Electronic excitations in phosphorus-containing molecules. I. Inner shell electron energy loss spectra of PH3, P(CH3)3, PF3 and PCL3

Electron energy loss Spectroscopy has been used to obtain the inner shell electronic excitation spectra of PH₃, PF₃, PCl₃ and P(CH₃)₃ in the phosphorus L-shell (P 2p, 2s) region as well as the respective ligand K -shells (F 1s, C 1s) and L-shell (Cl 2p and 2s) regions. The spectra were obtained under small momentum transfer conditions so that dipole-allowed transitions dominate. An impact energy of 2.5 ke V was used and inelastically scattered electrons were detected at a typical scattering angle of about 1°. A dipoleforbidden transition of unusual character is observed at 135.11 eV in the P 2p spectrum of PCl₃. Although optically forbidden, as indicated by its absence in a soft X-ray absorption spectrum, the intensity of this transition rises very rapidly with increase in momentum transfer.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

Electronic excitation in phosphorus-containing molecules. II. Inner shell electron energy loss spectra of PF5, OPF3 AND OPCl3

Electron energy loss Spectroscopy has been used to obtain the inner shell excitation spectra of PF₅, OPF₃ and OPCl₃ in the P 2p,2s (L-shell) region as well as in the respective ligand K shell (F 1s, O 1s) and L shell (Cl 2p and 2s) regions. The spectra are compared and contrasted with earlier reported spectra obtained on the trivalent phosphorus compounds (PH₃, PCl₃, PF₃ and P(CH₃)₃). The spectra were obtained using an impact energy of 2.5keV and a scattering angle of about 1°. The spectra reported here are typical of molecules with electronegative ligands in that the discrete portions of the spectra show strong transitions to virtual molecular orbitais. In addition, intense features are observed at or just beyond the ionization edge attributable to transitions to trapped inner well states, while broad features further into the continuum can be ascribed to σ^*(P—L) shape-resonances (L = ligand). This resonance assignment was supported by a comparison with the corresponding spectra for PF₃ and PCl₃.     

Inner shell excitation,valence excitation and core ionization in NF3 studied by electron energy-loss and X-ray photoelectron spectroscopies

Electron energy-loss Spectroscopy (EELS) at impact energies of 2.5–3 keV has been used to obtain the electron excitation spectra for the N 1s (K-shell), F 1s (K-shell) and valence shell regions of NF₃. The inner shell spectra were recorded using small angle scattering (?1° ) while the valence shell spectrum was obtained at zero degree scattering angle. The inner shell excitation spectra show a strongly enhanced 1s→ δ^* type transition and continuum features which are typical for molecules with highly electronegative ligands. One of the peaks in an earlier published photoabsorption study of the N 1s region has been shown to be due to a N₂ impurity. The valence shell electron energy-loss spectrum shows a number of transitions which are considered to be mainly due to valence-valence type transitions, with also some evidence of Rydberg structure.The X-ray photoelectron spectra (XPS) of the N 1s and F 1s electrons along with their associated satellite structures have also been recorded using Al Kα (1486.58 eV) radiation. The vertical ionization potentials for the N 1s and F 1s electrons were found to be 414.36 (10) eV and 693.24 (10) eV, respectively. Both spectra exhibit a rich and different satellite structure. These “shake-up” features in the satellite XPS spectra are compared with continuum features of the inner shell electron energy-loss spectra and also with the valence shell spectrum.     

Inner shell excitation of CH 3F,CH 3Cl,CH 3Br and CH 3I by 2.5 keV electron impact

Small angle inelastic scattering of 2.5 keV electrons was used to study inner shell excitation in the methyl halides at energy transfers between 50 and 700 eV. Discrete peaks due to the excitation of carbon K, fluorine K, chlorine L, bromine M_{4, 5} and iodine N _{4, 5} electrons were observed. Correlations through the methyl halide series were used to aid in the assignment of features in the carbon K-shell spectra. A comparison of halogen inner-shell excitation structures with the carbon K-shell excitation structure in the same molecule allowed a complete assignment of all spectral features. The assignments proposed involve promotions of inner shell electrons to unoccupied valence and Rydberg orbitals. On the basis of our assignments of the chlorine L- and carbon K-shell electron energy loss spectra of CH ₃Cl we propose an alternate assignment of the previously reported CH ₃Cl chlorine K-shell photoabsorption spectrum.     

Auger spectra of CO,C2H4, C2N2 and C6H6 adsorbed on Pt(111)

Electron excited carbon KVV Auger spectra of CO, C₂H₄, C₂N₂ and C₆H₆ adsorbed on Pt(111) are compared. By estimating the effective Coulomb interaction between the final-state holes it is possible to associate some features with transitions observed in free molecule spectra, but others must involve at least one electron with energy within the conduction band of the metal. Such “cross-transitions” are associated with strong 2π* character of filled states in the presence of a core hole in molecules such as CO.     

