He(I) photoelectron spectroscopy of anions in adiponitrile solution

He(I) photoelectron spectra are reported of solutions of salts in adiponitrile in which peaks characteristic of the anions are visible; the vertical ionisation energies of these peaks are 6.91 and 7.85 (I^?), 7.6 (Br^?), 8.1 (Cl^?), 7.0 (CNS^?), 8.1 and 6.8 (NO₂^?), and 7.6eV (SO₄^2?). The salts examined were tetra-n-butyl ammonium (NO₂^?, I^?, Br^?, Cl^?, CNS^?, SO₄^2?), N-methylpyridinium I^?, trimethylphenylammonium I^?, choline I^?, methyltrioctylammonium I^? and methyltriphenylphosphonium Br^?. The relationship between these spectra and the charge transfer to solvent spectra of the anions is discussed.     

Quadrupole interaction in the solid halogens—a new (not final) look

The nuclear quadrupole interaction in the molecular solids Cl₂, Br₂ and I₂ is reanalyzed with the help of density functional calculations. Though the present formalism overestimates the intermolecular interaction responsible for the solid–gas frequency shift and the asymmetry parameter η, a consistent picture is derived by appropriate corrections. The published experimental values of η for Cl₂ and Br₂ are found to be in error.     

Cluster <Emphasis Type="Italic">ab initio</Emphasis> calculations for the C<Subscript>60</Subscript>F<Subscript>24</Subscript>, C<Subscript>60</Subscript>Cl<Subscript>24</Subscript>, and C<Subscript>60</Subscript>Br<Subscript>24</Subscript> halofullerenes

This paper reports on ab initio cluster calculations of the equilibrium geometry, electronic structure, and vibrational properties of the C₆₀, C₆₀F₂₄, C₆₀Cl₂₄, C₆₀Br₂₄ molecules.     

Harmonic Force Field and Mean Amplitudes for Gallium Tribromide and Triiodide Dimers

Harmonic force fields are developed for the Ga₂Br₆ and Ga₂I₆ molecules. The analysis confirms previous assignments of experimental frequencies. Mean amplitudes of vibration are calculated.     

Electron spectroscopy of autoionizing states of oxygen,chlorine and bromine atoms

The autoionizing atomic states are obtained in dissociation Of O₂, Cl₂ and Br₂ molecules excited by either fast neutral He atoms (O₂) or by photons with 21.217 eV energy (Cl₂, and Br₂). Tentative assignment of the autoionizing levels is given for Cl* and for Br* atoms, and a more detailed one for O* atoms.     

Calculation of absolute electron-impact ionization cross-sections of dimers and trimers

We report calculations of the electron-impact ionization cross-sections of selected dimers (homonuclear diatomic molecules) and trimers (homonuclear triatomic molecules) using a method which relies only on macroscopic quantities in conjunction with a “defect concept”. The empirically determined defect describes the deviation of the cluster (dimer, trimer) cross-sections from a simple linear dependence on the cluster size. We compare the calculated cross-sections to experimental data for the dimers S₂ and F₂ and the trimer O₃ and we present predictions for the ionization cross-sections of Br₂, I₂, C₂ and C₃ for which no experimental data are available. Lastly, we extend the method to the calculation of ionization cross-sections for the fullerenes C₆₀ and C₇₀. Received 6 December 1999 and Received in final form 10 April 2000     

Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal β″-(BEDT-TTF)4H3O[Fe(C2O4)3] · C6H4Cl2

The β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G(A^I=NH ₄ ⁺ , H₃O⁺, K⁺, Rb⁺; M^III=Fe, Cr; G = “guest” solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C₆H₄Cl₂)-containing conductor of this family, namely, β″-(BEDT-TTF)₄H₃O[Fe(C₂O₄)₃] · C₆H₄Cl₂, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) Å, b= 19.991(2) Å, c= 35.441(3) Å, β = 92.87(1)°, V= 7374(1) ų, space groupC2/c, and Z = 4. In the temperature range 0.5&;2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G crystals are analyzed.     

Luminescence of defect centres in Hg2Cl2

Abstract

Luminescence in Hg₂Cl₂, crystals excited with UV light is investigated in the spectral region 0.8–2.25 eV. Measurements are performed on as-grown samples and on samples previously exposed to UV light at RT. Six emission bands are found which depend on the concentration of the photochemical entities produced by irradiation of the crystals at RT. It is concluded that infra-red (IR) luminescence of Hg₂Cl₂ originates from crystal defects. The observed emission bands are tentatively attributed to the emission of (HgCI_xBr_3?x)^? and (HgCl_xBr_4?x)^2? complexes formed with residual Br impurities. Centres responsible for IR Hg₂Cl₂ emissions are excited: (i) via excitons of Hg₂Cl₂, (ii) via excited states of isolated Hg₂Br₂ molecules, and (iii) resonantly through the excitation bands of defect centres.     

