique de rayons—X (ESCA), des moments dipolaires et des polarisabilites

The simplest and most general model for interpreting ESCA chemical shifts, the physical meaning of which is very clear, also allows the discussion of dipole moments and polarisabilities. Sixty-eight ESCA chemical shifts of C_1s, N_1s, O_1s and F_1s in 41 differently-substituted compounds (?F, ?Cl, ?Br, ?OH, ?NH₂), saturated or unsaturated (aldehydes, ketones, acids), have been calculated with this model from electric charge distribution; the mean quadratic deviations are respectively ±1.1 eV for C, ±1.6 eV for N, ±0.8 eV for 0, ±0.7 eV for F.With this model, electric charge repartitions can be deduced from ESCA data, even for aromatic molecules. The calculated electric dipole moments for 12 fluorinated aromatic molecules agree very well with experimental results. Other data have been calculated for molecules for which experimental data are not yet available, including examples where heavy atoms are present.     

Application of an ion-fitted pseudopotential to HF,H2O,NH3, BeO,and HCl in a Gaussian lobe basis

The core potentials for atoms of atomic numer 1–18 fitted to ion spectra by Chang, Habitz, Pittel, and Schwarz have been extended to the molecular case in a Gaussian lobe basis by using a six-Gaussian (6G-POT ) representation for the exponential factors of the atomic core potentials. In a (9s/5p/1d) basis the 6G-POT one-electron energies, dipole moments, and Mulliken charges are improved over a one-Gaussian potential form for HF, NH₃, and H₂O; BeO also yields good agreement within 2.6% of the experimental bond length. For HCl, the core potential shows larger errors in the dipole moment (7%) and one-electron eigenvalues (2%), but a 75% saving in computer time is realized for HCl compared with only about 35% for first-row systems using the 6G-POT core potentials. Analytical expressions are given to extend the 6G-POT method up to s, p, d, f, and g valence shells.     

Ab initio calculations on NO2 and NO 2 − : Optimization of diffuse Gaussian exponents

Ab initio calculations of NO₂ and NO ₂ ⁻ , using a Dunning [4s3p] basis augmented by 1 component diffuses andp functions were carried out. The SCF energies of NO₂ and NO_2/− (ground states) as a function of O _s , O _p , N _s , and N _p diffuse function exponents are given and discussed. The curves show some unexpected features which make the optimization of the diffuse function exponents problematic. The SCF vertical electron detachment energy for NO ₂ ⁻ as a function of the diffuse O _s , O _p , N _s , and N _p exponents is then discussed. Except for the case of O _p , the detachment energy is essentially independent of the O _s , N _s , and N _p exponents. Finally, results of SCF and MCSCF/CI calculations of the electron affinity of NO₂ are given and compared with experiment. Work performed under the auspices of the Division of Basic Energy Sciences of the U.S. Department of Energy. By acceptance of this article, the publisher and/or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.     

Long-range interaction between 1s and 2s or 2p hydrogen atoms

Long-range interaction energy between two hydrogen atoms has been computed in the second order of the perturbation theory. All states of the system arising when one of the atoms is in the 1s and the other in the 2s or 2p state have been considered. The energy represented by a series expansion in inverse powers of the internuclear distance, R, has been computed up to the terms in R^?8. The results are believed to give reliable interaction energies for R > 15 a.u. Accurate interaction energy for two ground-state hydrogen atoms has also been obtained up to the terms in R^?10. Results for the B′ ¹∑ state are employed to discuss the experimental ground-state dissociation energy of H₂, D₂, and HD. For H₂ all values of the dissociation energy obtained from various experimental absorption limits, by using the computed potential energy curve to separate off the effect of rotation, are shown to be satisfactorily consistent. The resulting total energy of H₂ is, however, higher than the most accurate theoretical value.     

Surface aspects of the heat treatment of polyethylene terephthalate as revealed by ESCA

The changes in surface structure and bonding of PET films has been monitored as a function of temperature by means of ESCA. By monitoring both the C_1s and O_1s core levels it is shown that at remarkably low temperatures there is a reduction in oxygen functionality. This contrasts with the results in the literature relating to bulk techniques for monitoring thermal degradation.     

Theoretical studies of organometallic compounds. III. Structures and bond energies of FeCHn and FeCH (n = 1, 2, 3)

The geometries and dissociation energies for the Fe? C and C? H bonds of FeCH_n and FeCH (n = 1, 2, 3) have been calculated by ab initio quantum mechanical methods using different effective core potential models and Møller–Plesset perturbation theory. The HW3 ECP model, which has a configuration [core] (n?1)s², (n?1)p⁶, (n?1)d¹, (n)s^m for the transition metals, is clearly superior to the larger core LANL1DZ ECP model with the configuration [core] (n?1)d¹, (n)s^m. The Fe? C bond energies calculated at correlated levels using the HW3 ECP are in much better agreement with experiment than the LANL1DZ results. This effect is mainly due to the higher number of correlated electrons rather than the inclusion of the outermost core electrons in the Hartree–Fock calculation. At the PMP4/HW3TZ/6-31G(d)//MP2/HW3TZ/6-31G(d) level, the theoretically predicted Fe? C bond energies for FeCH are in the range of 80% of the experimental values and have nearly the same accuracy as all-electron calculations using large valence basis sets and the MCPF method for the correlation energy. © 1992 by John Wiley & Sons, Inc.     

