Speeds of sound and isentropic compressibilities of (n-alkoxyethanols + toluene) at T = 298.15 K

Speeds of sound u at the temperature 298.15 K for six ( n -alkoxyethanol  +  toluene) were measured over the whole composition range. The n -alkoxyethanols were 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and 2-(2-butoxyethoxy)ethanol. Excess molar volumes V_m^E atT =  298.15 K were also measured for the mixtures of toluene and 2-methoxyethanol, 2-ethoxyethanol, or 2-butoxyethanol over the whole composition range. The speed of sound values were combined with excess molar volumes to obtain values for the product K_{S, m} of the molar volume and the isentropic compressibilityκ_S , and the corresponding excess quantities K_S,m^E were also calculated. The K_S,m^E curves are sigmoid for all mixtures. The deviations of the speeds of soundu^D from their values u^id in an ideal mixture were obtained for all measured mole fractions. These values are compared with the mixing function δu calculated in the paper. The behaviour ofu , u^D, δu, and K_S,m^E as a function of composition and number of carbon atoms in the aliphatic chain of the alkoxyethanol is discussed. Also, theoretical values of the molar isentropic compressibility K_S,m and speed of sound u were calculated using the Prigogine-Flory-Patterson theory with a van der Waals potential energy model and the results compared with experimental data.     

Analysis of a quasi-reversible two-electron cyclic voltammetric wave for an organometallic ir(III)/ir(I) couple at platinum and mercury electrodes

^*CpIr(η-C₆Me₆)^2+/0 (^*Cpη⁵-C₅Me₅) displays Nernstian two-electron voltammetry at a Hg electrode, but quasi-reversible charge transfer kinetics at solid electrodes. Cyclic voltammetry (CV) peak shapes and separations change drastically from one solvent to another at Pt, ΔE_p values being as small as 170 mV in acetone and as large as 350 mV in CH₃CN (v = 0.03 V/s). These variations arise from changes in the relative E° values of the one-electron Ir(III)/Ir(II) and Ir(II)/Ir(I) couples, and from changes in charge-transfer rates. It is concluded that the Ir(II)/Ir(I) couple has a significantly lower charge-transfer rate than the Ir(III)/Ir(II) couple at platinum electrodes. The sensitivity of the CV curves to the relative E° values allows the approximate determination of the individual E° values for each one-electron process. In contrast, Nernstian conditions allow only the average of the two one-electron E° potentials to be determined. Solvents with higher solvating power are shown to facilitate the thermodynamics of the two-electron transfer process by moving E°₂ positive with respect to E°₁. Possible reasons for the abnormally slow charge transfer rates at Pt electrodes are discussed.     

Polarized infrared reflection spectra of AlCl3·6H2O single crystals

Polarized i.r. reflection spectra of AlCl₃·6H₂O single crystals are presented in the range 40–4000 cm⁻¹. The oscillator parameters and the transverse and longitudinal optical phonon frequencies are calculated by means of the classical oscillator fit method. The TO/LO splittings and frequency shifts of the water bands in A_2u and E_u species are discussed in terms of hydrogen bonds, the metal—water interaction and the orientation of the H₂O molecules in the lattice.     

New details in the polarized spectrum of naphthalene by means of linear dichroism studies in oriented polymer matrices

Linear dichroism (LD) spectra are presented for naphthalene oriented in stretched polyethylene and polypropylene matrices at 77 K and 296 K. From the calculated spectrum LD(λ)/A(λ), where A(λ) is the corrected absorbance spectrum of the sample by unpolarized light, orientational parameters are calculated and component spectra, 235–315 nm, are resolved corresponding to polarization parallel to the long (B_3u = x) and the short (B_2u = y) axes in the molecular plane (D_2h). The orientational parameters indicate different orientational mechanisms in polyethylene and polypropylene, but the resolving procedure yields mainly identical component spectra. It is suggested that the polarization (B_3u) predominating in the 245–275 nm region isdue to a B_1g vibronic perturbation of the ¹B_2u state.     