K-Shell energy loss spectra of 2.5 keV electrons in CO2 and N2O

Energy loss spectra of 2.5 keV electrons, scattered by CO₂ and N₂O through small angles, have been studied in the regions around the carbon, nitrogen and oxygen K-edges. With the exception of the oxygen K-shell spectrum of nitrous oxide, the spectra are similar to those observed¹ for the diatomic molecules, N₂ and CO, in that the spectra are dominated by one very intense discrete transition while above the K-edge considerable structure is observed in addition to the normal K-continuum. This structure represents the simultaneous transitions of K-shell and valence shell electrons. The oxygen K-shell spectrum of nitrous oxide is unique in that the higher energy discrete peaks are more intense relative to the first discrete peak compared with the other spectra, while additional continuum structures are very weak. The observed spectra for the carbon K-shell of carbon dioxide and the terminal nitrogen K-shell of nitrous oxide are not in agreement with predictions based on the core analogy model which has previously been shown¹ to apply in the case of N₂ and CO.     

Carbon K-shell excitation spectra of linear and branched alkanes

The electron energy loss spectra of ethane, propane, n-butane, n-pentane, n-hexane, isobutane, isopentane and neopentane in the region of carbon K-shell excitation have been recorded under dipole-dominated conditions (2.8 ke V impact energy, small angle). The spectra are dominated by transitions to unoccupied valence π¹(CH₂, CH₃) and σ¹(C-C) levels. Additional weak features are assigned to Rydberg transitions. The position of the main continuum feature in each spectrum is consistent with the predictions of an empirical relationship with bond length. Systematic variations of spectral intensities are observed which support our assignments. The dominant feature in the K-shell spectrum of ethane, which was previously assigned to C 1s → 3p Rydberg transitions, is reassigned to excitation to a 3p/π¹(CH₃ ), mixed Rydberg/valence orbital (of antibonding σ-¹(C-H) character), in comparison to the other alkane spectra. An improved calibration value of 290.74(5) eV for the energy of the C 1s → π¹ transition in CO₂ is also obtained.     

SiO2 surface defect centers studied by AES

A theoretical model is proposed on how a Si dangling bond associated with an oxygen vacancy on a SiO₂ surface (E_s′ center) should be observed by Auger electron spectroscopy (AES). The Auger electron distribution N_A(E) for the L₂₃VV transition band is calculated for a stoichiometric SiO₂ surface, and for a SiO_x surface containing Si-(e^?O₃) coordinations. The latter is characterized by an additional L₂₃VD transition band, where D is the energy level of the unpaired electron e^?. The theoretical N_A(E) spectra are compared with experimental N(E) spectra for a pristine, and for an electron radiation damaged quartz surface. Agreement with the theoretical model is obtained if D is assumed to lie ≈2 eV below the conduction band edge. This result shows that AES is uniquely useful in revealing the absolute energy level of localized, occupied surface defect states. As the L₂₃VD transition band (main peak at 86 eV) cannot unambiguously be distinguished from a SiSi₄ coordination L₂₃VV spectrum (main peak at 88 eV), supporting evidence is presented as to why we exclude a SiSi₄ coordination for our particular experimental example. Application of the Si-(e^?O₃) model to the interpretation of SiO₂Si interface Auger spectra is also discussed.     

Infrared laser magnetic resonance (LMR) spectroscopy of NO2 (ν2) with a CO2 laser

The infrared laser magnetic resonance spectra for the ν₂ band of NO₂ were observed by using a CO₂ laser. High-K vibration-rotation transitions from ^rR₆(N) to ^rR₁₁(N) (v₂ = 1 ← 0) were observed. The analysis yielded some molecular parameters including two g factors for the excited vibrational state (v₂ = 1).     

Direct-inelastic and trapping-desorption scattering of N2 and CH4 from Pt(111)

Angle and velocity distributions for supersonic chopped beams of N₂ and CH₄ scattered from clean close-packed Pt(111) surfaces are reported. For specular direct-inelastic scattering N₂ and CH₄ velocity distributions can be characterized by empirical relationships used for Ar scattering. For instance, for specular scattering the following relation is found for Ar, N₂ and CH₄: 〈KE_f〉 = A(KE_i) + B(2kT_s), where 〈KE_f〉 is the average final kinetic energy, KE_i is the incident kinetic energy and T_s is the surface temperature. The beam and surface temperature independent coefficients A and B are, respectively: Ar 0.87, 0.17; N₂ 0.79, 0.19 and CH₄ 0.84, 0.25. Unlike Ar, N₂ desorbs from Pt with a Maxwell-Boltzmann velocity distribution near the surface temperature. Qualitatively the trapping probabilities for these molecules on Pt(111) are ordered: Xe > N₂ > CH₄> Ar.     

