Vacuum ultraviolet photoelectron spectroscopy of atoms and molecules

For a complete study of the photoionization of atoms and molecules it is essential to make use of the technique of Photoelectron Spectroscopy and the continuum characteristics of synchrotron radiation. A brief review is given of the application of the above techniques in measuring partial photoionization cross sections and the angular distribution assymetry parameter β. Selected results are given, which are compared to theoretical values.     

High resolution X-ray photoelectron spectroscopy on nitrogen molecules

This paper summarizes recent developments for experimental and theoretical studies on core-level photoelectron spectroscopy of N₂. Analysis of experimental spectra reveals that the 1σ_g and 1σ_u core-hole states differ in energy by ~100meV and in equilibrium bond length by ~0.04pm, in agreement with ab initio predictions. The ratio of the 1σ_g and 1σ_u photoionization cross sections measured in the photon energy range up to 1 keV reveals oscillatory structure due to two-center interference, equivalent to Young’s double-slit experiment, as Cohen and Fano predicted. The experimental Auger rates for the transition to the dicationic ground state are found to be different by a factor of two for 1σ_g and 1σ_u hole states and are well reproduced by the ab initio calculations. All these findings support the delocalized picture of the core hole. Discussion is given how many-body processes involved and observations for these processes affect the observation of the localized and/or delocalized core hole.     

Relative intensities in photoelectron spectroscopy of atoms and molecules

The relative intensities of photoelectron lines is discussed. The relationship of observed intensities to angle of observation is considered as are the errors introduced by ignoring the fact that different lines may have different angular distributions. Tables of theoretical results for the angular distribution asymmetry parameter, β, are presented for incident Al K_α, Mg K_α, and Zr M_ζ radiation for all atomic ground state subshells of non-zero angular momentum. The application of these results to molecules is discussed.     

Photoelectron spectroscopy of some biological molecules

The ultraviolet photoelectron spectra (UPS) of the following biologically-active compounds are reported and/or assigned: 2,4-dinitrophenol, nicotinic acid, nicotinamide, barbituric acid, xanthine, hypoxanthine, uric acid, uracil, thymine, cytosine, adenine, guanine, β-carotene, menadione, purine and pyrimidine. The importance of UPS data is exemplified in two ways: First, by investigating the validity of the Pullman k-index approach ¹⁴ to ionization energies; and, second, by generating an experimental scale of electron-donating ability.     

Characterisation of some gold clusters by X-ray photoelectron spectroscopy

An XPS characterisation of the electronic structures of some polynuclear gold compounds is presented. The photoelectron spectra of the core levels and the valence bands are discussed in terms of the differing geometries and coordination environments in the metal clusters. The XPS analysis of “centred” and “non-centred” gold clusters shows characteristic features which operate a new distinction among these two classes of compounds.     

Near surface composition of some alloys by X-ray photoelectron spectroscopy

Chemical compositions of the alloys of CuNi (Cu_0.10Ni_0.90, Cu_0.30Ni_0.70, Cu_0.70Ni_0.30) and BiSb (Bi_0.80Sb_0.20, Bi_0.64Sb_0.34, Bi_0.55Sb_0.45) are determined by X-ray photoelectron spectroscopy. The stoichiometries are determined and are compared with the bulk compositions. Possible sources of systematic errors contributing to the results are discussed. Errors arising out of preferential etching in these alloys have been investigated. It has been inferred from such studies that the preferential etching does not enrich the surface composition with a particular component for the two systems reported here. Quantitative results of CuNi system indicate that the surface regions of the Cu_0.70Ni_0.30 alloy is Cu-rich, although no such evidence is observed in case of BiSb system.     

Characterization of some gold cluster compounds by X-Ray photoelectron spectroscopy

The charge distributions and electronic structures of some polynuclear gold compounds as determined by X-ray photoelectron Spectroscopy are discussed in terms of the differing geometries and coordination environments of these compounds.     

X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis,ESCA）.XPS属表面分析法,它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息,在各种固体材料的基础研究和实际应用中起着重要的作用.文章简要介绍了XPS仪器的工作原理和分析方法,并给出了XPS在科学研究工作中的应用实例.     

X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy，XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis，ESCA）．XPS属表面分析法，它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息，在各种固体材料的基础研究和实际应用中起着重要的作用．文章简要介绍了XPS仪器的工作原理和分析方法，并给出了XPS在科学研究工作中的应用实例．     

Valence electron binding energies of some silicon compounds from x-ray photoelectron spectroscopy

X-ray photoelectron spectra in the valence electron region were obtained for gaseous SiH₄, SiH₃CH₃, Si(CH₃)₄, SiH₃Cl, and SiF₄. The experimental ionization potentials and relative peak intensities are consistent with extended Hückel theory MO calculations. The data can be rationalized without assuming substantial participation of silicon d orbitals in the bonding of these compounds.     

X-ray photoelectron spectroscopy of core states in some magnetic virtual bound state alloys

The X-ray photoelectron spectra of the 2p levels of Mn in AgMn 20 at%, Fe in AuFe 20 at%, RhFe 25 at% and 20 at% and Co in RhCo 20 at% have been measured. The Mn and Fe spectra show features which are attributed to excitation of electrons from the 3d to higher energy states during photoemission, while the Co spectra do not.     

Auger photoelectron coincidence spectroscopy

Auger photoelectron coincidence spectroscopy (APECS) is a technique that provides us with unique information and a chance to gain insight into the significance of processes in the Auger spectra of atoms in solids. Hence it is a great aid in our understanding of the Auger process in atoms where electron correlations are strong. Despite the first demonstration of the technique more than 20 years ago, there are still very few working experiments. The reasons why, and the ways forward are discussed.     

Attosecond angle-resolved photoelectron spectroscopy

We report experiments on the characterization of a train of attosecond pulses obtained by high-harmonic generation, using mixed-color (XUV+IR) atomic two-photon ionization and electron detection on a velocity map imaging detector. We demonstrate that the relative phase of the harmonics is encoded both in the photoelectron yield and the angular distribution as a function of XUV-IR time delay, thus making the technique suitable for the detection of single attosecond pulses. The timing of the attosecond pulse with respect to the field oscillation of the driving laser critically depends on the target gas used to generate the harmonics.     

Chirped attosecond photoelectron spectroscopy

We study analytically the photoionization of a coherent superposition of electronic states and show that chirped pulses can measure attosecond time scale electron dynamics just as effectively as transform-limited attosecond pulses of the same bandwidth. The chirped pulse with a frequency-dependent phase creates the interfering photoelectron amplitudes that measure the electron dynamics. We show that at a given pump-probe time delay the differential asymmetry oscillates as a function of photoelectron energy. Our results suggest that the important parameter for attosecond science is not the pulse duration, but the bandwidth of phased radiation.     

Satellite peaks in the high energy photoelectron spectra of some small first row molecules

The gas phase high energy photoelectron spectra of CH₄, NH₃, H₂O, N₂, O₂, CO and CO₂ have been recorded, and in all cases weak satellite peaks to high binding energy of the main ionization peak are observed. These peaks are assigned to transitions to ionic states in which valence electron excitation as well as core ionization has occurred. The intensity and position of these peaks, relative to the main ionization peak have been estimated from ab initio UHF calculations on the core hole states, which in general allow assignment of the satellite peaks in terms of orbital transitions of the core hole ion.     

The determination of subshell photoionization cross-sections in some solids and gases using photoelectron spectroscopy

Relative subshell photoionization cross-sections have been measured directly for solid samples of Sodium Fluoride and Sodium Chloride by the technique