Angle-resolved photoelectron spectroscopy of the chloro-substituted methanes

The angular distribution parameter, β, was determined for the valence orbitals (IP ′ 21.2 eV) of CCl₄, CHCl₃, CH₂Cl₂, and CH₃Cl in the 10–30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β in the photoelectron energy range of 2 to 10 eV for the non-bonding chlorine n(Cl) orbitals of these molecules was found to be similar for all n(Cl) orbitals investigated. The energy dependence of β for the σ orbitals in these molecules was similar to that observed previously for other σ orbitals. The experimental CCl₄ results were compared with theoretical CCl₄ results obtained using the Xα multiple scattering formalism. Theory predicts the existence of two strong shape resonances in each of the valence orbitals of CCl₄. The overall agreement between experiment and theory is evaluated along with the experimental evidence concerning the verification of the predicted shape resonances.     

Angle-resolved photoelectron spectroscopy of cyclopropane

The angular distribution parameter, β, determined for the valence orbitals (IP < 18 eV) of cyclopropane in the 10–30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β for photoelectron energies between, 2 and 10 eV above threshold was found to be similar to those found previously for other σ orbitals. The effects of Jahn-Teller splitting on β for the 3e′ orbital were found to be small but definitely present. The overall shape and magnitude of the β(hv) curve are, however, sufficiently for the different Jahn-Teller components that, for purposes of orbital assignments using β(hv) curves the shape and magnitude of the curves can be considered associated only with the initial state. Resonance photoionization features at a photon ener of ≈ 18 eV were observed in the 3e′ and 3a′₁ orbitals and tentatively assigned to autoionization.     

High-resolution photoelectron spectroscopy through deconvolution

A new iterative deconvolution algorithm for the development of very high resolution Hc(I)-excited photoelectron spectra of gases is presented. The algorithm accepts as input a medium-resolution spectrum and an instrument function obtained by scanning intrinsically narrow line (e.g. the Ar²P_3/2 line) under conditions identical to those used to acquire the medium resolution spectrum. The deconvolved partial spectrum of an O₂H₂O mixture is presented as a test case prior to presentation of results for three nitrogen lines. For comparison purposes directly obtained high-resolution spectra of the nitrogen lines are included. The shapes of the nitrogen lines are discussed within the framework of a one-center expansion theory of photoionization. The conditions under which deconvolution can be profitably applied are briefly discussed and an attempt is made to establish the deconvolution (contrary to still popular belief) is not in any way equivalent to curve fitting.     

Gas phase high temperature photoelectron spectroscopy: The tin monoxide molecule

The HeI photoelectron spectrum of SnO (X¹Σ⁺) has been recorded. Two bands have been observed corresponding to ionization from the 6π and 13 ionization energies of 9.98 and 10.12 eV respectively. Vibrational structure associated with the first band has been analysed to give

and D_e = 3.23 ± 0.10 eV in the SnO⁺ (X²Π) state. An assessment has been made of the ability of Hartree-Fock-Slater calculations, multiple-scattering SCF-Xα calculations and ab ini energies for the group IV diatomic monoxide molecules.     

A study of the Li1+xTi2−xO4 spinel system by diffuse-reflectance spectroscopy

The room-temperature diffuse-reflectance spectra of compositions within the Li_1+xTi_2?xO₄ spinel system ($\text{0 ≤ x ≤}\text{1}\text{3}$) show three absorption bands in the range 4000 to 48,000 cm^?1. Two high-energy absorption bands correspond to charge-transfer transitions from the oxygen-2p valence band to the titanium t_2g and σ1 conduction bands, where the σ1 band of e_g character has hybridized titanium-3d and titanium-4s parentage. The absorption band arising from promotion of electrons to the empty σ1 band does not alter with composition whereas the absorption band arising from promotion of electrons to the partially filled t_2g band narrows as the concentration of conduction electrons in the t_2g band decreases. These two high-energy absorption bands fall entirely within the ultraviolet spectral region, and the absorption edge in $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4\text{(x =}\text{1}\text{3}\text{)}$ occurs at 24,300 cm^?1 (3.02 eV). A low-energy absorption band is observed in compositions with $\text{x <}\text{1}\text{3}$ and in samples of $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4$ reduced in hydrogen at elevated temperatures. This band straddles the boundary between the visible and infrared spectral regions and shifts toward lower energy as the concentration of conduction electrons in the t_2g band decreases. The possible origins of the band are discussed; the argument is in favor of a d-d interband transition from states in the partially filled t_2g band to states in the empty σ1 band.     

The He-I photoelectron spectra of uranocene and thorocene

The bonding in unranocene and thorocene is discussed in the light of their photoelectron spectra and ionization of 5f electrons is identified.     

