Electron energy loss spectroscopy (EELS) of H2O, H2S, H2Se and H2Te

Electronic excitation in H2O, H2S, H2Se and H2Te molecules has been studied by the EELS technique. Spectra of H2S and H2Se are remarkably similar with the 1b1-nd transition most intense. The intensity of the first transition 1b1-nsa1 decreases through H2O to H2Se and this transition is absent in H2Te. Transitions observed by EELS have been compared with optical absorption studies. A correlation diagram of the occupied and the excited states has been provided for these four molecules by making use of UVPES and EELS.

A novel investigation of vapor-phase charge-transfer complexes of halogens with n-donors by electron energy loss spectroscopy

Complexes of I2 with diethyl ether and triethylamine and of Br, with diethyl ether have been investigated in the vapor phase for the first time by employing electron energy loss spectroscopy. Besides the CT bands, blue-shifted vacuum-UV bands of the halogens have been assigned; the amine-I, system appears to exhibit two CT bands,associated with two different excited states of the complex.

Electron-Energy Loss Spectroscopy (Eels) Of Organic-Molecules In Vapor-Phase - Design And Fabrication Of An Indigenous Eel Spectrometer

An indigenous electron energy loss spectrometer has been designed and fabricated for the study of free molecules. The spectrometer enables the recording of low-resolution electronic spectra of molecules inthe vapour phase with ready access to the vacuum ultraviolet region. Electron energy loss spectra of aliphatic alcohols and carbonyl compounds as wellas of benzene derivatives have been recorded with the indigenous spectrometer and the electronic transitions in these molecules discussed.

Adsorption of carbon monoxide on the surfaces of polycrystalline transition metals and alloys: electron energy loss and ultraviolet photoelectron spectral studies1

Adsorption of CO has been investigated on the surfaces of polycrystalline transition metals as well as alloys by employing electron energy loss spectroscopy (eels) and ultraviolet photoelectron spectroscopy (ups). CO adsorbs on polycrystalline transition metal surfaces with a multiplicity of sites, each being associated with a characteristic CO stretching frequency; the relative intensities vary with temperature as well as coverage. Whilst at low temperatures (80- 120 K), low coordination sites are stabilized, the higher coordination sites are stabilized at higher temperatures (270-300 K). Adsorption on surfaces of polycrystalline alloys gives characteristic stretching frequencies due to the constituent metal sites. Alloying, however, causes a shift in the stretching frequencies, indicating the effect of the band structure on the nature of adsorption. The up spectra provide confirmatory evidence for the existence of separate metal sites in the alloys as well as for the high-temperature and low-temperature phases of adsorbed CO.

Study of the electronic structures of high Tc cuprate superconductors by electron energy loss and secondary electron emission spectroscopies

Energy loss spectra of superconducting YBa2Cu3O6.9' Bi1.5Pb0.5Ca2.5Sr1.5Cu3O10+δ and Tl2CaBa2Cu3O8 obtained at primary electron energies in the 170–310 eV range show features reflecting the commonalities in their electronic structures. The relative intensity of the plasmon peak shows a marked drop across the transition temperature. Secondary electron emission spectra of the cuprates also reveal some features of the electronic structure.

Electronic-Transitions In Hydrogen-Bonded Dimers Of Carboxylic-Acids In The Vapor-Phase - An Electron-Energy Loss Spectroscopic Study

An electron energy loss spectroscopic study of the formic acid dimer has shown bands centred around 7.2, 8.5, 9.8, and 11.1 eV, of which the first and the third bands are assigned to n- rc* transitions and the other two to n-n* transitions; similar transitions are found in the acetic acid dimer.

Electron energy loss spectroscopic study of Cr(CO)6, Mo(CO)6 and W(CO)6 in the vapour phase

Electron energy loss spectra (EELS) of Cr, Mo and W hexacarbonyls in the vapour phase are reported. Most of the bands observed are similar to those in optical spectra, but the two high energy transitions in the 9·8–11·2 eV region are reported here for the first time. Based on the orbital energies from the ultraviolet photoelectron spectra and the electronic transition energies from EELS and earlier optical studies, the molecular energy level schemes of these molecules are constructed.

Dielectric function and optical conductivity of TiOx (0.8

Reflection electron energy-loss spectra are reported for the family of compounds TiOx over the entire homogeneity range (0.8 < a: < 1.3). The spectra exhibit a plasmon feature on the low-energy side, while several interband transitions are prominent at higher energies. The real and imaginary parts of dielectric functions and optical conductivity for these compounds are determined using the Kramers-Kronig analysis. The results exhibit systematic behavior with varying oxygen stoichiometry.

Electron energy-loss spectroscopy study of polyatomic molecular systems under pyrolytic conditions

The technique of variable-angle, electron energy-loss spectroscopy has been used to study the electronic spectroscopy of the diketene molecule. The experiment was performed using incident electron beam energies of 25 eV and 50 eV, and at scattering angles between 10° and 90°. The energy-loss region from 2 eV to 11 eV was examined. One spin-forbidden transition has been observed at 4.36 eV and three others that are spin-allowed have been located at 5.89 eV, 6.88 eV and 7.84 eV. Based on the intensity variation of these transitions with impact energy and scattering angle, and through analogy with simpler molecules, the first three transitions are tentatively assigned to an n → π* transition, a π - σ* (3s) Rydberg transition and a π → π* transition.

Thermal decomposition of chlorodifluoromethane, chloroform, dichloromethane and chloromethane under flash-vacuum pyrolysis conditions (900-1100°C) was investigated by the technique of electron energy-loss spectroscopy, using the impact energy of 50 eV and a scattering angle of 10°. The pyrolytic reaction follows a hydrogen-chloride α-elimination pathway. The difluoromethylene radical was produced from chlorodifluoromethane pyrolysis at 900°C and identified by its X^1 A_1 → A^1B_1 band at 5.04 eV.

Finally, a number of exploratory studies have been performed. The thermal decomposition of diketene was studied under flash vacuum pressures (1-10 mTorr) and temperatures ranging from 500°C to 1000°C. The complete decomposition of the diketene molecule into two ketene molecules was achieved at 900°C. The pyrolysis of trifluoromethyl iodide molecule at 1000°C produced an electron energy-loss spectrum with several iodine-atom, sharp peaks and only a small shoulder at 8.37 eV as a possible trifluoromethyl radical feature. The electron energy-loss spectrum of trichlorobromomethane at 900°C mainly showed features from bromine atom, chlorine molecule and tetrachloroethylene. Hexachloroacetone decomposed partially at 900°C, but showed well-defined features from chlorine, carbon monoxide and tetrachloroethylene molecules. Bromodichloromethane molecule was investigated at 1000°C and produced a congested, electron energy-loss spectrum with bromine-atom, hydrogen-bromide, hydrogen-chloride and tetrachloroethylene features.