The vibrational spectra of molecular crystals of ferrocene,ruthenocene, osmocene and nickelocene

Studies are presented of the infrared spectra (3200–400 cm^?1) of monocrystal films of Fe (C₅H₅)₂ Ru(C₅H₅)₂, Os(C₅H₅)₂ using polarized radiation, and of the laser-Raman spectra of solid samples of these compounds in the temperature range +20° to ?190°C. The samples were prepared by slow cooling of the melts. The infrared spectra of solid films of Ni(C₅H₅)₂ made by deposition on a cold window, were also recorded. Assignments of the fundamental vibrational frequencies of these molecules are given. The fundamental modes of vibrations which are forbidden by symmetry appear in the spectra of the solid state. The vibrations of species E_1u and E_2u showed definite site group splitting. At the point of phase transition in the IR spectrum of Fe(C₅H₅)₂ factor-group splitting to give 3–4 components for bands of species A_1u and A_2u and 6–8 components for bands of species e_1u and E_2u was observed. Factor-group analysis is more consistent with C₁ site symmetry of the low-temperature phase of the crystal of ferrocene than C_i, as was proposed earlier.     

Emission spectra of supersonically cooled dimethyldiacetylene cations

The ā²E_u → X?²E_g emission spectra of 2,4-hexadiyne (dimethyldiacetylene) cation and its d₃- and d₆-deuterated analogues were excited by electron impact on a seeded helium supersonic free jet. Vibrational analyses are made and vibrational frequencies in both states are inferred to ±1 cm^-1. Spin-orbit splittings are observed especially in degenerate overtone bands. The observed rotational contours allow a partial rotational analysis.     

Study of Intermolecular Interaction in Dimethylsulphoxide + 1-Alkanols (1-Butanol, 1-Hexanol, 1-Octanol) At 303.15 K

Abstract

The ultrasonic velocity, u, viscosity, η, and density, ρ of dimethylsulphoxide (DMSO), 1-butanol, 1-hexanol, 1-octanol, and of their binary mixtures, where DMSO is common component, have been measured at 303.15 K. From the experimental data, excess isentropic compressibility, K ^E _s, excess intermolecular free length, L^E _f, excess velocity, u ^E, excess acoustic impedance, Z ^E, excess viscosity, η^E, excess free energy of activation of viscous flow, G?^E, and excess rheochore, [R ^E] have been calculated. The behaviours of excess functions with composition of the mixtures suggest that the structure-breaking effect dominates over the interaction effect between the component molecules. Furthermore, the experimental values of u and η were fitted by empirical equations stating their dependence on composition of the mixtures. The experimental values of u have been compared with those calculated by using Nomoto and Van Dael relations.     

SINGLET-TRIPLET SPIN TRANSITION IN AN IRON(II) COMPLEX OF 1,10-PHENANTHROLINE-2-CARBOTHIOAMIDE

Abstract

The ⁵⁷Fe Mössbauer effect for the solid complex FeLCl₂·H₂O (L=10-phenanthroline-2-carbothioamide) has been studied between 4.2°K and 298°K. Two overlapping doublets (I and II) are observed, their relative intensity being strongly temperature dependent. The doublets are characterized by δE_Q(I)=0.53 mm sec^?1, δ^IS(I)=+ 0.22 mm sec^?1 and δE_Q(II)=1.33 mm sec^?1, δ^IS(II)=+0.23 mm sec^?1 at 4.2°K. In conjunction with magnetic data, the Mössbauer spectra are interpreted in terms of a singlet-triplet spin transition of the central iron(II) ion. In an applied magnetic field at 4.2°K, H_int=0, V_ZZ(I)>0, and V_ZZ(II)>0. The results are consistent with optical electronic and infrared vibrational spectra.     

Magnetic circular dichroism and absorption spectra of the mononegative and dinegative ions of [16] annulene

The magnetic circular dichroism (MCD) and absorption spectra of the mononegative and dinegative ions of [16] annulene have been measured in the 16000–30000 cm^?1 region. The results are interpreted using a PPP molecular orbital calculation. It is found that the D_4h symmetry, using Slater type atomic orbitals excellent agreement between experiment and calculations is obtained. The excited ²E_g and ¹E_u states of the mono- and dinegative ions have experimental averaged angular monomenta of 1.0 h and 2.3 h respectively and we conclude to planar ring structures for the ions. Variations in the parameters for the PPP calculations, i.e. B, do not influence the MCD values to any great extent.In addition, from temperature dependent measurements between 20°C and ?150°C, the thermodynamic parameters ΔH and ΔS for the equilibrium observed between molecule and ions in solution have been determined.     

Thermodynamic Investigation of Dimethyl Sulfoxide Binary Mixtures at 293.15 and 313.15 K

Densities (ρ), speeds of sound (u), and isentropic compressibilities (k _S) of binary mixtures of dimethyl sulfoxide (DMSO) with water, methanol, ethanol, 1-propanol, 2-propanol, acetone and cyclohexanone have been measured over the entire composition range at 293.15 and 313.15 K. The excess molar volumes (V ^E), the deviations in speed of sound (u ^E) and the deviations in isentropic compressibility (k _S ^E) have been determined. The V ^E, u ^E and k _S ^E values were fitted by the Redlich-Kister polynomial equation and the A _k coefficients as well as the standard deviations (d) between the calculated and experimental values have been derived. The results obtained are discussed from the viewpoint of the existence of interactions between the components of the binary mixtures.     

