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He(I) and He(II) excited photoelectron spectra of the transition metal pentachlorides MCl 5 , where M  Nb, Ta, Mo, W and Re, are reported. De

Vapour-phase He I and He II photoelectron spectra of the cyclopentadienides of indium(I) and thallium(I) are reported. The discussion concentrates on the implications of the changes in band intensity that are observed on switching from He I to He II excitation, and on the nature of the additional structure revealed in the He II spectra.

The photoelectron spectrum excited by He(I) radiation in the open-shell species. V(CO) 6 , is reported, and interpreted in general terms.

Conduction electrons introduced by doping 3% antimony into tin(IV) oxide have been shown by photoelectron spectroscopy to occupy a band whose density of states profile approximates well to that predicted by free-electron theory. The surface plasmon excitation associated with the carriers gives rise to a feature of 0.55 eV in high resolution electron energy loss spectra.

Complex core level structure is encountered in the photoelectron spectra of a wide range of narrow-band metallic oxides. The examples cited include cases where the metal atom is in an integral, formal oxidation state. The observations lend support to the view that multi-peak structure in the core photoelectron spectra of the cubic tungsten bronzes should be interpreted in terms of final-state effects rather than valence localisation in the neutral system.

HeI and Mg Kα1,2 valence band photoelectron spectra of polycrystalline samples of NbO2, MoO2 and RuO2 are reported. A marked increase is observed in the intensity of the metal 4d structure, relative to that due to oxygen 2p electrons, on changing from X-ray to UV excitation. The superior resolution of the 4d signals in the HeI spectra reveals the presence of the Fermi edge in the metallic oxides MoO2 and RuO2. In addition, the HeI spectrum of MoO2 shows a splitting of the metal 4d signal, confirming established ideas concerning the electronic structure of such materials.

Simple UV photoelectron spectrometers capable of operation with gaseous samples at temperatures up to 1000 K are described. He(I) spectra of halides of thallium, mercury, tin, lead and caesium are reported. Comparison of the spectra of the Group IVB MX 2 species with those of the TIX and HgX 2 species suggests a new assignment of the former spectra.

Valence region X-ray photoelectron spectra of the rare-earth oxides are reported and compared with spectra of the corresponding tris-dipivaloylmethide chelates. The results are interpreted with the aid of reported visible and UV absorption spectra and by recourse to the appropriate coupling model.

The He I and He II spectra of the compounds M(CO)5X and M2CO10(M = Mn, Re; X = Cl, Br, I), valence region X-ray photoelectron spectra of M2(CO)10, and the He I spectra of some related compounds are reported and discussed. From observations of intensity changes it is deduced that in M(CO)5I and Re(CO)5 Br the orbital ionisation sequence for the low ionisation potential region is e(X) < b2(M) < e(M) < a1(M—X σ bonding), but that in M(CO)5Cl and Mn(CO)5Br the sequence of e orbital ionization potentials is reversed. These assignments remove several inconsistencies which existed between earlier assignments and observations upon other compounds. Probable orbital sequences for other M(CO)5L compounds are discussed.

Two computational techniques for the deconvolution of photoelectron spectra, both based on Fourier transform theory, are described. The better method is judged to be that depending on the procedure of “band-limiting” the final result. Examples are given of its application to both core level and valence band X—PE spectra and also to UV—PE spectra.

He(II) photoelectron spectra of the Group IVB tetrachlorides MCl 4 (M = C, Si, Ge, Sn) are reported and compared with He(I) data. The discussion concentrates on the spectral intensity patterns and the nature of the additional structure revealed in the He(II) spectra.

Pronounced changes in the band intensity patterns in the photoelectron spectra of simple metal-containing molecules (HgCl 2 , TiCl 4 , VCl 4 and WCl 5 ) are observed on changing from He(I) to He(II) excitation. This can provide information concerning metal-ligand covalency.