13C NMR Chemical Shifts Substituent Effects of (E)- and (Z)-N-ethyl-N-Methylamides

Carbon-13 NMR chemical shifts of a series of (E)- and (Z)-N-ethyl-N-methylamides [RC(O)NEtMe, R=H, Me, Et, i-Pr, t-Bu, CF₃, ClCH₂, Cl₂CH, Cl₃C, BrCH₂, Br₂CH, Br₃C and ICH₂] are reported. The α-carbon and carbonyl carbon chemical shifts are correlated with the empirical α-substituent effect and Charton's electrical parameter ([sgrave]_I), respectively. The N-alkyl carbon resonances were attributed mainly to the γ- and δ-effects of R.     

Optical characteristics of plasma of I*<Subscript>2</Subscript>, Cl*<Subscript>2</Subscript>, Br*<Subscript>2</Subscript> halogen dimer barrier-discharge excilamps

Barrier-discharge excilamps operating in homonuclear chlorine, bromine, and iodine and their mixtures with inert gases have been studied. The spectral and energy characteristics of the barrier-discharge plasma have been obtained. The conditions have been determined at which the band D′ → A′ predominates in the spectra of molecules I*₂ (342 nm), Cl*₂ (257.8 nm), and Br*₂ (291 nm). The efficiencies of I₂, Cl₂, and Br₂ excilamps were found to be 1.6, 2, and 3.8%.     

Search for and study of phase transitions in some representatives of the APb2 X 5 family

Single crystals of KPb₂Cl₅, RbPb₂Cl₅, and RbPb₂Br₅ are grown and studied using optical polarization methods. The heat capacity of the crystals is investigated by differential scanning microcalorimetry, and the birefringence and the angle of rotation of the optical indicatrix are measured. The measurements are performed in the temperature range 270–640 K. It is found that KPb₂Cl₅ undergoes a first-order ferroelastic phase transition at T _0↑ = 530 K, T _0↓ = 528 K, and ΔH = 1000 ± 200 J/mol. The transition is accompanied by twinning and a change in symmetry mmm ? P2₁/c. The RbPb₂Cl₅ crystal remains monoclinic up to the melting temperature. The RbPb₂Br₅ compound belongs to the I4/mcm tetragonal modification and does not undergo structural transformations.     

Selective Stimulation of Chemical Reactions by Laser Excitation

Abstract

Among the many different applications to which lasers have been put, one of the more intriguing is their potential use in photochemistry - particularly, in inducing specific reaction pathways that are not accessible from conventional broad-band excitation. One of the first of such experiments was an attempt to use a ruby laser to carry out laser-flash photolysis of Br₂, analogous to Porter's work on I₂. Since the optical energy of the laser radiation (14,400 cm^?l) was less than the Br₂ dissociation energy, direct photodissociation was not possible; instead, excited Br₂? (³π_lu) molecules were produced, which were dissociated in subsequent collisions. The Br atoms formed in this way subsequently added to halogenated olefins such as C₄F₈ and C₄F⁷Cl.¹ The first actual laser flash-photolysis experiment, carried out in Porter's laboratory, used a Q-switched ruby laser to photodissociate dihydrophthalocyanine vapor at ca. 400°C; a multi-photon process is likely to be involved in this case.² As high-power infrared lasers became available, these were used to effect the decomposition of monia, ethyl chloride, and other molecules absorbing at 10.6 μm.^3,4 It seems clear, in retrospect, that all these reactions were essentially a laser-induced pyrolysis.     

Metal-insulator transition of solid halogens under pressure

Abstract

The band structure of solid bromine and chlorine have been calculated at different pressures. Our calculations predict that there is a closure of the gap in the direction perpendicular to the molecular planes at pressures around 150, 330 and 670 kbar for I₂, Br₂ and Cl₂ respectively.     

Time dependence of the optical emission of laser induced breakdown in gases

A detailed study of the decay of the emission intensity of the laser spark in air, Ar, Xe, Cl₂, Br₂, I₂, ICl, NO₂ and NO reveals an exponential component with one or two time constants and a non-exponential long-time component extending to 100 μsec. The emission volume at the beginning of the spark is shown to be considerably greater than the plasma core.     

