Photoionization of aqueous indole: Conduction band edge and energy gap in liquid water

Previous work on the determination of the photoionization threshold (I_sol) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H₂O solvents. In TMSi, electron scavenging by N₂O or photoconductivity measurements lead to the same I_sol value: 4.95 ± 0.1 eV. In water, I_sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I_sol; (ii) an “effective” ionic radius of indole (1.40 Å) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of ?1.2 ± 0.1 eV can be deduced for V_o, the conduction band edge of water; (iiii) from the above findings, the energy gap E_G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.     

A molecular beam study of the trapping desorption of I2 from a LiF(001) surface

Rotational, vibrational and translational Boltzmann distributions of I₂ desorbing from LiF(001) were measured using laser-induced fluorescence. The I₂ rotational temperature is lower than the surface temperature (T_S) at T_S > 300 K while the vibrational and translational temperatures are ≈T_S. An upper limit on the I₂-LiF(001) potential well depth was found to be 0.45 ± 0.03 eV.     

Order-disorder at Fe sites in SrFe2/3B″1/3O3 (B″=Mo, W, Te, U) tetragonal double perovskites

We have prepared SrFe_2/3B″_1/3O₃ (B″=Mo, U, Te, and W) double perovskites in polycrystalline form by ceramic methods. Phases with B″=U, Te and W have been studied by X-ray powder diffraction and the results have been compared with neutron diffraction data available for B″=Mo. At room temperature, the stoichiometric samples crystallize in the tetragonal crystal system (space group I4/m, Z=4). Cell parameters when B″=U, Te and W are a=5.6936(1) Å, c=8.0637(1)Å; a=5.5776(1) Å, c=7.9144(3) Å and a=5.5707(3) Å, c=7.9081(5) Å, respectively.The Mössbauer spectra at room temperature for all compounds show hyperfine parameters belonging to two Fe³⁺ sites located at lattice positions with different degrees of distortion. This is in agreement with diffraction data that indicate that the series of compounds display different degrees of Fe-site disorder, which increases in the following sequence: Mo<U<Te<W.     

X-ray absorption spectroscopy of nanostructured polyanilines

In this paper, X-ray absorption near edge spectroscopy at the nitrogen K edge (N K XANES) data of polyaniline (PANI) and its derivatives were revisited and expanded. The N K XANES spectra of PANI nanocomposites and PANI nanofibers were also investigated. The analysis of N K XANES spectra were done by the deconvolution of bands and the 1s → π* and 1s → σ* transitions were assigned by a correlation with the N K XANES spectra of smaller organic compounds. The “free” forms of PANI were dominated by bands from 397.7 eV to 399.1 eV attributed to imine and radical cation nitrogen atoms, respectively. Nitrogen bonded to phenazine-like rings can also be seen, mainly for PANI prepared at pH higher than 3.0. The spectra of nanocomposites show sharper bands than the “free” polymers as well as new bands at 398.8 eV and 405–406 eV. These new bands were assigned to phenazine-like rings and azo bonds in the structure of the polymers (polyaniline, polybenzidine, and poly(p-phenylediamine)) within the galleries of the montmorillonite clay. PANI nanofibers doped with HCl or HClO₄ show bands related to phenazine-like rings and/or dication segments of PANI, indicating that these segments are important in the formation of PANI nanofibers.     

Photoreaction of iodouracil in DNA duplex; C-I bond is cleaved via two different pathways ‘homolysis and heterolysis’

We recently found that a selective photoreaction of 5-iodouracil (^IU) occurs in 5′-(G/C)AA^IU^IU-3′ and 5′-(G/C)A^IU^IU-3′ sequences in ^IU-substituted duplex DNA. In this study, the photoreactivity of the 5′-G(A)_n^IUT-3′ sequence was examined using various ^IU-containing oligonucleotides. HPLC analysis revealed that their photoreactivity largely depends on the number of As between G and ^IU. The most efficient reactivity was observed when the number of As was two and this decreased with increasing numbers from three to five, as observed for the 5′-G(A)_n^IUT-3′ sequence. These results indicate that the G located 5′ from ^IU acts as an electron donor for ^IU, as in the photoreaction of ^BrU. In sharp contrast to the ^BrU photoreaction, ^IU was photoreactive when the number of As was zero or more than five. These results indicate that both homolytic and heterolytic pathways operate in the formation of the uracil-5-yl radical in the photoreaction of ^IU in duplex DNA. In addition, the ratio of these pathways is highly dependent on DNA sequence.     