He(I,II) and MgKα valence region photoelectron spectra of polycrystalline Ti2O3, V2O3, Cr2O3, Mn2O3, Fe2O3 and Rh2O3 have been recorded. The method of sample preparation employed gave rise to UV-PE spectra which are significantly different from those previously reported. While clear changes are observed in the spectra accompanying the semiconductor-to-metal transition of V2O3 at 150 K, there is no apparent modification of the Ti2O3 spectra accompanying its second order transition at 500 K. The remaining first row transition metal sesquioxides exhibit spectra indicative of localised 3d electrons.

The Mg K α and He(II) photoelectron spectra of polycrystalline UO 2 have been recorded. Particular care was taken to prepare a sample surface which was both representative of the bulk and as close to the ideal stoichiometry as possible. The origin of satellite structure in core-level spectra is discussed with the aid of a multi-configuration Dirac—Fock atomic calculation.

He(II) photoelectron spectra of LaCoO 3 and La 0.7 Sr 0.3 CoO 3 have been recorded. Spectra of LaCoO 3 were recorded at various temperatures in the range 77 K ⩽ T ⩽ 873 K and changes in the spectra were observed corresponding to the variation of the Co spin state in the lattice.

HeI-excited valence-band ultraviolet photoelectron spectra and MgKα-excited Ti-2p X-ray photoelectron spectra are reported for the spinel materials LiTi2O4 and Li 4 3 Ti 5 3 O 4 . The presence of a Fermi edge in the ultraviolet photoelectron spectrum of LiTi2O4 confirms the metallic nature of this material, although the measured density of states at the Fermi energy is much lower than that expected from an independent-electron interpretation of the magnetic susceptibility. This difference is attributed to a strong interaction of the conduction electrons with the lattice vibrations. The localization of conduction electrons that occurs in the final state in the Ti-2p X-ray photoelectron spectrum of LiTi2O4 is attributed to a Coulomb interaction with a core hole.

Medium resolution helium(I) photoelectron spectra of the halogen molecules Cl 2 , Br 2 and I 2 , and of the diatomic interhalogens, ICl and IBr, are reported. Vibrational fine structure is discernible in the first photoionisation bands of Cl 2 , Br 2 and ICl, while multiplet splittings are evident in the photoelectron spectra of Br 2 , I 2 , ICl and IBr. The details of the spectra are consistent with established qualitative concepts of molecular orbital theory.

The one-electron structure of the valence shell of the P4 molecule has been investigated by means of helium(I) photoelectron spectroscopy. The inferred orbital structure is in accord with the simplest expectations. Very substantial Jahn-Teller distortions are evident in the orbitally degenerate states of the molecular ion. Analogy with the symmetrical trimer, cyclopropane, casts doubt on the previous assignment of the cyclopropane photoelectron spectrum.

The photoelectron spectra excited by helium 21.2 eV radiation in the group IV halides, AB4, where A = C, Si, Ge, Sn, Ti and B = C1, Br, have been determined. The ionization potential data are discussed in terms of a simple molecular orbital description of the electronic structures.

A simple and reliable helium (I) photoelectron spectrometer, in which a retarding electrostatic field is combined with an unusually small 127° sector electrostatic analyser, is described. The overall performance of this instrument is shown to compare well with that of more elaborate spectrometers.

He(I), He(II) and valence region X-ray photoelectron spectra are reported for the Group VIA hexacarbonyls and are assigned on the basis of published molecular orbital calculations. A pronounced increase in intensity of the first photoelectron band is observed on descending the group, and multiplet structure is clearly discernible on this band in the case of W(CO)6.

Relativistic calculations have been performed for the intensities of the various photoelectron signals expected in ionisation of a partly filled 4f subshell in lanthanoid ions. The results account for discepancies found between the predictions of non-relativistic theory and the 4f photoelectron spectra of ytterbium (III)compounds.

X-Ray photoelectron spectra of the metal(III)–metal(V) oxides α-Sb2O4 and BaBiO3 are reported. Indications of ‘mixed-valency’ character in the metal core-electron spectra could be found only after careful pretreatment of the samples in situ. Under normal conditions both compounds appear to have surface phases containing just the lower oxidation state.

