Showing papers on "Photoemission spectroscopy published in 1970"
TL;DR: In this article, the inner shell ionization energies calculated from Koopmans' theorem were shown to relate to a weighted average energy for singly and multiply excited states in the photoelectron spectrum, analogous to the Franck-Condon principle in molecular spectroscopy.
334 citations
TL;DR: In this article, the authors used X-ray photoelectron spectroscopy (XPS) to measure splittings of metal-atom electron binding energies in both inorganic solids and gases.
Abstract: X-ray photoelectron spectroscopy (XPS) is used to measure splittings of metal-atom electron binding energies in both inorganic solids and gases. These splittings are due to the various possible multiplet states formed by coupling a hole in a metal-atom subshell to an unfilled valence subshell. Splittings are observed in various solids containing $3d$-series atoms. In particular, the $3s$ binding energy is split into a doublet with as much as 7.0-eV separation between the two components. The instrumental resolution is \ensuremath{\sim} 1.0 eV. $3s$ splittings are exhibited by inorganic compounds containing Mn and Fe, as well as by Fe metal, Co metal, and Ni metal. Theoretical predictions are in good agreement with experiment, provided that the effects of covalency in chemical bonding are taken into account. For Fe metal, the $3s$ splitting is identical both above and below the Curie point. The $3p$ binding energies of these solids also appear to show multiplet effects, but the interpretation of these results is less straight-forward. The $2p$ binding energies in Mn${\mathrm{F}}_{2}$ are broadened by at least 1.3 eV, and this is shown to be consistent with multiplet splitting. XPS results for gaseous monatomic Eu also indicate the presence of multiplet splittings. The two components in the $4d$ photoelectron spectrum are found to have an intensity ratio in disagreement with observed ratios for neighboring atoms with filled valence subshells. Also, the width of the $4f$ photoelectron peak above the instrumental contribution can be explained in terms of multiplet effects.
302 citations
TL;DR: In this article, the photoelectron spectrum of molecular oxygen has been studied in the range 12-28 eV with the 584 A and 304 A He lines, and the O2+ states have been measured accurately.
Abstract: The photoelectron spectrum of molecular oxygen has been studied in the range 12-28 eV with the 584 A and 304 A He lines, and the O2+ states have been measured accurately Due to the high resolution of our apparatus we have been able to observe the A2 Πu state which has been considered as absent in photoelectron spectroscopy work Its ionization energy is 17045 eV Our result is compared with spectroscopic observations of the second negative band system A2Πu → X2Πg The relative intensity of the A2Πu state is in good agreement with a recent calculation by Dixon and Hull
233 citations
05 Nov 1970
TL;DR: In this paper, a theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented, where the differential cross-section OO is of the form a = l+ /JP,(co»® ) where O Total is the total crosssection, B anisotropy parameter and O the angle between the polarization vector of the incident light and the direction of the photoelectron.
Abstract: A theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented. The differential cross-section OO is of the form a = ^ [l+ /JP ,(co»® )] where O Total is the total cross-section, B an anisotropy parameter and O the angle between the polarization vector of the incident light and the direction of the photoelectron. Expressions for O total and B in terms of internal transition dipole moments are obtained for transitions between individual rotational states of the molecule and ion, for either of Hund’s cases (a) or (b) . The formulae have been developed for central-field bases for the eigenstates of the electron before and after ionization. When rotational structure in the photoelectron spectrum is unresolved the angular distribution is independent of the choice of Hund’s case
187 citations
TL;DR: In this paper, a theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented, where the differential crosssection σΩ is of the form σ Ω = σ total 4 π [ 1 + β P 2 ( cos Θ ) ] where σtotal is the total cross-section, β an anisotropy parameter and Θ the angle between the polarization vector of the incident light and the direction of the photoelectron.
