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Vaporization/sublimation enthalpies for twenty-one disubstituted benzenes were calculated from dissolution enthalpies and solvation enthalpies in four solvents of different polarity: carbon tetrachloride, benzene, N,N-dimethylformamide, and acetonitrile. The values of solvation enthalpy were calculated using group-additivity scheme for each solvent. Dissolution enthalpies of some substances were taken from literature and fifty-six original values were measured in the present work. The calculated values of vaporization/sublimation enthalpy were compared with the literature data. It was concluded that calculated vaporization/sublimation enthalpies do not depend on the choice of solvents excluding those that interact with the solute specifically.

In this work a simple method for calculation of solvation enthalpies of polyaromatic hydrocarbons (PAHs) in various solvents at 298.15 K was proposed. According to this method the enthalpy of solvation of any polyaromatic hydrocarbon in a particular solvent can be calculated on the basis of the general formula of the compound, the solvation enthalpy of benzene in the same solvent and parameter related to the contribution of hydrogen atom into solvation enthalpy. The validity of the proposed method was confirmed by the comparison of calculated and experimentally measured values of solvation enthalpies of PAHs in benzene, tetrahydrofuran and acetonitrile. This method was used for determination of the sublimation enthalpy of PAHs at 298.15 K based on the general relationship between the enthalpy of sublimation/vaporization of the compound of interest and its enthalpies of solution and solvation in the same solvent at 298.15 K. Enthalpies of solution at infinite dilution of several PAHs were measured in acetonitrile, benzene and tetrahydrofuran at 298.15 K. It was shown that solution enthalpies of PAHs in benzene at 298.15 K are approximately equal to their fusion enthalpies at the melting temperature. Solvation enthalpies of 15 PAHs at 298.15 K calculated according to the proposed method together with corresponding fusion enthalpy values (at the melting temperature) were used to calculate the sublimation enthalpy values at 298.15 K. Comparison of the obtained results with recommended values of sublimation enthalpy shows that fusion enthalpies at the melting temperature can be used instead of the solution enthalpies in benzene at 298.15 K for calculation of the sublimation enthalpy at 298.15 K.

In this work a new method for determination of vaporization/sublimation enthalpies of aromatic compounds directly at T = 298.15 K was developed. This method is based on the general relationship between vaporization/sublimation enthalpy and enthalpies of solution and solvation of the studied compound in any solvent. According to this method the procedure for determination of vaporization (liquids) or sublimation (solids) enthalpy includes measurement of the solution enthalpy of the compound in a selected solvent and calculation of the solvation enthalpy for this system. A group-additivity scheme for calculation of solvation enthalpies is proposed. The solvation enthalpy of compound is estimated from the solvation enthalpy of parent aromatic or heteroaromatic compound and contributions of the substituent groups. Limiting solution enthalpies of 34 aromatic compounds (substituted benzenes, naphthalenes, biphenyls, pyrene, anthracene and pyridines) in carbon tetrachloride, benzene, acetonitrile and N,N-dimethylformamide were measured in the present work at 298.15 K. Vaporization/sublimation enthalpies of 78 aromatic and heteroaromatic compounds were determined directly at 298.15 K using experimentally measured solution enthalpies and predicted values of solvation enthalpies. The results are in good agreement with available literature data.

The enthalpies of solution, solvation and vaporization/sublimation are interrelated values combined in the simplest thermodynamic circle. Hence, experimental determination of vaporization/sublimation enthalpy can be substituted by experimentally simpler determination of solution enthalpy when solvation enthalpy is known. Previously it was found that solvation enthalpies of a wide range of unbranched aliphatic and aromatic solutes in saturated hydrocarbons are in good linear correlation with their molar refraction values. This allows to estimate the vaporization/sublimation enthalpy of any unbranched organic compound from its solution enthalpy in saturated hydrocarbon and molar refraction. In the present work this approach was modified for determination of vaporization/sublimation enthalpy of branched-chain alkyl aromatic and aliphatic compounds. Group contributions to the enthalpy of solvation due to the branching of carbon chain were evaluated. Enthalpies of solution at infinite dilution of 18 branched-chain aliphatic and alkyl aromatic compounds were measured at T = 298.15 K. Vaporization/sublimation enthalpies for 35 branched aliphatic and alkyl aromatic compounds were determined by using modified solution calorimetry approach. These values are in good agreement with available literature data on vaporization/sublimation enthalpies obtained by conventional methods.