Chemical effects on inner shells studied by photo-electron spectrometry

Fluorine 2s orbitals with ionization energiesI about 40 eV still show perceptible inter-ligand chemical effects (in molecules with shortF-F distances) in agreement with the mutual overlap integral. Other inner shells show only a chemical shift (amounting to 5 or more eV) and adjacentI values when the groundstate has positiveS.The relativistic separation of the twoI of 4f measured in 88 compounds of the elements from tantalum to uranium. The behaviour of the rare earths and hafnium is also discussed as well as the large width of 4d due to short half-life of the ionized state before a 4f electron fills the vacancy. The quantum-mechanical aspects of slowly auto-ionizing states are studied.

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Zusammenfassung In Molekülen mit besonders benachbarten Fluoratomen verursachen die Fluor-2s-Orbitale trotz ihrer Energie von ca. 40 eV entsprechend ihren Überlappungen beachtliche chemische Wechselwirkungen. Die Wechselwirkung anderer Orbitale innerer Schalen liefert dagegen nur eine chemische Verschiebung um größenordnungsmäßig 5 eV und eine Aufspaltung der Ionisierungsenergien im Falle eines positivenS-Wertes im Grundzustand.Die Spin-Bahn-Aufspaltung der beiden 4f-Ionisierungsenergien in 88 Verbindungen der Elemente Ta bis U wurde gemessen und diskutiert. Auf die große Linienbreite der 4d-Ionisierung wird eingegangen.

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Résumé Les orbitales 2s de fluor avec l'énergie d'ionisationI autour de 40 eV montrent d'effets chimiques quand les ligandes ont la distance mutuelle courte, et ils sont proportionnels aux intégrales de recouvrement. Les autres couches intérieures montrent seulement un déplacement chimique (de l'ordre de grandeur 5 eV) et des valeurs multiples deI quand l'état fondamental aS positif. La séparation d'origine relativiste des deuxI de la couche 4f est mesurée dans 88 composés des éléments entre le tantale et l'uranium. Le comportement des terres rares et de l'hafnium est discuté ainsi que la grande largeur du signal 4d, où l'état ionisé a une durée très faible parce que la position vacante rapidement est reprise par un électron 4Pitf. On étudie les états sujet à l'auto-ionisation lente de point de vue de mécanique ondulatoire.

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Dedicated to the memory of Prof. K. H. Hansen.     

The phase diagram and electrical characteristics of silver iodo-phosphate fast-ion electrolytes

The equilibrium phase diagram for the $\text{AgI}\text{Ag}{}_4\text{P}{}_2\text{O}{}_7$ system of fast-ion electrolyes is established along with the conductivity-composition relationship for polycrystalline samples. The highest conductivity compound (0.07 Ω^?1 cm^?1 at 300 K) has the composition Ag₁₆I₁₂P₂O₇. Measurements of relative permittivity and conductivity over a frequency range of 50 Hz to 100 kHz and a temperature range of 77 to 320 K on polycrystalline samples and single crystals of Ag₁₆I₁₂P₂O₇ show that the conductivity and its temperature dependence is anisotropic, with a higher conductivity along the c axis and a change in the activation energy for conduction from 0.4 eV at low temperatures to 0.14 eV above 300 K. Perpendicular to the c axis the activation energy is constant with temperature (0.28 eV). This anisotropy and a frequency dispersion in the ac conductivity between 110 to 150 K is shown to originate in the crystal structure of the material and in the distribution of Ag⁺ ions between different sites.     