A simple reliable approximation for isotropic intermolecular forces. A critical test using HH(3Σu+) as a model

A simple semi-empirical approximation for the exchange energy (E_x), coupled with a tractable representation of the Coulomb energy (E_C), has been found to yield very accurate results for the isotropic part of the interaction energy (E_int = E_x + E_C) between two closed shell systems. The expression for E_int is based on the knowledge of the first order Coulomb energy and the first three terms in the asymptotic long range expansion of the second order Coulomb energy for the interaction and contains but one adjustable parameter which occurs in E_x. The usefulness of this approach for evaluating E_int is tested critically by using the non-bonded H(1s)H(1s) (³Σ_u⁺) interaction as a model (accurate values of the total interaction energy, the exchange energy, and various orders of Coulomb energies, are available for a wide range of R for this system). The results obtained for both E_int and (dE_int/dR) are inremarkable agreement with the exact results of Kotos and Wolniewicz for R > 3 a_o. Since the law of corresponding states for inert gas pairs holds equally well for the HH(³Σ_u⁺) interaction, our analysis of this simple system yields valuable information on the reliability of the approach for other van der Waals dimers.     

The predissociation of Li2 b3Πu by a3Σ+u

⁶Li₂ 1³Δ_g(F₁) → b³Π_u(F₁v = 0–11) rotationally resolved fluorescence spectra are recorded following perturbation-facilitated optical—optical double resonance excitation of 1³Δ_g via spin—orbit mixed A¹Σ⁺_u ∼ b³Π_u(F₁e) intermediate levels. The f-symmetry Λ-components of b³Π_u(F₁) are broadened above the 0.05 cm⁻¹ detection threshold owing to predissociation by the vibrational continuum of the a³Σ⁺_u state. The observed v = 0–11, N = 31f level widths were used to determine the potential energy curve for the Li₂ a³Σ⁺_u state in the region 2.35 < R < 2.60 Å and 11200 < E < 14900 cm⁻¹ (relative to E = 0 at the minimum of X¹Σ⁺_g). The a³Σ⁺_u ∼ b³Π_u curve crossing is at R = 2.57 Å and E = 11246 cm⁻¹ and the electronic part of the − BN·LL-uncoupling matrix element is 〈b Π¦L⁺ ¦aΣ〉 = 1.216H at an R-centroid Rv_bϵ_a = 2.61Å.     

Inelastic neutron scattering study of low frequency motions in [Co(C5H5)2+] and [Cr(C6 H62+] intercalated in the MnPS3 layered compound

The incoherent inelastic neutron scattering (INS) spectra of Mn_0.84PS₃[Co(C₅H₅)₂] _0.32 and Mn_0.86 PS₃[Cr(C₆H₆)₂]_0.28 compounds at 10 K have been investigated within the frequency ranges 0–80 cm^?1 (E₀ = 12.5 meV) and 0–360 cm^?1 (E₀ = 50 meV). Also, infrared and Raman spectra (0–400 cm^?1 of Cr(C₆H₆)₂I at various temperatures have been obtained for the first time. From a comparison of far infrared, low frequency Raman and INS results, we propose an assignment for the internal torsion and for the librational motions in the intercalated organometallic cations. An estimate of the potential barrier height against the torsion and the R′_z whole-body rotation is derived; these values are compared with those calculated for the corresponding iodide salts. We conclude that a significant decrease of the intermolecular forces acting on the rings is taking place within the interlamellar space.     

The fluorescence of all-trans diphenyl polyenes

The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S₁(¹A_g*) and S₂(¹B_u*) state assignment, and determines their energy difference ΔE. The S₁ fluorescence rate parameter k_F depends on ΔE, the solvent refractive index n, the S₂ (n = 1) fluorescence rate parameter k_F20 (2.23 × 10⁸ s^?1 for DPH, 2.33 × 10⁸ s^?1 for DPO), and the S₂-S₁ coupling matrix element V (745 cm^?1 for DPH, 500 cm^?1 for DPO). The S₁ fluorescence is induced by ¹B_u*-¹A_g* potential interaction (PI), via a b_u vibrational mode (≈ 900 cm^?1), and not by vibronic coupling. The main S₁ radiationless transition, rate parameter k_R, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S₁ (θ) potential surface and thus influences k_R.     

