Thermodynamic functions of lactones in the gaseous state

© 2016, Springer Science+Business Media New York.The temperature dependences of the vapor pressures of oxacyclobutan-2-one and oxacyclopentan-2-one were measured by the transpiration method. The entropies of gaseous oxacycloalkan-2-ones (lactones) were determined based on the experimental values of entropy in the condensed state, vapor pressure, and enthalpy of vaporization. Thermodynamic functions of lactones with a ring size of n = 4—8 (number of atoms in the ring) were determined by quantum chemistry and statistical physics methods in the ideal gas approximation taking into account the molar fractions of all conformers and optical isomers in the temperature range from 298.15 to 1500 K. The enthalpies of ring strain were calculated based on the enthalpies of formation

Scanning tunneling microscopy and spectroscopy at low temperatures of the (110) surface of Te doped GaAs single crystals

We have performed voltage dependent imaging and spatially resolved spectroscopy on the (110) surface of Te doped GaAs single crystals with a low temperature scanning tunneling microscope (STM). A large fraction of the observed defects are identified as Te dopant atoms which can be observed down to the fifth subsurface layer. For negative sample voltages, the dopant atoms are surrounded by Friedel charge density oscillations. Spatially resolved spectroscopy above the dopant atoms and above defect free areas of the GaAs (110) surface reveals the presence of conductance peaks inside the semiconductor band gap. The appearance of the peaks can be linked to charges residing on states which are localized within the tunnel junction area. We show that these localized states can be present on the doped GaAs surface as well as at the STM tip apex.Comment: 8 pages, 8 figures, accepted for publication in PR

Orbital features of distant trans-Neptunian objects induced by giant gaseous clumps

Context. The discovery of distant trans-Neptunian objects has led to heated discussions about the structure of the outer Solar System. Aims. We study the dynamical evolution of small bodies from the Hill regions of migrating giant gaseous clumps that form in the outer solar nebula via gravitational fragmentation. We attempt to determine whether the observed features of the orbital distribution of distant trans-Neptunian objects could be caused by this process. Methods. We consider a simple model that includes the Sun, two point-like giant clumps with masses of ∼10 Jupiter masses, and a set of massless objects initially located in the Hill regions of these clumps. We carry out numerical simulations of the motions of small bodies under gravitational perturbations from two giant clumps that move in elliptical orbits and approach each other. The orbital distribution of these small bodies is compared with the observed distribution of distant trans-Neptunian objects. Results. In addition to the known grouping in longitudes of perihelion, we note new features for observed distant trans-Neptunian objects. The observed orbital distribution points to the existence of two groups of distant trans-Neptunian objects with different dynamical characteristics. We show that the main features of the orbital distribution of distant trans-Neptunian objects can be explained by their origin in the Hill regions of migrating giant gaseous clumps. Small bodies are ejected from the Hill regions when the giant clumps move in high-eccentricity orbits and have a close encounter with each other. Conclusions. The resulting orbital distribution of small bodies in our model and the observed distribution of distant trans-Neptunian objects have similar features

Thermodynamic functions of lactones in the gaseous state

© 2016, Springer Science+Business Media New York.The temperature dependences of the vapor pressures of oxacyclobutan-2-one and oxacyclopentan-2-one were measured by the transpiration method. The entropies of gaseous oxacycloalkan-2-ones (lactones) were determined based on the experimental values of entropy in the condensed state, vapor pressure, and enthalpy of vaporization. Thermodynamic functions of lactones with a ring size of n = 4—8 (number of atoms in the ring) were determined by quantum chemistry and statistical physics methods in the ideal gas approximation taking into account the molar fractions of all conformers and optical isomers in the temperature range from 298.15 to 1500 K. The enthalpies of ring strain were calculated based on the enthalpies of formation

A study of the electronic structure and properties of the propargyl radical

© 2016, Pleiades Publishing, Ltd.By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH2CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH2CCH are studied at the qualitative level. Characteristics of the electronic structure of CH2CCH and its parent molecules CH3–C≡CH and CH2=C=CH2 are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH2CCH is considered and its conjugation energy is calculated

Benchmarking thermochemical experiments and calculations of nitrogen-containing substituted adamantanes

© 2016, Akadémiai Kiadó, Budapest, Hungary.Standard molar enthalpy of formation of 2-cyano-adamantane was obtained by using high-precision combustion calorimetry. The standard molar enthalpies of sublimation of 2-cyano-adamantane and 2,2-dinitro-adamantane at 298.15 K were derived from the vapor pressure temperature dependences measured by transpiration. The molar enthalpies of fusion of these compounds were measured with the help of differential scanning calorimetry. Thermochemical data on functional substituted adamantanes containing nitrogen in the substituents were collected and evaluated. The gas-phase enthalpies of formation were calculated with the high-level quantum-chemical method G4 and compared with the experimental results. The consistent data set of the benchmark quality was suggested for practical thermochemical calculations. Geminal destabilizing effects for the interactions of nitro- and cyano-substituents placed in the second position on the adamantane cage were derived. Structure–property correlations for substituted adamantanes and aliphatic substituted alkanes were found and suggested for the assessment of the gas-phase enthalpies of formation of adamantane derivatives

A study of the electronic structure and properties of the propargyl radical

© 2016, Pleiades Publishing, Ltd.By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH2CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH2CCH are studied at the qualitative level. Characteristics of the electronic structure of CH2CCH and its parent molecules CH3–C≡CH and CH2=C=CH2 are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH2CCH is considered and its conjugation energy is calculated