The temperature dependence of penning ionization electron energy spectra: He(23S)—ar,N2, NO,O2, N2O,CO2

Using two intense thermal energy He(2³S) sources of different temperatures (≈400 and ≈ 1000 K, resp.) and a transmission-calibrated electron energy analyzer with about 30meV resolution, the dependence of He(2³S) Penning ionization electron spectra on collision energy for the target species Ar, N₂, NO, O₂, N₂O and CO₂ have been studied. The energy shifts of the Penning electron energy distributions and the branching ratios for the population of different electronic states in the molecular ions are determined quantitatively and compared for the two different collision temperatures. These results and the shapes of the observed Penning electron energy distributions are discussed in the light of current models for the Penning procen; the observed temperature dependences are correlated with the nature of the ionized orbitals in cases of only one entrance channel (closed shell targets) and, in addition, to the existence of qualitatively different entrance channels (open shell targets).     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

On the assignment of the carbon K-shell spectra of the methyl halides

Electron energy loss spectra of the methyl halides in the region of carbon K-shell excitation have been obtained at higher resolution than those previously reported. The existence of two electronic transitions between 288 and 290 eV in CH₃F is demonstrated. This result conflicts with a recent SCF calculation which suggests that the σ* (C–F) level in CH₃F is unbound and thus predicts the existence of only one electronic transition in this spectral region. Studies of the carbon K-shell spectra of CH₃Br and CD₃Br demonstrate the vibrational origin of some spectral features. These new results support our earlier tentative assignments for the carbon K-shell spectra of the methyl halides.     

Carbon K-shell excitation of C2H2, C2H4, C2H6 and C6H6 by 2.5 keV electron impact

Energy loss spectra of 2.5 keV electrons in the region of the carbon K-edge in C₂H₂, C₂H₄, C₂H₆ and C₆H₆ are report     

The diode laser spectrum of the ν2 band of 14ND3 and 15ND3

The spectra of the ν₂ bands of ¹⁴ND₃ and ¹⁵ND₃ were measured under Doppler-limited resolution with a diode laser spectrometer in order to resolve the K structure of the sR(J, K) and aR(J, K) multiplets. By a simultaneous least-squares analysis of these data, the Fourier spectra of the ν₂ band measured by Jones [J. Mol. Spectrosc.74, 409 (1979)], and the ground-state microwave transitions, sets of improved ν₂-band parameters were obtained, including the sextic centrifugal distortion coefficients.     

Penning ionization electron spectroscopy of H2O,D2O,H2S and SO2

Electron energy peak shifts and peak shapes were determined in the ionization of H₂O, D₂O, H₂S and SO₂ by Ne(³P₂) and He(2¹S, 2³S) metastable atoms. The shifts are large, especially in ionization of H₂O and D₂O into the ionic ground state and are probably mostly due to chemical interaction during the collision.In a previous paper the electron energy distribution curves for ionization of CO, HCl, HBr, N₂O, NO₂, CO₂, COS and CS₂ by helium, neon and argon metastables and the characteristics of this ionization were described¹. In this paper the series of triatomic molecules was extended to the molecules H₂O, D₂O, H₂S and SO₂. Because all these molecules have considerable dipole moments it could be expected that the peak shifts might be enhanced as compared with other triatomic molecules.     

Effect of Bi2O3 content on physical and optical properties of 15Li2O-15K2O-xBi2O3-(65−x) B2O3: 5V2O5 glass system

Multi-component bismuth borate glasses doped with vanadium ions 15Li₂O-15K₂O-xBi₂O₃-(65−x) B₂O₃: 5V₂O_5, (x=3, 5, 7, 10, 12 and 15) have been prepared using conventional melt quench technique. Characterization of the prepared glasses has been done using X-ray diffraction, differential scanning calorimetry and density measurements. The effect of Bi₂O₃ content on the optical properties of the present glass system is studied from the optical absorption spectra recorded in the wavelength range 200-800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi₂O₃ in these glasses is acting partly as network modifier and partly as network former. The variations in the optical band gap energies, density and molar volume with Bi₂O₃ content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity, average crosslink density and the average electronic polarizability are also reported.     

Transport properties of single crystals of CeCu2Si2 and CeNi2Ge2

The resistivity, thermopower and thermal conductivity were measured on single crystals of CeCu₂Si₂ and CeNi₂Ge₂ between 60mK and 300 K. All transport anomalies associated with the unstable 4f-shell in Ce are strongly anisotropic in these noncubic systems.     

The oscillator strengths for C1s and O1s excitation of some saturated and unsaturated organic alcohols,acids and esters

Electron energy loss Spectroscopy (ISEELS) under dipole scattering conditions is used to obtain the carbon and oxygen K-shell oscillator strength spectra of methanol (CH₃OH), propanol (CH₃CH₂CH₂OH), propenol (CH₂=CHCH₂OH), propargyl alcohol (HC≡CCH₂OH), propanoic acid (CH₃CH₂COOH), acrylic acid (CH₂=CHCOOH) and propiolic acid (HC≡CCOOH). A detailed interpretation of these spectra is presented, along with a comparison with the NEXAFS spectra of multilayers of these molecules adsorbed on a Si(111) surface, as recently reported by Outka et al. (Surf. Sci., 185 (1987) 53). Good agreement is found between the multilayer NEXAFS and the gas phase ISEEL spectra, except for the carboxylic acids which differ dramatically in the discrete portion of the O1s spectrum. Possible origins for this difference are discussed. The C1s and O1s spectra of methyl formate (HCOOCH₃) are also reported and interpreted in comparison with the spectra of formic acid and methanol.