The He(I) photoelectron spectra of the first row transition metal tris(hexafluoroacetylacetonato) M(III) complexes are described, and the trends in the orbital energies of metal and ligand electrons are elucidated.

Theory previously developed to aid the interpretation of the photoelectron spectra of molecules containing an open shell is extended to include species with more than one open shell. The spectrum of chromocene provides a simple example.

The photoelectron spectrum excited in vanadium tetrachloride by He(I) radiation is reported and compared with the spectrum of titanium tetrachloride.

X-Ray photoelectron spectra of the metal(III)–metal(V) oxides α-Sb2O4 and BaBiO3 are reported. Indications of ‘mixed-valency’ character in the metal core-electron spectra could be found only after careful pretreatment of the samples in situ. Under normal conditions both compounds appear to have surface phases containing just the lower oxidation state.

It is shown that the presence of distinct SbIII and SbV atoms in the mixed-valency compound Cs2SbCl6 can be directly demonstrated by X-ray photoelectron spectroscopy. The surface purity of the material can be checked by supplementary studies using argon ion bombardment.

Helium-(I) and -(II) excited photoelectron spectra of the metal tetrakis(tetrahydroborates) M(BH4)4(M = Zr, Hf, or U) and the He(I) spectrum of Al(BH4)3 are reported. A simple molecular-orbital model is developed to account for features in the spectra associated with ligand ionizations. Final-state structure and cross-section variations for the outermost metal f subshells in U(BH4)4 and Hf(BH4)4 are discussed in relation to the expected atomic behaviour.

The applications of X-ray photoelectron spectroscopy in the investigation of the electronic structures of mixed-valence compounds are briefly surveyed. The experimental and theoretical problems that arise are discussed.

Helium-(I) and -(II) excited photoelectron spectra of the metal tetrakis(tetrahydroborates) M(BH4)4 (M = Zr, Hf, or U) and the He(I) spectrum of Al(BH4)3 are reported. A simple molecular-orbital model is developed to account for features in the spectra associated with ligand ionizations. Final-state structure and cross-section variations for the outermost metal f subshells in U(BH4)4 and Hf(BH4)4 are discussed in relation to the expected atomic behaviour.

Vapour phase He (II) photoelectron spectra of the thallium (I) and indium (I) halides MX (X = Cl, Br, I) are reported and compared with He (I) data. The additional structure in He (II) spectra is due largely to ionization of "inner" d electrons; the detail can be understood in terms of a weak-field perturbation of 2D5/2 and 2D 3/2 final states associated with a d9 configuration at the metal ion. However, the spectrum of TICI contains certain extra features which probably represent many-electron (or shake-up) processes.

He(I) and He(II) excited photoelectron spectra of the group IVA halides MX4 (M = Ti, Zr, Hf, X = Cl, Br, I) are reported. Ionization energy values and relative band areas are discussed using a simple molecular orbital model. It is shown that He(II) intensity patterns are of particular value in aiding the interpretation of the spectra and enable detailed conclusions about metal-ligand bonding to be inferred from the experimental data.