In this work a new solution-based calorimetry approach for determination of the sublimation and vaporization enthalpies of low volatile compounds was proposed. The approach is based on the measurement of solution enthalpy of a molecule of interest in benzene and as well as the measurement of molar refraction index for this molecule. Enthalpies of solution at infinite dilution in benzene for a set of 18 aromatic and polyaromatic hydrocarbons were measured at 298.15 K. Experimental data on vaporization/sublimation enthalpies for this set were collected from the literature. For validation of the literature data additional sublimation experiments were performed for phenanthrene, 1-phenylnaphthalene, 1,2-diphenylbenzene, 1,2,3,4-tetraphenylnaphthalene, hexaphenylbenzene, and rubrene using transpiration, quartz crystal microbalance, and thermogravimetry. Vaporization/sublimation enthalpies derived from the solution calorimetry approach were in good agreement (within experimental uncertainties) with those measured by conventional methods. The solution-based calorimetry approach gives a reliable and quick appraisal of vaporization/sublimation enthalpies. This approach constitutes a complementary additional thermochemical option for vaporization/sublimation enthalpies data evaluation as well as for rapid data gathering for low volatile and/or thermally unstable organic compounds.

The work is devoted to the investigation of thermodynamics of specific interaction of the tertiary aliphatic and aromatic amines with associated solvents as which aliphatic alcohols were taken. Solution enthalpies of aliphatic alcohols in amines (tri-n-propylamine, 2-methylpyridine, 3-methylpyridine, N-methylimidazole) as well as amines in alcohols were measured at infinite dilution. The enthalpies of specific interaction (H-bonding) in systems studied were determined based on experimental data. The enthalpies of specific interaction of amines in aliphatic alcohols significantly lower than the enthalpies of hydrogen bonding in complexes amine–alcohol of 1:1 composition determined in base media due to the reorganization of aliphatic alcohols as solvents. The determination of solvent reorganization contribution makes possible to define the hydrogen bonding enthalpies of amines with clusters of alcohols. Obtained enthalpies of hydrogen bonding in multi-particle complexes are sensitive to the influence of cooperative effect. It was shown, that hydrogen bond cooperativity factors in multi-particle complexes of alcohols with amines are approximately equal for all alcohols when pyridines and N-methylimidazole as solutes are used. At the same time, H-bonding cooperativity factors in complexes of trialkylamines with associative species of alcohols decrease with increasing of alkyl radical length in alcohol and amine molecules. This work shows that the thermodynamic functions of specific interaction of solutes with associated solvents cannot be described using the H-bond parameters for the complexes of 1:1 composition.

Mechanical properties of miscible blends of high molecular weight poly(N-vinyl pyrrolidone) (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) of molecular weight 400 g/mol have been examined as a function of PVP–PEG composition and degree of hydration. The small-strain behavior in the linear elastic region has been evaluated with the dynamic mechanical analysis and compared with the viscoelastic behavior of PVP–PEG blends under large strains in the course of uniaxial drawing to fracture and under cyclic extension. A strong decoupling between the small-strain and the large strain properties of the blends has been observed, indicative of a pronounced deviation from rubber elasticity in the behavior of the blends. This deviation, also seen on tensile tests under fast drawing, is attributed to the peculiar phase behavior of the blends and the molecular mechanism of PVP–PEG interaction. Nevertheless, for the PVP blend with 36% PEG, under comparatively low extension rates, the reversible contribution to the total work of deformation up to e=300% has been found to be maximum at around 70%, while the blends containing 31 and 41% PEG behave rather as an elastic–plastic solid and a viscoelastic liquid, respectively.

The SIGMA telescope realizes images of the sky in the hard X-ray domain (40 keV–1.3 MeV) through a coded mask system. The extragalactic study was one of the main objectives and has brought new results in our knowledge of the Active Galactic Nuclei behavior at high energy. In fact, the variability is the most important factor as all these objects have been showed to display strong evolution in intensity or/and spectral shape. Moreover, the discovery of a new hard X-ray source close to 3C273 and probably strongly absorbed below 40–50 keV could have many consequences in the extragalactic field.

