The excitation spectrum of pure liquid mesitylene in the energy range 4.5–21 eV

The fluorescence of pure liquid mesitylene at -50°C is investigated as function of excitation energy in the range 4.5–21 eV when the open surface of the liquid is excited. The normalized intensity is constant for excitation in the first two electronic absorption bands and increases significantly for excitation in the third absorption band. This increase in fluorescent quantum yield is explained as a result of reduced non-radiative transitions due to a decrease in the van der Waals interactions between the molecules at the surface of the liquid, and also by a decrease in the efficiency of excimer formation there. With increasing energy of the exciting photon photoelectrons are released which produce secondary excitations and hence cause the observed increase in fluorescent yield.     

DFT calculations with the symmetrized kohn–sham formalism for the electronic structure of the high-energy states of nitrogen dioxide

Quantum-chemical calculations of the electronic structure of the high-energy states of NO₂ were performed by the density functional method with symmetrized Kohn–Sham formalism. The results from the DFT calculation of the NO₂^* NO_2^* excited states agree well with experimental data and ab initio calculations. The reactivity of the long-lived excited state NO₂^*( [(C)\tilde]²A" ) NO_2^*\left( {{{\tilde{C}}^2}A'} \right) during photochemical conversion to NO₃ was investigated.     

The electronic structure of the SbF2−5 ion and isoelectronic species

The electronic structure of the SbF²⁻₅ion and the isoelectronic species TeF⁻₅, IF₅ and XeF⁺₅ are calculated using the Discrete Variational X_α-method (DVM-X_α). The nature of chemical Bonding is analysed in terms of a Mulliken population scheme. The factors leading to geometrical distortions of the SbF²⁻₅ coordination polyhedron are discussed. The results of calculations cast doubts on the validity of the assumption that the geometry of the anion is influenced by the lone pair.     

Synchrotron radiation induced photoionization and photodissociation of carbon monoxide in the 14–35 eV region

Carbon monoxide has been excited with monochromatic synchrotron radiation in the 14–35 eV range using the Swedish synchrotron facility MAX in Lund. The decay products were studied in various detection channels such as formed CO⁺ and C⁺ ions using mass spectroscopy and visible or VUV fluorescence using photon detection. A rich line structure is observed which is attributed to CO Rydberg series converging to theX,A,B,D,C andE states in CO⁺. While a great number of these lines are already known, some of them are classified here for the first time. The combination of information from the fluorescence spectra and the mass spectra contribute important information concerning the autoionization and predissociation of these various Rydberg series.     

A theoretical study of the lowest electronic states of azobenzene: the role of torsion coordinate in the cis–trans photoisomerization

In the present paper we report the results of a multiconfigurational computational study on potential-energy curves of azobenzene along the NN twisting to clarify the role of this coordinate in the decay of the S₂(*) and S₁(n*) states. We have found that there is a singlet state, S₃ at the trans geometry, on the basis of the doubly excited configuration n²*², that has a deep minimum at about 90° of twisting, where it is the lowest excited singlet state. The existence of this state provides an explanation for the short lifetime of S₂(*) and for the wavelength-dependence of azobenzene photochemistry. We have characterized the S₁(n*) state by calculating its vibrational frequencies, which are found to correspond to the recently observed transient Raman spectrum. We have also computed the potential-energy curve for the triplet T₁(n*) at the density functional theory B3LYP level, which indicates that in this state the isomerization occurs along the twisting coordinate.Acknowledgement The financial support from MIUR (project Modellistica delle proprietà spettroscopiche di sistemi molecolari complessi funds ex 60% and project Dinamiche molecolari in sistemi di interesse chimico funds ex 40%), from the University of Bologna (Funds for Selected Research Topics) is gratefully acknowledged.Contribution to the Jacopo Tomasi Honorary Issue     

Resonance effects on the inner-valence levels of SF6 in the photon-energy range 52–72 eV

We report the photoionization partial cross section and asymmetry parameter in the 52–72 eV photon-energy range for the inner-valence orbitais (3t_1u, 2e_g, and 4a_1g) in gaseous SF₆. These results, combined with those for the (inner valence)/(outer valence) branching ratio, indicate resonant enhancement of the inner-valence levels at ≈ 59 eV photon energy which we associate with the 3t_1u → e_g shape resonance predicted by MSM Xα calculations.     

