A HeI photoelectron spectroscopic study of polyunsaturated fatty acids

HeI photoelectron spectra of some unsaturated fatty acids except of docosahexaenoic acid have been observed in the gas phase for the first time, by using an infrared heating device that was developed in this laboratory. The first vertical ionization energies (I_obs) of oleic acid, linoleic acid, linolenic acid, and docosahexaenoic acid have been determined to be 8.85, 8.80, 8.77, and 8.75 eV, respectively. Several higher ionization energies have also been observed. The valence electronic structures associated with the observed ionization energies and the optimum geometries have been elucidated by ab initio calculations carried out in the present study.     

Kinetic measurements by variable-temperature photoelectron spectroscopy. The kinetic rate of the bicyclopentadiene to cyclopentadiene reaction in the medium-vacuum region

Using an appropriate reactor and variable-temperature photoelectron spectroscopy (VTPES), the kinetic rate-constant for the duration of bicyclopentadiene to cyclopentadiene is determined as approximately 1.9 s^?1 at 328°C and 0.1 torr. The study constitutes the first application of photoelectron spectroscopy to the quantitative investigation of chemical reactions. The technique might prove useful for the study of thermal decomposition reactions in the medium-vacuum region.     

Probing the molecular environment using spin-resolved photoelectron spectroscopy

Angle- and spin-resolved photoelectron spectroscopy with linearly and circularly polarized synchrotron radiation were used to study the electronic structure of model triatomic molecules, hydrogen sulfide, and carbonyl sulfide. The spin-polarization measurements of the molecular field split components of the S 2p photolines revealed a strong effect of the different molecular environments. The validity of simple atomic models to explain the results is discussed.     

Determination of transition dipole moments from time-resolved photoelectron spectroscopy

We show how to extract the energy- and coordinate dependence of dipole-moments for a neutral-to-ionic molecular transition from time-resolved photoelectron spectra. The procedure needs the potential surfaces of the neutral and the cationic state which are involved in the ionization process as an input. Given these potentials and the laser parameters it is possible to determine the functional form of the transition dipole moment from the measured time- and energy-resolved transient signals.Received: 28 February 2003, Published online: 29 April 2003PACS: 31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates - 33.80.Wz Other multiphoton processes     

The HeI photoelectron spectra of methyl-substituted 1,2,4-pentatrienes (vinylallene)

The HeI photoelectron spectra of trans-1,2,4-hexatriene(1), 4-methyl-1,2,4-pentatriene(2), 3-methyl-1,2,4-pentatriene(3), 1,3,4-hexatriene(4) and 3,4-dimethyl-1,2,4-pentatriene(5) have been obtained and interpreted. LCBO and CNDO/S calculations indicate for the highest energy orbitals a π,π,π,σ sequence as in 1,2,4-pentatriene. The effect of methyl substitution on the three π orbitals is analyzed.     

Absolute work function measurement by using photoelectron spectroscopy

Work function (WF) of a material is not only an intrinsic characteristic of bulk but also a surface property. The measurement and control of WF have been of great concern in many electronic and optical devices as the WF governs charge transfer and charge injection/collection efficiency at interfaces and emission characteristics of conventional charged particle emitters. Photoelectron spectroscopy (PES) has been mainly used to determine surface electronic structure and chemical composition. Despite the common use of this technique to measure WF, there has been a lack of discussion on how to use the PES and what to be considered to determine the absolute WF. The main contribution of this review lies in the discussion of the causes of errors when measuring WF, and provides a guide for reliable WF measurement. Along with the limitations of current measurement technology, we propose future directions for absolute WF measurement.     

Hard X-ray high kinetic energy photoelectron spectroscopy at the KMC-1 beamline at BESSY

Photoelectron spectroscopy at high kinetic energy is a research field that receives an increasing interest due to the possibility of studying bulk properties of materials and deeply buried interfaces. Recently, the hard x-ray high kinetic energy electron spectroscopy facility (HIKE) at BESSY in Berlin has become operative at the bending magnet beamline KMC-1. First results show excellent performance. Electron spectra have been recorded using x-ray energies continuously tunable between 2 keV and 12 keV. Using back-scattering conditions in the crystal monochromator very high resolution has been achieved for photon energies around 2 keV, 6 keV and 8 keV.     

Pitfalls in measuring work function using photoelectron spectroscopy

Accurate measurement of work function is essential in many areas of research and development. Despite the importance of photoelectron spectroscopy as a technique for measuring work function, there has been relatively little discussion in the literature of how to conduct accurate measurements. We review the basic technique of measuring work function using ultraviolet photoelectron spectroscopy and discuss several common sources of error related to the experimental setup. In particular, the sample-detector geometry is found to be a key experimental parameter; accurate results are only obtained when the sample is perpendicular to the electron detector. In addition, we demonstrate that photoelectron work function values correspond to the minimum work function “patch” on a non-uniform surface, in contrast to the average work function measured by other techniques, such as the Kelvin probe method.     