Synthesis, vibrational and optical properties of a new three-layered organic-inorganic perovskite (C4H9NH3)4Pb3I4Br6

An organic-inorganic hybrid perovskite (C₄H₉NH₃)₄Pb₃I₄Br₆ was synthesized and studied by X-ray diffraction, Raman and infrared spectroscopies, optical transmission and photoluminescence. The title compound, abbreviated (C₄)₄Pb₃I₄Br₆, crystallises in a periodic two-dimensional multilayer structure with P2₁/a space group. The structure is built up from alternating inorganic and organic layers. Each inorganic layer consists of three sheets of PbX₆ (X=I, Br) octahedra. Raman and infrared spectra of the title compound were recorded in the 100-3500 and 400-4000 cm⁻¹ frequency ranges, respectively. An assignment of the observed vibration modes is reported. Optical transmission measurements, performed on thin films of (C₄)₄Pb₃I₄Br₆, revealed two absorption bands at 474 and 508 nm. Photoluminescence measurements have shown a green emission peak at 519 nm.     

Parallel trends observed in the dynamics and kinetics of the family of reactions O(3P)+XY→OX+Y (X,Y, halogen atoms) using the quasi-classical trajectory method

Summary We calculate several features in the dynamical behaviour of the reactions O(³P)+XY→OX+Y (XY=Br₂, BrCl) using the quasi-classical trajectory method. The results are compared to analogous results for the reactions O(³P)+Cl₂, I₂. The similarities observed in this homologous series of reactions indicate that the dynamics are influenced to a significant degree by the long-range repulsive forces between the reactants.     

Ion-pair states of I<Subscript>2</Subscript>, Br<Subscript>2</Subscript>, IBr,and ICl

The experimentally determined energies and rotational constants of the vibrational levels v = 0–20 of the Ion-Pair states Ω = 0⁺, Ω = 1 of the I₂, Br₂, IBr, and ICl molecules are modeled. The model used includes three diabatic states, which correlate to X⁺(3P, 1D) + Y^～(1S₀). These states are coupled by the spin-orbit interaction, which is assumed to be independent of the internuclear distance. For IBr and ICl, as well as for the ungerade states of I₂ and Br₂, satisfactory results are obtained. The model is less applicable to the gerade states of I₂ and Br₂, which is possibly results from the retainment of the asymptotic J _A J _B coupling of the angular momenta at equilibrium internuclear distances.     

Electron-attachment spectroscopy: formation and dissociation of negative ions in the fluorochloroethylenes

The formation and dissociation of negative ions in C₂Cl₄, C₂FCl₃, 1,1-C₂F₂Cl₂, 1,2-C₂F₂Cl₂ (isomeric mixture), C₂F₃Cl and C₂F₄ have been studied employing (dissociative) electron-attachment spectroscopy with nearly monoenergetic electrons in the energy range 0–15 eV. All six compounds show low-lying resonances (below 4eV) associated with various dissociation channels leading to one negative and one neutral fragment. It is found that the resonance energy increases if Cl is replaced by F. Electron affinities in the limit of the unknown excess energy are given for the radicals C₂Cl₃, C₂F₂Cl₂, C₂F₂Cl and C₂F₃. For C₂Cl₄ and C₂F₂Cl₂ long-lived parent molecular anions are observed. Only tetrafluoroethylene gives fragments by cleavage of the double bond, as a result of the perfluoro effect.     

A C2-symmetric ratiometric fluorescence and colorimetric anion sensor based on pyrrole derivative

A C₂-symmetric fluorescence and colorimetric anion sensor (1) based on pyrrole derivative was designed and synthesized according to binding site-signaling subunit approach. The compound 1 was easily prepared by reaction of pyrrole-2,5-dicarboxaldehyde with 4-nitrophenylhydrazine in ethanol (yield=78%). In DMSO, the sensor 1 exhibited a visible color change from red to brown upon exposure to anions such as AcO⁻ and F⁻; however, no obvious color changes were observed when the other tested anions (e. g. H₂PO₄⁻, Cl⁻, Br⁻ and I⁻) were added. There was a significant redshift (Δλ_max=160 nm) in UV-vis spectrum during UV-vis spectral titrations. In particular, the sensor 1 showed ratiometric fluorescence responses to anions.     

Effects of association of rhodamine 6G compounds on the IR absorption spectra

Results are reported for association with the anions Cl^–, Br^–, I^–, NO ₃ ^– , ClO ₄ ^– , GaCl ₄ ^– , and InBr ₄ ^– , as regards the IR absorption of free and bound N-H modes. The bound N-H mode is found to be characteristic of the anion and to be due to association of ion pairs joined via hydrogen bonds.