David S. Urch

Metal Kβ X-ray emission spectra of first row transition metal compounds

Abstract A large body of first row transition Kβ X-ray emission spectra are presented and the splitting of the Kβ peak into Kβ′ and Kβ1,3 is quantified by a consistent curvefitting procedure. Broad trends in the Kβ′:Kβ1,3 intensity ratio are identified and related to the oxidation state of the metal and its chemical environment. Implications for the development of X-ray emission spectroscopy as a tool for chemical speciation are considered.

The relationship between bond lengths and orbital ionisation energies for a series of aluminosilicates

Abstract Variations in the aluminium oxygen bond length of as much as 20 pm have been reported from different aluminosilicate materials. The aluminium 2s and 2p ionisation energies for a series of minerals were determined to see if these differences in bond length caused any alteration in inner orbital energies. The samples were all presented to the spectrometer (Vacuum Generators ESCA III) in powdered form. The powder was pressed into a gold mesh so as to partly fill it. The mesh was held to the end of the sample probe by double sided sellotape. The gold 4f lines from the mesh were used as a standard. It is to be hoped that since chemically similar materials were being studied in a physically similar manner that this method of standi sation might be satisfactory. The results for both Al 2p and Al 2s orbitals showed an increase in binding energy of about 0.5 e.v. in going from samples such as microcline and albite (AlO, 175 Pm) to α-alumina and grossularite (AlO, 192, 195 pm). It therefore seems reasonable to conclude that a correlation between bond length and orbital ionisation energies does exist.

The unsuitability of gold as a standard for non-conducting samples in X-ray photoelectron spectroscopy

Abstract The bombardment of non-conducting substances with X-rays causes charging which alters the kinetic energies of the ejected photoelectrons. Some means of

Boron K alpha X-ray emission and the electronic structure of boron compounds: coordination and resonance emission

The boron Kα X-ray emission spectra from a series of borates and other compounds has been measured. The main peak profile is determined by the participation of B 2p orbitals in different molecular orbitals and thus reflects the electronic structure in the neighbourhood of the boron atom. Low energy satellites are observed when boron is in combination with other first row elements: the energy separation of the satellite from the main peak can be used to identify the ligand atom. A high energy satellite peak (at the B K absorption edge) is also sometimes observed. The presence of this resonance peak can be correlated with trigonal coordination about the boron.

Soft X-ray spectroscopy (20-150 Å) with a conventional X-ray spectrometer

Soft X-ray spectroscopy can be carried out in commercially available spectrometers if the following simple changes are made:(1) an open window gas-discharge X-ray tube (e.g. CGR Elent-10) is used for the excitation of characteristic X-rays,(2) large 2d spacing crystals or multilayers are used to disperse the X-rays and(3) a one micron (or thinner) window is used in the proportional counter.Examples are given of Al, Si, P and S L X-ray and Be, B, C and N K X-ray spectra, measured on a Philips PW 1410 spectrometer. Results using multilayers and organic ester crystals (octadecyl maleate-OHM, 2d 6.25 nm and octadecyl adipate-OAO, 2d 9.12 nm) are compared; the former shows much greater intensity, the latter much better resolution.

Chemical effects in the X-ray emission (F Kα) and X-ray photoelectron spectra of alkali-metal and alkaline-earth-metal fluorides

X-Ray emission (XE) and both core and valence-band X-ray photoelectron (XP) spectra have been measured for LiF, NaF, KF, BeF2, MgF2, CaF2, SrF2 and BaF2. Both the F 1s ionisation energies and the F Kα X-ray energies decrease as the cation atomic number increases within a group of the Periodic Table. Knowledge of the F 1s binding energy enabled the valence-band XP spectra to be aligned on a common energy scale for direct comparison with the F Kα peak profile. Both the XE and XP spectra showed broader bands for the lighter cations, which for Li, Be, Mg and Ca could be resolved into two distinct components. Symmetric broadening of the valence-band peaks was rationalized as due to anion–anion interaction whilst additional structure on the low (kinetic) energy side and low (X-ray) energy side of the main XP and XE peaks was related to covalent character in the cation–fluoride bond. Differences in the relative intensities of these components for XE (reflecting F 2p character only) and the XP spectra were ascribed to the presence of F 2s and possibly cation s character in the more tightly bound orbitals of the valence band. Measurement of the BeKα and Mg Kβ XE spectra gave a direct indication of the covalent nature of the bonding in BeF2 and MgF2.

The Use of HAM/3 in Interpreting the Oxygen K Emission Spectrum from Oxalate and Carbonate Anions

Abstract Molecular x-ray emission spectroscopy (XES), as other valence electron spectroscopic techniques, often yields spectra which may consist of no more than a few close lying or overlapping broad bands representing a relatively large number of active transitions. Oxygen K emission spectra often fall into this category even if the instrumental resolution is quite excellent (0.1-0.5 eV) simply because the natural halfwidths of the transitions may be of the order of 0.5 to 2 cV, and the transitions themselves may be very close (0.1 to 0.5 eV) to each other. Thus, deciphering a deceptively simple spectrum may be a difficult task. Aside from the correlation of the XES results with photoelectron data, it is highly desirable to have on hand reliable but inexpensive theoretical methods of calculating the eigenvalues and eigenvectors associated with the various molecular orbitals. In this report we show that HAM/3 developed by isbrink and coworkers(l) is, indeed, a useful and very inexpensive method for interp...

The nature of the phosphorus-metal bond in triphenylphosphine—transition metal complexes (Pd[P(C6H5)3]4, Rh(CO)Cl[P(C6H5)3]2 and Ir(CO)Cl[P(C6H5)3]2. A direct determination of the importance of P3d and PC σ∗ orbitals in ‘back-bonding’ by X-ray emission spectroscopy

Abstract X-ray emission spectroscopy has been used to establish that phosphorus makes little or no use of its 3d orbitals in bonding in triphenylphosphine or in triphenylphosphine complexes. In contrast, direct evidence is presented for the formation of new bonds between the transition metal d orbitals and the phosphorus-carbon σ bonds.

The metal–ligand bond in tropolone complexes of aluminium and silicon. A study based on X-ray emission and X-ray photoelectron spectra

X-Ray photoelectron and X-ray emission (Al-Kβ1,3, Si-Kβ1,3, O-Kα) spectra from the tris(‘tropolonate’) complexes [Al(C7H5O2)3] and [Si(C7H5O2)3][PF6] have been measured. These spectra show that the bond between the ligand and aluminium or silicon has both σ and π components. This observation is rationalised using simple molecular orbital theory.

Photoelectron and X-ray spectroscopy of minerals. Part 1.—Electronic structure of forsterite (magnesium orthosilicate)

X-ray emission (Si Kβ1,3, Si L2,3M, Mg Kβ1,3 and O Kα) and X-ray photoelectron spectra are presented for forsterite (Mg2SiO4) and aligned on a common energy scale using core ionisation energies. The energies and relative intensities of peaks in these spectra are discussed in terms of possible theoretical models for SiO4–4: ab initio, Xα etc. The magnesium Kβ X-ray emission peak profile and position relative to oxygen Kα shows that the O—Mg bond is more ionic than O—Si. The spatial position of magnesium ions relative to silicate anions would appear to facilitate σ—π mixing, i.e. the mixing of orbitals which to a first approximation could be regarded as either O—Si bonding or oxygen lone pairs.