Determining the orientation of a chiral substrate using full-hemisphere angle-resolved photoelectron spectroscopy

Chiral interfaces and substrates are of increasing importance in the field of enantioselective chemistry. To fully understand the enantiospecific interactions between chiral adsorbate molecules and the chiral substrate, it is vital that the chiral orientation of the substrate is known. In this Letter we demonstrate that full-hemisphere angle-resolved photoemission permits straightforward identification of the orientation of a chiral surface. The technique can be applied to any solid state system for which photoemission measurements are possible.     

Analysis of the first electron-removal states of using polarization dependent angle-resolved photoelectron spectroscopy

The first electron-removal states of the layered cuprate Ba₂Cu₃O₄Cl₂ were measured using angle-resolved photoelectron spectroscopy. The symmetry and energy-momentum relations of the lowest-lying states were determined and interpreted in terms of the motion of a single hole in the two different planar Cu-O subsystems of the Cu₃O₄ plane. One subsystem is antiferromagnetic as in the undoped parent compounds of the high-temperature superconductors and the other is paramagnetic and corresponds to the strongly overdoped case. The data are compared to theoretical results on hole dynamics in two-dimensional antiferromagnetic or paramagnetic spin backgrounds. The lineshape, symmetry and dispersion of the first electron-removal states of Ba₂Cu₃O₄Cl₂ can be described in terms of Zhang-Rice singlets within a single band model. The photohole lifetime in the paramagnetic subsystem of the Cu₃O₄ plane is much smaller than with an antiferromagnetic spin background. Received 19 March 1999 and Received in final form 15 August 1999     

Probing the electronic structure of mono-nitrogen doped aluminum clusters using anion photoelectron spectroscopy

We report a photoelectron spectroscopic investigation of mono-nitrogen doped aluminum cluster anions Al_nN^- (n = 2-22). Well-resolved spectra were obtained at three photon energies (355, 266, and 193 nm), revealing the structural and electronic evolution as the number of aluminum atoms increases in the doped clusters. For small Al_nN (n < 9) clusters, the Al atoms may be viewed to be monovalent, similar to pure aluminum clusters. Even-odd alternation of the electron affinities was observed for Al_nN clusters, suggesting that neutral clusters with odd n are closed shell and those with even n are open shell. The most interesting observation is the similarity between the spectra of Al_nN^- and Al_(n-1)^- for n>12. This observation suggests that these clusters can be described as (AlN)Al_(n-1)^-, i.e., an AlN unit weakly interacting with Al_(n-1)^- clusters. The electronic and atomic structural implications of this observation are discussed.     

Vacuum UV photoelectron intensity of gaseous compounds: I. HeI spectra of simple compounds

A new method for determining absolute photoionization cross sections for gaseous compounds is proposed. In this method a mixture of a sample and a standard gas (N₂) is used in photoelectron intensity measurements so that the relative intensity of the component is obtained with respect to N₂ The relative photoelectron band area is converted to the absolute photoionization cross section on the basis of the absolute cross-section data of N₂ recently reported by Samson et al. This method has been applied to various aliphatic compounds to study the effect of alkyl substitution on photoionization cross sections of O- and N-nonbonding electrons for 584-Å radiation.     

The reaction of oxygen and water with iron films studied by X-Ray photoelectron spectroscopy

Adsorption of oxygen on iron at ambient temperature and low pressure is shown by XPS to give a chemisorbed species and the oxide, Fe₂O₃. At low temperatures a further adsorbed species is detected, similar to the nickel-oxygen system. Correction of the intensity of the oxygen signal for depth results in an oxidation curve in agreement with reported work using other techniques, i.e. oxidation is fast until about four layers of oxide are formed, at an exposure of ca. 10² L, and then proceeds slowly to about ten layers. Adsorption of water vapour produces an overlayer less than one layer in depth at an exposure of 10⁵ L. Comparison of the overlayer depths calculated from the decrease in unoxidised iron signal intensity and from the increase in oxygen intensity gives good agreement for the thick oxide film produced by oxygen adsorption, but not for the thin overlayer formed by exposure to water vapour. This suggests a difference in packing of the ions in the thin overlayer compared to the arrangement in the bulk oxide.     

Time‐resolved photoelectron spectroscopy using synchrotron radiation time structure

Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with pump–probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera‐based two‐dimensional detection of electron energy analyzers has been replaced by a new delay‐line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two‐dimensional delay‐line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump–probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station.