Enantiomeric hybrid high-temperature multiaxial ferroelectrics with a narrow bandgap and high piezoelectricity

Ferroelectric semiconductors have sparked growing attention in the field of optoelectronics, due to their unique ferroelectric photovoltaic effect. Recently, substantial efforts have been devoted to the development of ferroelectric semiconductors, including inorganic oxides, organic-inorganic hybrids, and metal-free perovskites. Nevertheless, reports of ferroelectric semiconductors with a bandgap of less than 2 eV have been scarce. Here, in combination with the incorporation of triiodide (I₃⁻) and the introduction of chiral cations, we successfully constructed a pair of enantiomeric organic-inorganic hybrid ferroelectric semiconductors, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ (R/S-1,2-DAP = (R/S)-(–)-1,2-diaminopropane), which possess high-temperature multiaxial ferroelectric phase transition with an Aizu notation of 422F2(s) at 405 K, a narrow bandgap of 1.56 eV comparable to that of CH₃NH₃PbI₃ (∼1.5 eV), and an impressive piezoelectric response (piezoelectric coefficient, d₂₂ of 35 pC/N) on par with PVDF (polyvinylidene fluoride, 30 pC/N). With intriguing attributes, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ exhibit great potential for application of self-power polarized-light detection and piezoelectric sensors.     

Ultraviolet absorption bands of [Cs n+1 I n ]+ (n<14) clusters

Starting from the large photofragmentation cross sections recently reported for mass-selected alkali-halide clusters [1], we have obtained, for the first time, optical absorption spectra forCs _n+1 I _n ⁺ clusters in the ultraviolet charge-transfer bands. In this short report we focus on the spectra ofn=4, 6 and 13 which start to show absorption between the lowest charge-transfer band of the diatomic (ca. 3.8 eV) and that of the bulk (ca. 5.9 eV). The spectral features are analyzed for these sizes and correlated to their structures qualitatively as a preliminary model.     

Influence of synthesis condition on product formation: hydrothermal auto-oxidated synthesis of five copper halides with ratio of Cu(I)/Cu(II) in 1:1, 2:1, 3:1, 4:1 and 1:0

The hydrothermal synthesis and structural characterization of five copper iodides derived from chelated ligands, 1, 10-phenanthroline (phen), ethylenediamine (en) and 1, 3-propanediamine, are reported. Except monovalent copper compound 1 ((phen)Cu₃I₃1), other four compounds ([Cu(phen)₂I][CuI₂] 2, [Cu(phen)₂I][Cu₃I₄] 3, [Cu(en)₂][Cu₄(phen)₂I₆] 4 and [Cu(1, 3-propanediamine)₂][CuI₂]₂5) are mixed-valent Cu(I)-Cu(II) compounds by partially auto-oxidated from Cu(I). Supramolecular frameworks of these compounds can be assembled by C/N-H?I hydrogen bonds, Cu(I)-Cu(I) interaction, weak Cu-I semicoordinate interaction, C-H?π and π-π stacking interactions. It's noteworthy that we find hydrothermal synthesis under higher pH value, higher synthesis temperature and longer reaction time can obtain higher ratio of Cu(I)/Cu(II) copper iodides and organic ligand with lower steric hinderance is prone to coordinated with divalent copper to form cation unit. Finally, the fluorescent study shows 1 exhibits intense orange-red luminescence with long lifetime at 293 K and more intense emission and longer lifetime at 77 K. Moreover, the room temperature EPR spectra of above five compounds not only show the valence of copper but demonstrate the coordination environment of Cu(II) centre.     

High-Pressure Synthesis and Crystal Structure of B2S3

Two new high-pressure phases of binary boron-sulfur compounds, B₂S₃-II and B₂S₃-III, were synthesized at 3-6.2 GPa. A single crystal of B₂S₃-III was grown and the structure was determined (tetragonal, space group I4₁/a, a=16.086(2) Å, c=30.488(4) Å; V=7888(1) ų, Z=100, R=3.0% and R_w=2.8% for 3047 observed data [I>3.00σ(I)]. The structure of B₂S₃-III consists of two kinds of macrotetrahedra built up from 20 and 34 BS₄-tetrahedra. These macrotetrahedra connect each other to form an interpenetrating zincblende-type structure by sharing BS₄-tetrahedra at the corners of those. B₂S₃-III is anticipated having a rather disordered structure. From the UV-Vis diffuse reflectance spectrum, the optical band gap of B₂S₃-III was estimated to be 3.7 eV.     