Abstract: A theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented. The differential cross-section σΩ is of the form σ Ω = σ total 4 π [ 1 + β P 2 ( cos Θ ) ] where σtotal is the total cross-section, β an anisotropy parameter and Θ the angle between the polarization vector of the incident light and the direction of the photoelectron. Expressions for σtotal and β in terms of internal transition dipole moments are obtained for transitions between individual rotational states of the molecule and ion, for either of Hund's cases (a) or (b). The formulae have been developed for central-field bases for the eigenstates of die electron before and after ionization. When rotational structure in the photoelectron spectrum is unresolved the angular distribution is independent of the choice of Hund's case.
185 citations
TL;DR: In this article, the photoelectron spectrum of benzene has been measured with high resolution, and the lowest band at 9.241 eV, which is due to ionization from a degenerate π orbital, exhibits several fundamental frequencies.
132 citations
TL;DR: The photoelectron spectrum of H2 has been measured with high resolution as mentioned in this paper, where individual rotational lines are completely resolved and it has been possible to measure some ionization energies with an accuracy of the same order of magnitude in the best spectroscopic measurements.
106 citations
01 Jan 1970-Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry
TL;DR: XPS is used to study the densities of states of the metals Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au, and also the compounds ZnS, CdCl2, and HgO and seems to be capable of giving a very good description of the general shape of the density-of-states function.
Abstract: In x-ray photoelectron spectroscopy (XPS), a sample is exposed to low energy x rays (approximately 1 keV), and the resultant photoelectrons are analyzed with high precision for kinetic energy. After correction for inelastic scattering, the measured photoelectron spectrum should reflect the valence band density of states, as well as the binding energies of several core electronic levels. All features in this spectrum will be modulated by appropriate photoelectric cross sections, and there are several types of final-state effects which could complicate the interpretation further. In comparison with ultraviolet photoelectron spectroscopy (UPS), XPS has the following advantages: (1) the effects of inelastic scattering are less pronounced and can be corrected for by using a core reference level, (2) core levels can also be used to monitor the chemical state of the sample, (3) the free electron states in the photoemission process do not introduce significant distortion of the photoelectron spectrum, and (4) the surface condition of the sample does not appear to be as critical as in UPS. XPS seems to be capable of giving a very good description of the general shape of the density-of-states function. A decided advantage of UPS at the present time, however, is approximately a fourfold higher resolution. We have used XPS to study the densities of states of the metals Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au, and also the compounds ZnS, CdCl2, and HgO. The d bands of these solids are observed to have systematic behavior with changes in atomic number, and to agree qualitatively with the results of theory and other experiments. A rigid band model is found to work reasonably well for Ir, Pt and Au. The d bands of Ag, Ir, Pt, Au and HgO are found to have a similar two-component shape.
94 citations
TL;DR: The photoelectron spectra of ethylene and ethylene-d4 have been measured using a new high-resolution spectrometer and the 584-A helium resonance line as a light source as discussed by the authors.
Abstract: The photoelectron spectra of ethylene and ethylene‐d4 have been measured using a new high‐resolution spectrometer and the 584‐A helium resonance line as a light source. Five ionization potentials have been observed for each compound. Vibrational structure associated with the transitions leading to the first and fourth ionization potentials has been resolved, and it has been possible to assign the corresponding vibrational modes. The photoelectron spectrum of neon, obtained with the 537‐A line from the same light source, is also presented.
74 citations
TL;DR: In this paper, the first two π-bands in the photoelectron spectrum of cis-ciscis cis-1, 4, 7-cyclononatriene (I, symmetry C3v) showed a Jahn-Teller split.
Abstract: The first of the two π-bands in the photoelectron spectrum of cis-cis-cis-1, 4, 7-cyclononatriene (I, symmetry C3v) shows a Jahn-Teller split. This is consistent with the prediction of molecular orbital theory that the top occupied orbitals of I are e(π) and a1(π) respectively. From the difference ϵ(e(π)) - ϵ(a1(π)) = 0.90 to 0.97 eV a value of β1,3 = −0.68 eV = 0.27 β (β = -2.5 eV) is obtained for the homoconjugative interaction of two π-orbitals in I. This value represents almost exclusively through-space interaction between the π-orbitals. Through-bond interaction (hyperconjugation) is a minor effect in I. A comparison of the photoelectron data of bicyclo [4.2.1] nonatriene with those of norbornene and cycloheptadiene shows that homoconjugation (homo-aromaticity) can only be detected by photoelectron spectroscopy if the interacting π-bonds (basis orbitals) are symmetry equivalent or have accidentally (almost) degenerate energies.