Triazènes. Etude XPS. et 1H-RMN. des complexes mercuriques des diaryl-1,3-triazènes

XPS. and ¹H-NMR. spectra of 1,3-diaryltriazenes complexes of Hg(II) The core binding energies C 1s, N 1s, Hg 4f_7/2, Hg 4f_5/2 in 7 symmetrical p-substituted 1,3-diphenyltriazenes complexes of Hg(II) have been measured by XPS. Within the limits of experimental error (± 0.2 eV) only one N 1s signal could be detected. This indicates the equivalence of the 3 N-atoms. Invariance of C 1s, N 1s, Hg 4f_7/2, Hg 4d_5/2 signals with the para substituents on the phenyl ring is explained on the basis of ionic character in the Hg, N bond. These results are corroborated by the ¹H-NMR. spectra.     

Applications of ESCA to polymer chemistry. XII. Structure and bonding in commercially produced fluorographites

A series of fluorinated graphites, Fluorographites, of varying fluorine content has been examined by ESCA, and the chemical shifts and relative intensities of the core electron lines yield a consistent picture of the compositions and structures in the surface regions of the materials. Fluorographites of composition (C₁F_0.81)_n to (C₁F_1.00)_n are fully fluorinated in the outermost ～40 Å and consist of a bulk structure composed of tertiary →CF groups with ? CF₂? groups at the prismatic edges of the fluorinated graphite layers. This is also the case for (C₁F_1.05)_n, but, in addition, some of the C? C bonds involving edge →CF carbons are broken and replaced by C? F bonds, giving a higher concentration of ? CF₂? groups at the outermost surfaces of the particles of this material. The ESCA data for (C₁F_0.25)_n are consistent with a structure comprising six-membered aromatic rings in which each ring carbon is attached to a →CF group acting as a bridge among three similar rings, with the C? F bonds alternately pointing up and down with respect to the plane defined by the carbon atoms. At the immediate surface the valence requirements of the carbon atoms at the prismatic edges of the graphite-like layers are satisfied by bonding with oxygen. This is also the apparent structure of (C₁F_0.37)_n, but in addition there exist discrete regions of composition (C₁F₁)_n distributed uniformly throughout this material. The Fluorographites (C₁F_0.34)_n, and (C₁F_0.40)_n, and (C₁F_0.63)_n consist of blocks of C₁F₁ stoichiometry and blocks of unreacted graphite. The presence of ? CF₂? groups and the complete absence of oxygen in the surface regions of these Fluorographites suggests that the prismatic edge sites are fully fluorinated. The inhomogeneous block-like structures of (C₁F_0.37)_n, (C₁F_0.37)_n, and (C₁F_0.34)_n, (C_1F0.40)_n, and (C₁F_0.63)_n, give rise to differential sample charging, resulting in apparent shifts in the binding energy scales between the spectral components originating from different regions of the samples. Such differential sample charging is also described for a number of mixtures of the Fluorographites and of graphite with the Fluorographites. It is pointed out that in view of these results it is necessary to exercise considerable caution in using the ESCA lines of an added compound as a reference in measuring core electron-binding energies.     

Effect of the exchange integral K2s2p on the 2p-orbitals of the 1P and 3P states of the beryllium isoelectronic sequence arising from the configuration (1s)2(2s)(2p)

The ¹P and ³P states arising from the configuration (1s)²(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E⁰ + K_2s2p and E⁰ - K_2s2p, respectively. K_2s2p is the exchange integral between the 2s and 2p electrons and E⁰ is the energy of a model in which K_2s2p is deleted. First we calculate the 2s- and 2p-orbitals in this model. Second, by taking account of K_2s2p in this model, effects of this term on the 2p-orbitals in the ^1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater-type orbital set; (1) for Be and B⁺, the 2p-orbital of the ¹P state is broader than that of the ³P state; (2) for C²⁺, the extension of the 2p-orbital in the two states is almost the same; (3) for O⁴⁺ and Ne⁶⁺, in contrast to Be and B⁺, the 2p-orbital of the ¹P state is tighter than that of the ³P state.     

Application of the Equivalent Bond Orbital Model to the C2s-Ionization Energies of Saturated Hydrocarbons

It is shown that the ab initio STO-3G treatment applied to simple saturated linear, branched and cyclic hydrocarbons, assuming standard geometries, yields orbital energies ? for their canonical orbital φ_j which correlate perfectly with the observed C_2s ionization energies I, if Koopmans' approximation is accepted. Applying the Foster-Boys localization procedure to these canonical orbitals φ_j leads to localized orbitals λμ and their corresponding Hartree-Fock matrix F_λ = (F_λ,μv). An examination of the matrix elements F_λ,μv, i.e. of the self-energies A_μ = F_λ,μμ of the localized CC- and CH-orbitals λ_μ and of the cross terms F_{λ, μv} (μ ≠ v) between them, leads to the conclusion that a satisfactory approximation should be obtained by setting A_μ = A for all μ, F_λ,μv = B if λ_μ and λ_v are vicinal and neglecting all other cross terms. The resulting model is nothing but the well-known equivalent bond orbital model of Lennard-Jones & Hall, which however can now be calibrated using the known C_2s-ionization energies of hydrocarbons. Due to the discrete structure and the wider range (∽ 8 eV) of the C_2s band systems in the photoelectron spectra of these molecules this leads to a more satisfactory parametrization than using the narrower and badly resolved C_2p band system. Comparison of calculated band positions using the calibrated model with observed C_2s-band ionization energies for a series of hydrocarbons reveals that the simple equivalent bond orbital model is better than one might have expected.