High-resolution HeI and HeII photoelectron spectra of the zinc and cadmium dihalide valence bands

We have recorded high-resolution HeI and HeII photoelectron spectra of the valence bands of six MX₂ compounds (M = Zn, Cd: X = Cl, Br, I) in the gas phase. Transition-state Xα SW calculations on all six compounds confirm the assignments. For the first time, we have clearly resolved the spin-orbit splitting of the II_g and II_u states in the bromide and iodide spectra: and calculated Π_u splittings, using a simple MO LCAO model and the D_xh double group, are in very good agreement with the experimental values. The relative intensities of the photoelectron peaks change markedly from HeI to HeII spectra, and Xα SW cross section calculations on ZnCl₂ predict these intensity changes rather well.     

Addition of lithium aluminium hydride to olefins catalyzed by zirconium tetrachloride: A convenient route to alkanes and 1-haloalkanes from 1-alkenes

Lithium aluminium hydride adds to olefins in the presence of zirconium tetrachloride under mild conditions. This facile reaction offers a convenient laboratory method for the hydrogenation of olefins or for the preparation of 1-haloalkanes from olefins in high yield. Unstrained internal olefins appear to be unreactive.     

Studies of UV photochemistry of psoralen and angelicin by infrared spectroscopy

The UV homodimerization reaction of psoralen and angelicin in crystalline thin layers has been investigated by means of transmission infrared and infrared ATR (attenuated total reflection) spectroscopy.

In the case of psoralen layers isoorientation was found. Dichroic ratios for several vibrational bands have been obtained. After irradiation, cis-syn photodimers were found for both psoralen and angelicin.     

Molecular spectroscopy of 2,5-distyrylpyrazine

The molecular absorption and fluorescence spectra of 2,5-distyrylpyrazine (DSP) in a Shpol'skii matrix at 4 K together with the Raman spectrum of crystalline samples at 298 K have been investigated. The transition to the lowest excited singlet state of B_u symmetry is of π—π^* character and two sites with origins at 23621 cm^?1 and 23713 cm^?1 are observed in n-tetradecane at 4 K. The DSP molecule has the same conformation in the two sites and, furthermore, the geometry of the molecule in the first excited singlet states is unchanged as compared to the ground state. The vibrational progression observed for DSP is compared with the literature data for distyrylbenzene (DSB) and slilbene.     

The lithium aluminium hydride reduction of cyclohexadienylmanganese complexes

Reduction of cyclohexadienyltricarbonylmanganese or its ring-substituted derivatives with lithium aluminium hydride leads to dihydro-derivatives. Preparative and NMR spectral information is presented and interpreted on the basis of the CH-bridged cyclohexenyl structure recently established for these products by Lamanna and Brookhart [3].     

A study of isomeric retinal triplets by low temperature spectroscopic and kinetic flash photolysis

Spectroscopic and kinetic data of triplets of all-trans retinal and several of the cis isomers obtained with frozen samples at liquid nitrogen temperature are reported. They are believed due to unisomerized triplets of the corresponding ground state isomers. Interestingly, decay of transients from 7-cis-retinal was found to be wavelength dependent.     

He I (584 Å) photoelectron spectra and photoionization cross sections of atomic chlorine and bromine

Well-resolved He I photoelectron spectra of atomic chlorine and bromine have been obtained without serious background electrons, giving rise to relative photoelectron intensities associated with differential photoionization cross sections at an angle of 90° with respect to the incident 584 Å radiation.     

A study of variant silicone rubber heart valve poppets by thermogravimetry-differential thermal analysis

Thermal analyses were used to assist in the characterization of forty selected silicone elastomer heart valve poppets which have been implanted in humans for time periods varying from 22 to 79 months. Three distinct types of thermograms were obtained which were related to the amount and general type of constituents absorbed by the poppets during implants. These results are analyzed and discussed in terms of other analytical results from solvent extraction, gas chromatographic and thin-layer chromatographic analyses.     

Oxygen species adsorbed on CeX zeolites identified by ESR spectroscopy

Two kinds of paramagnetidc O^?₂ ions have been identified by contacting molecular oxygen with CeX zeolite heat treated at 200°C in vacuo. The first O^?₂ species corresponds to the usual O^?₂ ions adsorbed on cerium oxide with the following parameters: g₁ = g_? ≈ 2.035 ± 0.002, g₂ = g₃ = g_⊥ = 2.0095 ± 0.0005 and a hyperfine pattern of six and eleven lines centred about g₃ and split by about 78 Oe, the other two components being not resolved. The second paramagnetic species of much higher intensity (larger by 2 or 3 orders of magnitude) presents rather ESR parameters and hyperfine structure. One has: g₁ = 2.0242, g₂ = 2.0208 and g₃ = 2.0112 ± 0.0003; c₁ = 24 ± 3, c₂ = 66 ± and c₃ = 12 ± 3 Oe. The six and eleven hyperfine line pattern which has been observed shows that the unpaired spin is qually distributed between two oxygen nuclei. The g tensor values are interpreted in terms of almost complete averaging of g₁ and g₂ components due to rotational motion at ?196°C about axis (3 (χ_ξ). The species is attributed to O^?₂ ion formed according to the equilibrium:

. The Ce ions are located in cationic sites SII within the zeolite supercages and are only weakly bonded to the oxygen leading to rotational motion and to case of desorption, the species reversibly disappearing by outgassing at room temperature.     