Photoionization mass spectrometry of gaseous ethene and fluoroethenes in the energy range 280–300 eV

The photoionization mass spectra of the parent cations of ethene, fluoroethene, 1,1′-difluoroethene, cis-difluoroethene, trifluoroethene and tetrafluoroethene have been measured in the energy range 280–300 eV. Below, the C1s ionization limits strong resonances are observed, which are assigned to C(1s) → π^* and C(1s) → R transitions. The term values of the core excited valence states are strongly increased compared to those of π → π^* transitions. The 1s core hole causes negligible shifts in the Rydberg states. Ab initio MRD CI calculations are used to interpret the experimental results.     

The heat capacity of the ethylene glycol-tetrahydrofuran system over the range of tetrahydrofuran concentrations 0–20 mol %

The heat capacity of the ethylene glycol (EG)-tetrahydrofuran (THF) system was measured over the range of THF concentrations 0–20 mol % and the temperature range 0–50°C using a DSC204FI differential scanning calorimeter. It was found that the heat capacity passed through a maximum at a THF concentration of 5 mol %; the maximum became more pronounced as the temperature increased. It was suggested that the maximum was caused by microphase separation at THF concentrations of 5–10 mol %. We were unable to observe phase separation with the lower critical point visually over this concentration range up to 95°C. Original Russian Text ? M.N. Rodnikova, D.B. Kayumova, L.A. Tsvetkova, I.A. Solonina, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1196–1198.     

The luminescence of NaI:Tl for excitation in the vacuum ultraviolet (12–66 eV)

The excitation spectrum (luminescence intensity vs energy of exciting photon) of NaI:Tl is studied for excitation energies in the range 12–66 eV. When the exciting radiation is of low intensity only a prompt fluorescence is observed which shows a structured excitation spectrum. This is interpreted by the assumption of secondary excitations by energetic electrons which have been raised into the conduction band. The energy of these electrons depends on the level from which they were raised. For high illumination intensities an additional, strong, slowly rising luminescence is observed, the intensity and rise time of which depends on the energy as well as on the intensity of the exciting radiation. These results are interpreted by the assumption of trapping of electrons from the conduction band. These electrons may be raised again into the conduction band by interaction with energetic conduction band electrons. The rate for the thermal release of the trapped electrons is independent of the excitation energy. A detailed model is presented which permits the calculation of the various rate parameters from the experimental results.     

Thermodynamic properties of cellulose of various structures in the temperature range 5–370 K

The energies of combustion of cellulose samples with different supramolecular structures were determined, and the enthalpies of formation of these substances were calculated. Reliable values of the heat capacity were obtained.     

The structure effect of N,N,N′,N′-alkylamide in the extraction of uranium and thorium

In this paper, nine N,N,N,N-tetraalkyldiamides have been synthesized and the extracting ability for uranium and thorium under different conditions has been studied. All results were compared with those obtained by using tributyl phosphate (TBP) under exactly the same conditions. The extracting ability of thorium and uranium for different N,N,N,N-tetraalkyldiamides is discussed.     

Access to Hexahydrocarbazoles: The Thorpe–Ingold Effects of the Ligand on Enantioselectivity

A novel cyclization reaction of methylenemalonate with indoles is reported, and it provides efficient access to a variety of hexahydrocarbazoles. The enantioselective version was realized by a finely tuned ligand/Cu^II catalyst. The optically active hexahydrocarbazoles contain three quaternary carbon centers and are obtained in up to 99 % yield with greater than 99:1 d.r. and up to greater than 99 % ee. This reaction can be carried out on gram scale and stereoselective transformation of the product led to the core structure of a series of alkaloids from Kopsia plants.     

The phase diagram of the Ga–S system in the concentration range of 48.0–60.7 mol% S

Journal of Thermal Analysis and Calorimetry - A novel flame-retarded epoxy resins system is prepared by copolymerizing diglycidyl ether of bisphenol A (EP) with tris(3-nitrophenyl) phosphine...     

Phase equilibria in polymer–solvent systems: Progress in the field of fibers

The progress in phase equilibria of polymer-solvent systems is briefly reviewed. The features of phase diagrams intended for production of fibers with high strength, deformation, and thermal properties are considered. Some attention is given to the fundamental role of S.P. Papkov in the creation and development of scientific concepts on phase equilibria in fiber-forming polymers involving solvents.     