The field containing the newly discovered soft γ-ray source GRS 1758-258, located 40 arcmin. away from GX 5-1, was observed by the SIGMA telescope on board the soviet spacecraft GRANAT in the course of the five extensive galactic-center surveys performed in 1990, 1991 and 1992. In both 1990 surveys, as well as in the February–April 1991 survey, the source exhibits a Cygnus X-1 like spectrum with nearly constant flux, while in the most recent measurements on September–October 1991 and spring 1992, a long term low-state has been discovered with an upper limit on the source flux five time lower than the average flux measured by SIGMA during all the observations from March 1990 until April 1991.

After more than two years of operation, the imaging γ-ray SIGMA telescope has accumulated several days of observation toward well known X-ray binaries. Four bright sources falling in this category have been detected so far: The pulsar GX 1+4 near the center of our galaxy, the stellar wind accreting system 4U 1700-377, and the black hole candidates Cygnus X-1 and GX 339-4. Moreover, SIGMA have observed three transients sources, which turned out to be also hard X-ray sources : The burster KS 1731-260, Tra X-1, and the Musca Nova. The properties of these systems in the SIGMA domain will be reviewed and a spectral distinction between black holes and neutron stars will be sketched.

The X-ray system GX339-4 has been observed on several occasions between March 1990 and September 1991 with the SIGMA hard X-Ray/soft gamma-ray imaging telescope (35 keV–1.3 MeV) on board the GRANAT observatory /1/. This object was detected in hard and soft states, as well as during a transition between these two states. We analyse the spectral and temporal behaviour of this black hole candidate.

Unlike black hole candidate systems, accreting neutron stars seem to encounter appreciable difficulties in emitting strong hard X-ray fluxes. However, in the catalogue of the hard X-ray sources detected by SIGMA, three sources are associated with type I X-ray bursters. In this paper, we review the present status of the SIGMA observations of these three X-ray burst sources, namely X 1724-308 in the globular cluster Terzan II, KS 1731-260, and GX 354+0.

The launch in December 1989, of SIGMA, one of the main devices aboard the GRANAT spacecraft, has provided high-energy astronomers for the first time with a telescope whose imaging properties in the soft γ-ray regime match those of instruments operating in the hard X-ray band. Having examined ∼ 300 celestial fields during more than two years of successful in-orbit operations, this coded-aperture telescope, sensitive to radiation in the energy range 35 keV to 1.3 MeV, has succeeded both in disentangling severe source confusion problems and in providing firm identifications and reliable spectra of sources at soft γ-ray wavelengths. A selection of the salient scientific results obtained so far is presented, with intent to emphasize the unique contribution of a coded-mask telescope able to perform accurate images of the sky in the soft γ-ray domain.

We report the first detection of two soft gamma ray transients GX 354-0 and Nova Persei (GRO J0422+32) by the coded-mask telescope SIGMA. Only preliminary results are presented with regard to Nova Persei while special emphasis is given to the data on GX 354-0 which has been monitored during the 1992 February–April survey of the Galactic Center. GX 354-0 underwent two flares of about two week duration and its average spectrum is well described by a thermal Bremsstrahlung model or a broken power law whereas the Nova Persei spectrum seems to be similar to the one observed for GRS 1124-684 in Musca.

Preliminary results from the SIGMA telescope observations of the Galactic Centre in the energy range of 35 keV - 1.3 MeV are presented and discussed. The telescope makes use of the coded aperture imaging technique. Our images from 35 to 300 keV reveal a strong source identified without any doubt with 1E 1740.7–2942, i. e. more than 45 arcmin away from the Galactic Nucleus. If this source is at the distance of the Galactic Centre, it is one of the most luminous objects in the galaxy at these energies.

The anticoincidence shield of the SIGMA telescope is being used as a Gamma-Ray Burst detector. Six months after the launch of the GRANAT spacecraft, a dozen bursts have been detected whose main characteristics are presented here; in particular, the first observations reveal a unusually high rate of short, hard bursts.

The region of the sky containing the Crab Nebula and its pulsar was observed by SIGMA several times during February and March, 1990. Data in the energy range 30–1300 keV were recorded in different functioning modes. One observation of ∼ 2 hours in timing mode allowed us to study the pulsed emission from PSR 0531+21. The pulsed signal has been detected up to ∼ 500 keV. We report here the results of the timing and spectral analysis of the data recorded in this observation.