69 citations
TL;DR: In this paper, the angular distribution and intensity of photoelectrons ejected from diatomic molecules are considered and the potential information contained in rotational fine structure in molecular photoelectron spectroscopy is investigated.
Abstract: A previously developed theory of the angular distribution and intensity of photoelectrons ejected from diatomic molecules is used to consider the potential information contained in rotational fine structure in molecular photoelectron spectroscopy. It is shown that resolution of such structure would permit the evaluation of contributions corresponding to the terms in a one-centre expansion of the molecular orbital from which the photoelectron is ejected. The case of H2 is analysed in detail, and the analysis compared with that of Tully, Berry and Dalton.
TL;DR: The Fano-Mies theory of configuration interaction is applied to the photoionization of diatomic molecules, yielding an expression which gives the relative intensity of vibrational peaks in photoelectron spectra when one or more autoionizing states are in the vicinity of the excitation energy.
Abstract: Relative intensities of resolved vibrational peaks in molecular photoelectron spectra are usually assumed to be proportional to the Franck-Condon factors connecting the molecular ground state with the molecular ion final state. Recent experiments have shown, however, that the photoionization of 02 with radiation whose energy lies close to autoionizing states (either the neon resonance lines (Price I968; Natalis & Collin I968) or monochromatic excitation right at a strong autoionizing peak in the absorption spectrum Blake et al., this volume, p. 159) produces 0+ (X2JIg) with vibrational populations departing strongly from those expected from calculated Franck-Condon factors (Nicholls I968) for the ionizing transition. These anomalous vibrational intensities also occur in the photoelectron spectra of other molecules (Collin & Natalis I968 a) and complicate attempts to identify electronic energy states of the respective molecular ions (Collin & Natalis I968 b; Huber I968). In this paper the effect of autoionization on photoelectron spectra is explored by applying Fano's configuration interaction theory (Fano I96I; Fano & Cooper I965, I968) to molecular photoionization. Using the recent extensioni of the theory by Mies (I968) an expression is derived for the intensity of a vibrational peak in the photoelectron spectrum when there are one or more autoionizing Rydberg states in the vicinity of the excitation energy. The theory is more general than that developed by Bardsley (I968) for the analysis of molecular resonances but reduces to his results in the limit of a single autoionizing state. As an example (illustrative, not quantitative), the photoelectron spectra of 02 (to 02 (X2Ig)) is calculated as the excitation energy sweeps through autoionizing Rydberg states leading to O+(A2YLU).
TL;DR: In this paper, the photoelectron spectrum of NO2 has been measured with high resolution up to 27.5 eV and interpreted by use of molecular orbital theory, taking especially the vibrational structure into account.
Abstract: The photoelectron spectrum of NO2 has been measured with high resolution up to 27.5 eV and interpreted by use of molecular orbital theory, taking especially the vibrational structure into account. The electron impact energy loss spectrum has been measured with electron energy 100 eV. The spectrum above 6.5 eV has been interpreted as due to Rydberg transitions and comparison with spectroscopic measurements have been made.
TL;DR: In this article, the photoelectron spectrum excited in vanadium tetrachloride by He(I) radiation was compared with the spectrum of titanium tetrachylamide.
TL;DR: The high-resolution photoelectron spectrum of H 2 S + with adiabatic ionization engergies of 10.43, 12.76 and 14.91 eV and frequencies of 2476, 1113 and 2000 cm −1 respectively was analyzed in this article.
TL;DR: In this paper, the 584 photoelectron spectrum of borazine is given, and the ionization potentials compared with previously calculated values and with those found by an INDO calculation.