Assignment of the electronic transitions in benzene

The problem of the assignment of π-electronic transitions in benzene is discussed using all criteria presently available. It is shown that based on this information a few different assignments are impossible to exclude. The correct assignment ³B_1u < ³E_1u < ¹B_2u < ³B_2u < ¹B_1u < ³E⁺_2g < ¹E_1u < ¹E^?_2g < ³E^?_2g has been selected as result of theoretical considerations based on a new approach to the semi-empirical π-electron theory. The results confirm the adequacy of the π-electron model for energy level calculations, and emphasise the fundamental importance of multi-excited configurations.     

Densities,speeds of sound and isentropic compressibilities of binary and ternary mixtures containing benzene,cyclohexane and hexane at 298.15 K

Densities, ϱ, and speeds of sound, u, have been measured for the ternary mixture {benzene + cyclohexane + hexane} and the corresponding binary mixtures {benzene + cyclohexane}, {benzene + hexane} and {cyclohexane + hexane}, at the temperature 298.15 K. Using these results, the isentropic compressibilities, κ_s, the excess isentropic compressibilities, κ_s^E, and the speeds of sound deviations, Δu, have been calculated for both the binary mixtures and the ternary system. Excess isentropic compressibilities, κ_s^E, and the speeds of sound deviations, Δu, have been fitted to the Redlich-Kister equation in the case of binary mixtures, while the equation of Cibulka was used to fit the values relating to the ternary system. The empiric equations of Redlich-Kister, Tsao-Smith, Kohler and Colinet have been applied in order to predict the κ_s^E and Δu of ternary mixtures from the binary contributions.     

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.     

IR- and Raman-active normal vibrations of rare earth oxyfluorides,REOF; RE=Y,La, and Gd

The vibrational levels of selected rhombohedral rare earth oxyfluorides, REOF; RE = La, Gd, and Y, were deduced from the room temperature IR absorption and the Raman scattering spectra between 180 and 1000 cm⁻¹ and between 10 and 700 cm⁻¹, respectively. All four IR-active (2A_2u + 2E_u) and six Raman-active (3A_1g, + 3E_g) normal modes predicted by the group-theoretical analysis for the D_3d factor group were observed. The vibrations were assigned with the aid of their intensity and frequency in good agreement with the cubic fluorite-like structure of stoichiometric REOF.     

Speeds of sound and isentropic compressibilities of binary mixtures containing trialkylamines with alkanes and mono-alkylamines at 303.15 and 313.15 K

Isentropic compressibilities κ_S, and excess isentropic compressibilities κ_S^E have been determined from measurements of speeds of sound u and densities ρ of 14 binary mixtures of triethylamine (TEA) and tri-n-butylamine (TBA) with n-hexane, n-octane, iso-octane, n-propylamine, n-butylamine, n-hexylamine and n-octylamine. The relative magnitude and sign of κ_S^E have been interpreted in terms of molecular interactions and interstitial accommodation. The values of κ_S^E for TEA + alkane are positive while for TBA + alkane are negative. The values of κ_S^E for TEA + primary amine become progressively less positive and eventually to negative with the increase in chain length of alkylamine. In case of TBA + primary amine, the values of κ_S^E increase from n-propylamine to n-butylamine, and then decrease with chain length of primary amine. The experimental speeds of sound u have been analyzed in terms of collision factor theory, free length theory and Prigogine–Flory–Patterson statistical theory of solutions.     

The electronic absorption spectra of the alkyl-substituted derivatives of bis(benzene)chromium(0) in the vapour phase

The UV and visible absorption spectra of (arene)₂chromium(0) (arene = benzene (I), toluene (II), ethylbenzene (III), cumene (IV), tert-butylbenzene (V), mesitylene (VI) in the vapour phase have been investigated. Four band systems A,B,C and D are revealed in the spectra. The bands of the system with the shortest wavelengths, D, represent the Rydberg series. The first ionisation potentials IP_a1g, 5.18 and 5.01 eV respectively. The Rydberg bands correspond to the allowed electrodipole transitions from the highest occupied molecular orbital (MO) a_1g to the vacant MO of either the a_2u or e_1u type.System C corresponds to the intense band of the solution spectra. The electronic transition e_2g → e_2g obviously makes a great contribution to this system. System B is assigned to the transition from a_1g to vacant a_2u or e_1u MO, which can be Rydberg orbitals. System A can be assigned to the a_1g → e_2u transition or to the Rydberg transition, which is forbidden in the D_6h point group but becomes allowed upon reduction of symmetry.