Harmonic dynamical behaviour of thallous halides

Harmonic dynamical behaviour of thallous halides (TlCl and TlBr) have been studied using the new van der Waals three-body force shell model (VTSM), which incorporates the effects of the van der Waals interaction along with long-range Coulomb interactions, three-body interactions and short-range second neighbour interactions in the framework of rigid shell model (RSM). Phonon dispersion curves (PDC), variations of Debye temperature with absolute temperature and phonon density of state (PDS) curves have been reported for thallous halides using VTSM. Comparison of experimental values with those of VTSM and TSM are also reported in the paper and a good agreement between experimental and VTSM values has been found, from which it may be inferred that the incorporation of van der Waals interactions is essential for the complete harmonic dynamical behaviour of thallous halides.     

The vapour-phase ultra-violet photoelectron spectroscopy of metal halides at elevated temperatures

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 MX₂ species with those of the TIX and HgX₂ species suggests a new assignment of the former spectra.     

Angle-resolved ultraviolet photoelectron spectroscopy of expitaxial films of vanadyl-phthalocyanine grown on alkali halides

The molecular orientation of Vanadyl-Phthalocyanine (VOPc) grown on alkali halides was studied by Angle-Resolved Ultraviolet Photoelectron Spectroscopy (ARUPS). To avoid charging up of the specimen during ARUPS measurment, thin epitaxial films of alkali halides grown on GaAs (0 0 1) were used as substrates. Photoelectrons emitted from the highest occupied molecular orbital band of VOPc showed strong angular distribution leading to the conclusion that the molecules stay almost parallel on the surface. This was in accordance with the expectation based on the reflection high-energy electron diffraction analysis of the film.     

The photoelectron spectra of gaseous silver halides

Ionization potentials have been determined for gaseous AgCl, AgBr and AgI using He(I) photoelectron spectroscopy. The solids were vaporized directly into the photon beam from a heated substrate. Molecular orbitals were assigned to observed spectral bands based upon simple molecular orbital arguments, band intensity relationships and observed spin—orbital splitting. The spectra of the gaseous silver halides are more complex than those of other diatomic halides as a result of Ag(d)-X(π) interactions which occur in these molecules.     

The photoelectron spectra of gaseous alkali halides

The He I photoelectron spectra of the gaseous forms of CsF, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, NaI, KI, RbI, and CsI have been obtaine using a high-temperature spectrometer equipped with an internally-located, laser-beam heated sample oven. The spectral bands have been assigned molecul origins by use of MO calculations, spin—orbital splitting considerations, band intensity relations, polymer formation tendencies, and mass spectromet     

Radiative transition of two indirect excitons to direct exciton in thallous halides

Weak emission lines are observed at the energies far lower than the energies of edge emissions in TlCl and TlBr. They are explained as due to the radiative decay of two indirect X⁺₆ × R^?₆ excitons, both at the same M-point, by leaving one direct X⁺₆ × X^?₆ excitons through zero-phonon process.     

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.     

EUV and soft X-ray photoelectron spectroscopy of isolated atoms and molecules using single-order laser high-harmonics at 42 eV and 91 eV

Photoelectron spectroscopy of isolated atoms and molecules using single-order high-harmonics of Ti:Sapphire laser pulses (800 nm, 12 fs/30 fs) is demonstrated. Dielectric multilayer mirrors, SiC/Mg and Mo/Si, are used to isolate the 27th (42 eV) and 59th (91 eV) order harmonics, respectively. The obtained harmonics are characterized by valence and inner-shell photoelectron spectroscopy of Xe. The applications to two-color two-photon ionization of He and pump-probe spectroscopy of ultrafast photodissociation of Br₂, Br₂(C¹Π_u) → Br(²P_3/2) + Br(²P_3/2), are presented.     

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．     

The photoelectron and absorption spectra of allyl halides

The ultraviolet photoelectron spectra (5–20 eV) absorption spectra (1400–2500 Å) of allyl C₃H₅X (X = F, Cl, Br, I) have been measured. The ionisation potentials between 5–16 eV are determined and the type of orbital is interpreted with the aid of the vibration pattern and the band form.From these spectra several conclusions can be drawn concerning the iodide: (1) the ionisation potential of the π_C_C system of allyl iodide is lower than expected when compared to the ionisation potential of the corresponding band of the other halides. (2) The splitting of its np lone pair photoelectron bands is not in accordance with the expected splitting associated with spin-orbit coupling. (3) One of the two components of the lone pair bands has been broadened. These observations can be explained by a through-space interaction of one of the iodine “lone pairs” with the π-system.     

Electronic structure of copper halides CuI and CuCl: A comparative X-Ray photoelectron and absorption spectroscopy study

The energy distributions of the occupied and unoccupied electronic states for copper halides CuCl and CuI have been investigated using X-ray photoemission and absorption spectroscopy with a highenergy resolution on the equipment of the Russian-German beamline for outlet and monochromatization of synchrotron radiation from the electron storage ring BESSY II. A quasi-molecular analysis of the obtained experimental spectra has revealed that there is a fundamental similarity of the energy structures of the valence band and the conduction band of copper halides CuX (X = Cl, I) due to the identical atomic structure of the studied compounds. The differences in the positions of individual energy subbands in the valence band and the conduction band of CuX and in their intensities in the spectra are associated with different degrees of hybridization of the Cu 3d, 4s and X(n + 1)s, np valence states, as well as with different sizes of structural units (CuCl₄ and CuI₄ quasi-molecules) of the studied crystals.     

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.     

Molecular photoelectron spectroscopy at 132.3 eV: N2, CO,C2H4 and O2

The molecular photoelectron spectra of gaseous N₂, CO, C₂H₄ and O₂ were obtained using yttrium Mζ X-rays (132.3 eV). Comparison with spectra taken with MgKα₁₂ X-rays (1253.6 eV) showed the molecular orbitals derived from atomic 2p orbitals to be emphasized in the YMζ spectra. Orbital compositions were confirmed in N₂ and CO, and the presence of several peaks was either better established or detected for the first time (e.g., a ²Π_u state at 23.5 eV in O₂⁺) in C₂H₄ and O₂. The relative cross-section predictions of Rabalais et al. were tested by these spectra. The theoretical values, which were based on ground-state wavefunctions and plane-wave (PW) or OPW continuum states, were found to agree qualitatively with experiment, establishing that this level of theory has diagnostic value. Quantitative agreement is lacking, however. The potential application of 132.3 eV X-rays to the study of photoemission from adsorbed molecules on surfaces is emphasized.     

Higher-order spin-orbit interaction in photoelectron spectra of mercury halides

Spin-orbit interaction is introduced into the semi-empirical Extended Hückel MO scheme by adding the spin-orbit interaction operator to the effective     

The reflection spectra of cuprous halides in the 4.5–7.5 eV range

The reflection spectra of cuprous halides have been measured on cleaved samples at various temperatures from 300 K up to 6 K. The experimental device is improved by a minicomputer based data acquisition system. The appearance of structures at low temperature, the evolution of the spectra versus temperatures permit us to interprete some experimental features in terms of a band structure scheme where the valence bands are calculated in the tight binding approximation, the spin orbit splitting being introduced as a perturbation.     

Interpretative methods in photoelectron spectroscopy

Experimental carbon and nitrogen core electron binding energies measured by high energy photoelectron spectroscopy are reported together with ab initio and semi-empirical molecular orbital studies for a series of organic pseudohalides. The derived wavefunctions are used in a discussion of molecular potential models which are employed in the interpretation of core photoelectron spectra. The application of localized wavefunctions in this context is described.