The ultra-violet and X-ray photoelectron spectra of the tris-hexafluoroacetylacetonato complexes of cone transition metals are reported and discussed. For many of these complexes there is either little or no literature experimental data available and, where necessary full details have been given in this thesis, both of the preparation and purification of the complexes. The gas-phase ultra-violet photoelectron spectra are discussed first, and it is shown how the spectra lead unambiguously to an energy level ordering similar to that assumed in ligand-field theory. However, in the high-spin complexes of Mn(III) and Fe(III) and in the low-spin Co(III) complex, the metal levels are observed to have ionisation energies which, for the most part, are higher than those of the least stable ligand molecular orbitals. This is in direct contradiction to the predictions of ligand-field theory and, in the case of the Co(III) complex, leads to an inversion of the trigonally split e and a1, metal d orbitals. The interpretation of the high-spin complex spectra is shown to be very difficult within the one-electron framework used for the other complexes and the ultra-violet spectra are shown to be the best guide to interpretation. The values for the ligand-field parameters so derived are similar to, though slightly larger than, those for the neutral species. The ESCA spectra of the complexes were measured and are reported in the second part of the thesis. The movements of the core levels so found are related by an expression derived by Siegbahn et al. to the charge shifts in the complexes as the metal is changed. These charge shifts are of three basic types: a polarisation of the andpi; framework of the ligand towards the metal as the metal-oxygen bond length contracts, a transfer of charge from the ligand andsigma;-system to the metal, increasing as the transition series is traversed and a charge shift from the anti-bonding metal d-orbitals back onto the andsigma;-system of the ligand as a natural consequence of its anti-bonding character. As a parallel study, the ESCA spectra of the metallocenes were also run and are reported at the end of the second part of the thesis. The charge shifts observed in these compounds show a remarkable parallel to those found in the hexafluoroacetylacetonato complexes, when the different metal charges and ligand characteristics are taken into account. These trends were shown to be in accord with other data on the metallocenes. In the last part of the thesis, the charge and orbital energy shifts deduced in the first two parts of the thesis for the hexafluoroacetylacetonato complexes are correlated with other physical measurements and a consistent picture of the bonding in these complexes shown to emerge. In particular, the shifts in ionisation energies found for many of the main bands in the ultra-violet photoelectron spectra receive a ready explanation once the ESCA data is considered. On this basis a case is made for the complementarity of the two techniques.

Marked changes in the Nb4d band in the X-ray photo-electron spectrum accompany the semiconductor-metal transition in NbO 2 . The Nb4d band progressively shifts towards the O2p band with increase in temperature.

Photoelectron spectra excited in the gas phase with He-I radiation are reported for the tetroxides, RuO4 and OsO4, and for the oxychloride species VOCl3, CrO2Cl2 and MoO2Cl2. The X-ray photoelectron spectrum of OsO4 has also been measured. The nature of the metal-oxygen bonding in these molecules, as inferred from the spectrometric data, is discussed.

The X-ray photoelectron spectra of K3Cr(CN)6 and K3Cr(NCS)6·4 H2O have been re-examined. Contrary to previous reports the form of the chromium 3s signals is in line with that observed in other chromium(III) compounds.

A study of the core-electron X-ray photoelectron (X-p.e.) spectra of the f0 compounds La2O3, LaMO3(M = Fe and Co), CeO2, and BaCeO3 is described. Results on the chelate species [La(tmhd)3] and [Ce(tmhd)4](tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) are included for comparison. Special precautions have been taken to ensure an optimal degree of surface purity of the samples. Satellite structure has been observed for the 4p, in addition to the 3d and 4d, signals in both the lanthanum(III) and cerium(IV) compounds. These satellites arc discussed in terms of coexcitations of the charge-transfer type, principally O 2p→ metal 4f transitions. In the cerium(IV) oxides the satellites are apparently due to energy-gain (representing ‘ shake-down ’) rather than energy-loss (shake-up) processes.

It is shown that the presence of distinct SbIII and SbV atoms in the mixed-valency compound Cs2SbCl6 can be directly demonstrated by X-ray photoelectron spectroscopy. The surface purity of the material can be checked by supplementary studies using argon ion bombardment.

HeI photoelectron spectra of VO2 and V2O3, measured at temperatures above and below the respective semiconductor-to-metal transition temperatures, are reported. Analysis of the vanadium 3d structure in these spectra lends strong support to the established band description of the materials.

The usefulness of certain molecular orbital theories in the prediction of molecular ionization energies is investigated. A simple Huckel treatment offers definite advantages over the more imposing CNDO method. The ab initio FSGO method of Frost is unreliable quantitatively.

Vapour-phase He(I) photoelectron spectra are reported for a variety of tris-chelates of the form ML3, where L is the enolate anion of a β-diketone (commonly hexafluoroacetylacetone) and M is one of the metals: Al, Ga, Sc, Ti, V, Cr, Co, Mn, Fe, Ru. The spectra yield information concerning the details of the metal–ligand bonding and, in the case of the transition metal complexes, information about the relative energies of the metal d and ligand orbitals.