TL;DR: The photoelectron spectra of substituted pyridines and diazines are discussed in the light of the two possible explanations for the pyridine spectrum.
Abstract: Data on calculated orbital energies and experimentally measured ionization potentials of carbocyclic and heterocyclic aromatic compounds are compared and contrasted. The ordering or orbital energies and ionization potentials do not always seem to parallel one another, probably owing to either electron correlation effects, or to deviations from Koopman’s theorem. The effects on photoelectron spectra of using different light sources and analysers are discussed in relation to their bearing on the orbital orderings of aromatic compounds. The high resolution He 584 A. photoelectron spectrum of pyridine is shown to be open to two interpretations regarding the ordering of the ionization potentials of the π orbitals and the ‘nitrogen lone pair’ (n). One of the interpretations involves the three lowest pyridine ionization potentials being π (9.2 eV), π L (9.5 eV) and n (10.5 eV) whilst the other has the first three ionization potentials being the order π , n, π . The photoelectron spectra of substituted pyridines and diazines are discussed in the light of the two possible explanations for the pyridine spectrum.
TL;DR: In this paper, the photoelectron spectrum of carbon tetrafluoride was compared with X-ray emission spectra and with molecular orbital calculations, and the ionization energies at 22.2 and 25.1 eV were related to the 2t 2 and 2a 1 orbitals, respectively.
IBM1
TL;DR: In this article, the mean free path of hot electrons in Y has been determined as ∼ 10A at 7 eV above ther Fermi level EF using a new photoemission method.
TL;DR: In this article, the results of ab initio SCF-MO calculations and the photoelectron spectrum were used to analyze PF3·BH3 and showed that the bonding in PF3 is stable.
Abstract: The bonding in PF3·BH3 is discussed using the results of ab initio SCF–MO calculations and the photoelectron spectrum.
01 May 1970-Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry
TL;DR: The use of ultraviolet photoemission to determine the density of valence and conduction states is reviewed and it is suggested that k conservation becomes less important (and nondirect transitions more important) as the mass of the hole becomes larger.
Abstract: Optical density of valence and conduction states by UV photoelectric spectroscopy, outlining experimental techniques and inelastic scattering effects
TL;DR: In this article, a theoretical interpretation of molecular core binding energies as measured by X-ray photoelectron spectroscopy is given, and it is shown that simple relationships between shifts in binding energies and charge distributions can be misleading.
Abstract: A theoretical interpretation of molecular core binding energies as measured by X-ray photoelectron spectroscopy is given, and it is shown that simple relationships between “shifts” in binding energies and “charge distributions” can be misleading.
TL;DR: In this article, distribution of calculated Franck-Condon factors for autoionizing transitions are used to illustrate the way in which the vibrational structure of the photoelectron spectrum may be extended in a characteristic manner when the wavelength of the exciting radiation coincides with a resonance in the photoionization cross section of a diatomic gas.
Abstract: Distributions of calculated Franck-Condon factors for autoionizing transitions are used to illustrate the way in which the vibrational structure of the photoelectron spectrum may be extended in a characteristic manner when the wavelength of the exciting radiation coincides with a resonance in the photoionization cross section of a diatomic gas. The calculations are found to be in good agreement with resonance wavelength photoelectron spectra from 02.
TL;DR: In this paper, the high-resolution photoelectron spectrum of BF3 was used to assign the highest occupied orbital to π(e) type, rather than σ(a2′ or e′) as predicted.
Abstract: Assignment of the high-resolution photoelectron spectrum of BF3 shows that the highest occupied orbital is of π(e″) type, rather than σ(a2′ or e′) as predicted, and that one of the ionic excited states is probably distorted.
TL;DR: The A 2 Π u state of O+2 has been observed in the photoelectron spectrum of O2 and its ionization energy is 17.045 eV as mentioned in this paper.
Abstract: An alternative explanation is suggested for the weak low-ionisation-energy band in the He(I) photoelectron spectrum of Fe(hfa)3.