W. R. Salaneck

Electronic structure of polypyrrole and oligomers of pyrrole

The ultraviolet photoemission and optical absorption spectra of pyrrole and polypyrrole are analyzed using the spectroscopically parametrized CNDO/S3 model. Calculated charge densities, bond orders, and orbital eigenvalues for pyrrole are compared with the extensive literature on this molecule. The densities of valence states are computed for pyrrole, oligomers of pyrrole, and an infinite planar polypyrrole chain. They provide a good description of ultraviolet valence electron photoemission spectra measured for gas‐phase pyrrole, condensed thin films of pyrrole, and thin‐film polypyrrole. The photogenerated radical cation states in polypyrrole seem to extend over four or more pyrrole units for the higher binding energy σ‐electron states but are localized on fewer units for the lowest binding energy π‐electron states. The relationship between the density of valence states and the energy band structure of polypyrrole is established. The energies of the first few dipole allowed optical absorption transitions...

Photoelectron spectroscopy of iodine‐doped polyacetylene

X‐ray and ultraviolet photoelectron spectroscopy (XPS and UPS) have been used in a study of the electronic structure of iodine‐doped polyacetylene. Core level and valence band spectra are used to assess the nature and the consequences fo the iodine doping. The spectra are compared with our previous results on pure and AsF5‐doped polyacetylene, and other published work on iodine‐doped polyacetylene.

The electronic structure of 1,2‐di(p‐tolyl)ethane and of pure and substituted [2.2]paracyclophane

Two new ’’spectroscopic’’ CNDO model parametrizations, constructed to describe the electronic excitation spectra of conjugated hydrocarbons, are utilized to analyze these spectra for the double‐benzene‐ring molecules 1,2‐di(p‐tolyl)ethane, [2.2]paracyclophane, pseudopara‐dibromo[2.2]paracyclophane, pseudopara‐dicyano[2.2]paracyclophane, and 1,1,2,2,9,9,10,10 octafluoro[2.2]paracyclophane. Our CNDO/S3 model predicts orbital eigenvalue spectra which are in quantitative (ΔE∼0.1 eV) correspondence with the ultraviolet photoemission spectra of those molecules for which they have been measured. Its predictions of the ultraviolet absorption spectra of 1,2‐di(p‐tolyl)ethane are equally quantitative, although those for the absorption spectra of the [2.2]paracyclophanes are only qualitative (ΔE≲0.3 eV). A major success of the model is its correct prediction of the observed symmetry of the radical anion ESR spectra of 1,2‐di(p‐tolyl)ethane and [2.2]‐paracyclophane: the latter result having eluded prior molecular‐orb...

Fractional ionization and the identification of intercalated species in AsF5–graphite

X‐ray photoelectron spectroscopy (XPS), x‐ray diffraction, weight uptake, and chemical analyses are correlated with basal conductivity, reflectance spectra, and other electronic properties of C8nAsF5 and its residue compounds. The chemical information shows that no more than 40% of the AsF5 equivalents oxidize the graphite, the rest merely diffusing in as neutral molecules. The XPS results show that less than 30% of the initial intercalated AsF5 is converted to AsF6−, in good accord with determinations of the fractional free carrier generation per molecule. Reactions carried out in the presence of AsF3 show that this species is not an effective reducing agent for the partially oxidized compound C8AsF5. This proves that the AsF5 removed by pumping does not originate in the reverse of the oxidation reaction.

An XPS study of intensity borrowing in core ionization of free and coordinated CO

It is shown experimentally that the pronounced satellite peaks (shakeup) seen in the core level spectra of transition metal carbonyls borrows intensity from the main line. The core level spectra of free uncoordinated molecules like CO, N2, O2, NO, and CO2 and transition metal carbonyls like Fe(CO)5 can be understood using simple intensity sum rules based on the sudden approximation. By applications of the ’’Manne–Aberg theorem,’’ we are able to explain binding energy shifts that occur upon coordination of a molecule as effects due to relaxation in the ion rather than to initial state shifts. The importance of the shakeoff continuum is addressed. Finally, a comparison of the satellite energies and positions is made to the excitation spectra of the neutral molecule. A CNDO/2–CI calculation is used to support the conclusions based upon this comparison.

Electronic structure of porphins: all valence electron molecular orbital theory and ultraviolet photoemission spectroscopy

Abstract The CNDO/S3 molecular orbital model is utilized to calculate the orbital eigenvalue spectra and ultraviolet absorption spectra of the neutral, anionic, and cationic forms of porphin, and of two reduced porphins: chlorin and phlorin. The ultraviolet photoemission spectrum of free base (i.e., neutral) porphin is measured and shown to be in good correspondence with the calculated valence electron density-of-states. The CNDO/S3 model also predicts correctly the measured relative intensities, energies, and polarizations of the components of both the first (Q) and second (B or Soret) absorptions bands.

Analysis of thin films arising from electron-, ion- and photon-beam-induced decomposition of Cr(CO)6 and Al(CH3)3

Thin films derived from ion and/or electron beam irradiation of condensed chromium hexacarbonyl (Cr(CO)6) and trimethylaluminum (Al(CH3)3) and from laser-induced pyrolytic decomposition of Al(CH3)3 are analyzed using X-ray photoelectron spectroscopy. In all cases dissociation of the metal—carbon bonds may be achieved. Deposits of metallic aluminum overcoated with oxide were obtained from laser-induced pyrolysis, whereas oxides and carbides rather than metals usually result from the processing of the condensed molecular films by electron or ion beams. Modification to the sample composition as a function of electron, ion and photon beam dosage is discussed.

Spectroscopic manifestations of charge separation in the organic solid state: a UPS study of zwitterionic glycine

Abstract Results of vapor- and condensed-phase UPS measurements and CNDO/S computations are used to address the modifications to the ordering of glycine orbitals due to charge separation upon conversion from the free molecule to the zwitterionic solid-state conformation.

Observation of time dependent relaxation effects in the photoelectron spectra of some metal carbonyls

Abstract Photoelectron measurements on transition metal carbonyls in the gas phase were made at various photon energies. Satellite peaks on the low kinetic energy side of the valence orbitals are observed and are attributed to shake up of the CO derived levels. The variation of the intensity of the shake up, relative to the main peak with the kinetic energy at which the shake up peaks are observed, provides evidence for time dependent relaxation of the final state. This data indicates that the shake up intensity is constant for kinetic energies greater than ≈20 eV.

Photoelectron spectra of chromium tetranitrosyl

Abstract The ultraviolet and X-ray-excited photoelectron spectra of Cr(NO)4 are reported. The electron binding energies, shake-up spectra, relative peak intensities and the Auger peak kinetic energies have been measured, and are compared to the spectra from gas-phase NO, from NO adsorbed on a transition metal surface, and to SCF-MS calculations. The theoretical calculations are utilized to obtain ionization energies and charge distributions, and consequently to discuss the bonding in nitrosyl complexes.