A study of ruthenium electrodes by cyclic voltammetry and X-ray emission spectroscopy

Hydrogen and oxygen adsorption properties of ruthenium surfaces are characterized and shown to be analogous to those of other noble metals. Ruthenium dissolves on potential cycles, the rate of dissolution on cycles to 1.54 V being much greater than for Pd, Rh, Ir, Pt and Au. Treatment in hot chromic acid or potential cycling to 1.3 V or above results in significant changes in the voltammogram. X-ray emission spectroscopy has demonstrated that these changes are associated with the formation and growth of an oxygen-containing layer on the ruthenium surface. Electron micrographic analysis of the surface layer included in replicas revealed that the layer is essentially amorphous. Correlations between the thickness of the layer from replica shadowing experiments and X-ray emission measurements indicated that the composition of the layer at 0.03 V was predominantly RuO with a considerable degree of non-stoichiometry. The charge on the voltammogram when oxide is present is interpreted in terms of oxidation of hydrated RuO to hydrated RuO₂ by a mechanism involving the addition and removal of protons, with corresponding changes in the valence state of the metal atom. Comparisons are made with the properties of thermally-produced RuO₂.     

Laser flash spectroscopy of iodine and iodoform

The absorption spectra and decay times of transient species produced by laser flash photolysis of iodine and iodoform solutions are reported. The results show that the primary process in the photolysis of iodoform is the formation of atomic iodine.     

Nanosecond time resolution in EPR transient nutation spectroscopy of triplet states

The dynamic behavior of transient EPR nutation signals during the first 100 ns after N₂-laser excitation or molecular triplet states in single crystals has been investigated. The onset of the signal is found to depend on the inhomogeneous width and form of the cw EPR line With phenazine (in fluorene) a time resolution of 15 ns could be demonstrated.     

High-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d orbitals in the zinc and cadmium dihalides: Ligand field splittings and intensity variations

We have recorded the high-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d levels in gas-phase MX₂ molecules (M = Zn, Cd; X = Cl, Br, I). The d level spectra split into five peaks due to the combined effect of spin-orbit splitting and ligand field splitting on the d⁹ hole state, and the spectra have been fitted to a crystal field hamiltonian involving the cubic (C₄⁰) and non-cubic (C₂⁰) parts of the field from the halide ligands. Additional peaks in some spectra are due to vibrational splitting and configuration interaction. The ¦C₂⁰¦ value increases substantially from the chloride to the iodide for both Zn and Cd. Calculations of both the crystal field (C_{2 CF}⁰) and valence (C_{2 val}⁰) parts of C₂⁰ show that the increase in observed C₂⁰ is due to the C_{2 val}⁰ term attributed to the increase in covalency from the chlorides to the iodides. Shifts in the peak position due to the 2Σ_{$\text{1}\text{2 g}$} and 1Π_{$\text{3}\text{2 g}$} states from those expected on the ligand field basis. are attributed to slight bonding effects. These effecs cause a large discrepancy between calculated and observed C₄⁰ values. The intensities of the five Zn 3d peaks change markedly from HeI- to HeII-excited spectra. The Xα SW method has been used to calculate the intensities of the σ, π and δ 3d orbitals as a function of photon energy. These calculations show dramatic changes in intensity due. for example. to shape resonances. There is usually qualitative agreement between calculated and observed intensities.     

A study of the spinel materials LiTi2O4 and Li43Ti53O4 by photoelectron spectroscopy

HeI-excited valence-band ultraviolet photoelectron spectra and MgKα-excited Ti-2p X-ray photoelectron spectra are reported for the spinel materials LiTi₂O₄ and $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4$. The presence of a Fermi edge in the ultraviolet photoelectron spectrum of LiTi₂O₄ confirms the metallic nature of this material, although the measured density of states at the Fermi energy is much lower than that expected from an independent-electron interpretation of the magnetic susceptibility. This difference is attributed to a strong interaction of the conduction electrons with the lattice vibrations. The localization of conduction electrons that occurs in the final state in the Ti-2p X-ray photoelectron spectrum of LiTi₂O₄ is attributed to a Coulomb interaction with a core hole.