Electrical and interface state density properties of polyaniline–poly-3-methyl thiophene blend/p-Si Schottky barrier diode

We have formed conjugated polymeric aniline–thiophene organic material on p-Si substrate by adding polyaniline–poly-3-methyl thiophene blend solution in acetonitrile on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward bias current–voltage (I–V) characteristics of polyaniline–poly-3-methyl thiophene blend/p-Si/Al with a barrier height value of 0.60 eV and an ideality factor value of 3.37 showed rectifying behaviour at room temperature. The polyaniline–poly-3-methyl thiophene blend/p-Si/Al Schottky barrier diode showed non-ideal I–V behaviour with the value of ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. Furthermore, Cheung's functions and modified Norde's function were used to extract the diode parameters including ideality factor, barrier height and series resistance. It has been seen that there is a good agreement between the barrier height values from all methods. However, the values of series resistance obtained from Cheung's functions is higher than the values obtained from Norde's functions. The energy distribution of interface states density, determined from forward bias current–voltage (I–V) characteristic technique at room temperature, increases exponentially with bias from 2.81 × 10¹⁶ cm^?2 eV^?1 in (0.73–E_v) eV to 1.14 × 10¹⁷ cm^?2 eV^?1 in (0.48–E_v) eV.     

Two non-centrosymmetric cubic seleno-germanates related to CsCl-type structure: Synthesis, structure, magnetic and optical properties

Two related non-centrosymmetric, cubic, quaternary chalcogenides, containing europium have been synthesized employing the molten flux method and by the reaction of europium halides with the ternary seleno-germanate, Na₆Ge₂Se₆. The reactions of Eu, Ge and Se were accomplished in a molten Na₂Se₂ flux at 800 °C for 150 h in an evacuated fused silica ampoule and yielded Na₂EuGeSe₄ (I). Similarly, Na_0.75Eu_1.625GeSe₄ (II), could be synthesized at slightly lower temperature (750 °C) with a different starting ratio of Eu, Ge, Se and Na₂Se₂. A reaction between EuCl₃ and Na₆Ge₂Se₆ in 1:2 ratio at 650 °C for 96 h in an evacuated fused silica ampoule yielded Na₂EuGeSe₄ (I), while the reaction between EuI₂ and Na₆Ge₂Se₆ in 1:1 ratio under similar conditions yielded Na_0.75Eu_1.625GeSe₄ (II). Crystal data for these compounds are as follows: I, cubic, space group I4¯3m (no. 217), a=7.3466(3), Z=2; II, cubic, space group I4¯3d (no. 220), a=14.7065(8), Z=16. The crystal structures of I and II are closely related and can be compared to a CsCl-type and its ordered superstructure, respectively. These compounds are semiconductors with optical band gaps around 2 eV. The temperature dependence of the magnetic susceptibility indicated that both compounds are paramagnetic with μ_eff.=7.6 and 7.73 μ_B, for I and II, respectively, close to the theoretical value of 7.94 μ_B for Eu²⁺. Raman spectroscopic characterization of the compounds is also reported.     

Spirocyclisation of phytoalexin 1-methoxybrassinin in the presence of Grignard reagents

The anti-cancer properties of naturally occurring (2R, 3R)-(?)-1-methoxyspirobrassinol methyl ether (I) and their synthetic amino or piperidyl analogues II inspired us to study the synthesis of new target compounds III with a C—C bond in the 2-position of indole rather than a C—N or C—O bond (I or II respectively). The goal was achieved via electrophilic-nucleophilic 3,2-difunctionalisation of 1-methoxybrassinin (IV) in the presence of bromine and the Grignard reagent leading to the formation of cis- and trans-C—C analogues of I. Finally, the anti-cancer activities of the new compounds were measured and compared with I and II in order to show the importance of a heteroatom in the 2-substituted indole on the anti-cancer activity of spirobrassinols.     