The structure of the SF6 molecule and the SF 6 − anion excited states

The electronic and geometric structures of the ground state and a number of excited states of the SF₆ molecule and the SF ₆ ^– anion have been calculated by the discrete-variation method of the local density-functionals. The anion was found to possess a number of states stable toward the outer electron detachment, and at least one excited state stable toward dissociation. The adiabatic electron affinity (EA) was determined as 3.46 eV at the highest level of theory. This result is correlated to the high EAs of the isovalent compound SeF₆ and TeF₆; however, it does not agree with the presently accepted experimental estimate of 1.0 ± 0.2 eV for the SF₆EA value. The basic anion configuration is octahedral with a S-F bond length of 1.717 Å. The calculated limit for the highest dissociation channel of the ground state SF ₆ ^– SF ₅ ^– + F is 1.5 eV lower than the minimum of the total energy of the neutral molecule; this is in good agreement with experimental estimates.Institute for Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 641–649, March, 1992.     

Thermal diffusion in Lennard–Jones fluids in the frame of the law of the corresponding states

This work is related to the definition of a reduced thermal diffusion coefficient thanks to numerical microscale molecular dynamics simulations. This cross transport process, also called Soret effect, couples mass flux and thermal gradient and is still largely misunderstood. For this study, we have applied a boundary driven non-equilibrium molecular dynamics algorithm on Lennard–Jones spheres mixtures. Simulations have been performed at a constant reduced supercritical state, using a van der Waals’ one fluid approximation in order to fulfil the law of the corresponding states. In binary mixtures, we have studied the molecular parameters and the molar fraction influences on thermal diffusion separately and then combined. It is shown that, on pressure and on thermal conductivity, the corresponding states law is fulfilled for a wide range of molecular parameters ratios. In this frame, we have then constructed simple correlations which relate thermal diffusion factor to the mixture parameters. Combining the relations obtained, a reduced thermal diffusion factor taking into account all the various contributions has been defined. Finally, it is shown that this relation enables us to estimate thermal diffusion in various binary and ternary mixtures of Lennard–Jones spheres representing alkanes with a maximum deviation of 15%.     

Dissociative photoionization of SiH4 in the 12–19 eV region

Relative photoexcitation spectra of ionic fragments SiH⁺₃, SiH⁺₂, SiH⁺ and Si⁺ originating from photofragmentation of molecular silane (SiH₄) have been measured in the 12–19 eV region using a time-of-flight mass-analytic method combined with synchrotron radiation as a light source. No SiH⁺₄ could be detected in a measurement time of a few microseconds. The excitation spectra show a maximum photoionization efficiency around 13.3 eV for SiH⁺₂ and around 14.8 eV for SiH⁺₃. Correlations between photoionization and dissociation are discussed. The assignment of the autoionization structure between 15 and 18 eV by Börlin et al. has been positively examined and extended to include two vibrational progressions composed of the ν₁ mode with a frequency of 1690 ± 60 cm⁻¹ and the ν₂ mode with 730 ± 80 cm⁻¹.     

Thermodynamics of the solubility of sulfamethoxydiazine in organic solvents in the range 293.15–323.15 K

The solubilities of sulfamethoxydiazine in methanol, ethanol, 1-propanol, 2-propanol, acetone, and chloroform have been determined in the range 293.15–323.15 K by a static equilibrium method. The calculated results show that the correlation of the Apelblat equation for measured systems has less deviation than that of the λh equation. The positive Δ_sol H and Δ_sol S for each system revealed that sulfamethoxydiazine being dissolved in each solvent was an entropy-driven process.     

The heat capacity and thermodynamic functions of pyromorphite over the temperature range 5–320 K

The heat capacity of natural mineral, pyromorphite Pb₅(PO₄)₃Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy, and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The standard thermodynamic functions of the mineral are C _p298.15^o = 414.98 ± 0.44 J/(mol K), S _298.15^o = 585.31 ± 0.99 J/(mol K), H _298.15^o − H ₀^o = 80.90 ± 0.08 kJ/mol, and Φ_298.15^o = 313.97 ± 0.84 J/(mol K).