Univalent metal uranyl carbonates

Optimal procedures were developed for the synthesis of A _4?m ^I B _m ^I [UO₂(CO₃)₃]·nH₂O (A^I = Li, Na, K, Rb, Cs, NH₄, Ag, Tl; B^I = Na; m = 0?1; n = 0?6) compounds. The structure and thermal decomposition of these compounds were studied by X-ray diffraction, precision IR spectroscopy, and thermal analysis. The IR bands were assigned using mathematical simulation based on small-vibration theory. The standard enthalpies of formation of the compounds at 298.15 K were determined for the first time by reaction calorimetry.     

The Conductance- and Capacitance-Frequency Characteristics of the Rectifying Junctions Formed by Sublimation of Organic Pyronine-B on p-Type Silicon

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate has been studied. The pyronine-B has been sublimed on the top of p-Si surface. The barrier height and ideality factor values of 0.79±0.04 and 1.13±0.06 eV for this structure have been obtained from the forward bias current-voltage (I-V) characteristics. From the low capacitance-frequency (C-f) characteristics as well as conductance-frequency (G-f) characteristics, the energy distribution of the interface states and their relaxation time have been determined in the energy range of (0.53−E_v)-(0.79−E_v) eV taking into account the forward bias I-V data. The interface state density N_ss ranges from 4.93×10¹⁰ cm⁻² eV⁻¹ in (0.79−E_v) eV to 3.67×10¹³ cm⁻² eV⁻¹ in (0.53−E_v) eV. Furthermore, the relaxation ranges from 3.80×10⁻³ s in (0.53−E_v) eV to 4.21×10⁻⁴ s in (0.79−E_v) eV. It has been seen that the interface state density has an exponential rise with bias from the midgap towards the top of the valence band. The relaxation time shows a slow exponential rise with bias from the top of the valence band towards the midgap.     

Low frequency vibrational spectra of zirconocene and hafnocene sulfide [Cp2M(μ-S)]2 (MZr4+, Hf4+)

Metallocene sulfides [Cp₂M(μ-S)]₂ (I, M  Zr⁴⁺; II, M  Hf⁴⁺ and Cp = cyclopentadienyl) have been synthesized. I and II show charge transfer absorption in the visible region. FT-Raman, Raman and IR spectra of these compounds are reported for the first time. The MS stretching bands have been assigned with the help of a pre-resonance effect. The approximate normal coordinate analysis of the coordination skeleton (D_2h symmetry) aids the detailed assignment in the low frequency spectral region. Force constants of MCp and MS stretching imply that the bond order of HfL is higher than that of ZrL.     

A positron annihilation spectroscopy study of porous silicon

It was shown that the spectra of angular correlation of annihilation radiation in porous silicon are approximated well by a parabola (I _p) and two Gaussians (I _g1, I _g2). The narrow Gaussian component I _g1 is most likely due to the annihilation of localized parapositronium in pores. The full width at half maximum is on the order of 0.8 mrad, a value that corresponds to the kinetic energy of an annihilating positron-electron pair (0.079 ± 0.012 eV), and its intensity is about 1.5%. The total positronium yield in porous silicon reaches 6% in this case. The particle radius determined in the study is about 10–20 Å.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.     

Cross sections and spin polarizations of electrons elastically scattered from oriented molecules (CH3I)

Elastic differential cross sections and spin polarizations for electrons elastically scattered from CH₃I are calculated using the independent atom model. Three molecular orientations with respect to the incident electron wavevector are considered — first, the molecule is oriented randomly, second, the electron wave front and molecular bond are parallel, and third, the wavefront and the bond axis are perpendicular. It will be seen to what extent orientational averaging weakens features of the cross section and spin polarization. The calculations show that cross section and spin polarization measurements are a possible tool for determining the degree of molecular orientation. There is no degeneracy betweenI–C andC–I in cross section and spin polarization measurements. The results presented here for 200 eV and 600 eV electrons scattered by CH₃I should be considered as a case study and it should be possible to find molecules and electron energies for which even more dramatic differences between the various orientations between the molecules and the electrons can be expected.