Zdeněk Slanina

Computational study of relative stabilities of C60(Ih) and C70(D5h) gas-phase clusters

Abstract Structures, energetics, vibrations, and thermodynamics of the title species were evaluated within the AM1 semiempirical method. Whereas this method also indicates that C 70 ( D 5 h ) is the more abundant component of an equilibrium gas-phase mixture than the C 60 ( I h ) cluster, the possible effect of pressure on the relative stability of C 60 vs C 70 species was pointed out. A comparison with MMP2 and MNDO results is also made.

A theoretical evaluation of water oligomer populations in the Earth's atmosphere

Atmospheric water vapour is treated as an equilibrium mixture of gas-phase water clusters, (H2O)i, using recent precise quantum-chemical data on these species. It is shown that within a typical atmospheric temperature/humidity profile, the cluster populations in the Earths atmosphere decrease with increasing height, being of the order of magnitude of 0.1 mg/m3 and 0.1 μg/m3 for the water dimer and trimer, respectively, in the atmospheric pressure region of 700–800 mb.

Thermodynamic and kinetic consequences of isomeric interplay

Abstract This paper surveys situations where observational or theoretical means have discovered the presence of several isomeric structures in an equilibrium. The effects of this isomerism on the evaluation of thermodynamic (and also partly kinetic) quantities are studied. Particular attention is given to the coexistence of two (or more) isomeric structures of comparable stability. The convolutional and deconvolutional treatments described are important for the interpretation of the overall observed terms, the prediction of properties and the behaviour of complex mixtures as well as for theory-experiment comparisons.

Contents of molecular complexes in gas phase at higher pressures: a case study of (H2O)2(g)

Abstract The contents of weak molecular complexes have been analysed in equilibrium gaseous mixtures at high pressures, particularly in the region above the critical temperature, and have been illustrated with the water dimer using the most precise quantum-chemical data on the thermodynamics of its formation. The temperature decrease in stability can be overcompensated by the pressure. The competition action of formation of higher clusters has been studied with the model of water vapour composed of oligomers up to (and including) the pentamers.

A program for determination of composition and thermodynamics of the ideal gas-phase equilibrium isomeric mixtures

Abstract A FORTRAN program is described for the evaluation of populations of isomers in their ideal gas-phase equilibrium mixture, based on molecular parameters and energetics as input information for the construction of individual partition functions, as well as for the evaluation of the recently introduced isomerism contributions to overall thermodynamics. The program is particularly useful for the evaluation, interpretation or prediction of the behaviour of complex isomeric mixtures, under a full consideration of details of vibrational motions.

On thermodynamics of Si3(g) isomers

Abstract An interplay of isomers of Si 3 (g) is studied, basing on recent ab initio data. The two low-lying states are found to be of comparable stability (same order of magnitude of their populations) at moderate and high temperatures; this finding is insensitive to further possible improvements of the system energetics (in contrast to the low-temperature region). The isomerism contribution to the thermodynamics of the system is evaluated and the non-negligible contribution of two of energetically high-lying isomers is pointed out.

Temperature interplay of isomeric structures OC·HF(g) and CO·HF(g)

Abstract The recent finding of two local energy minima at the ab initio hypersurfaces of CO-HF system has been studied in more detail in terms of the temperature-dependent weight factors of both the isomeric structures OC·HF(g) and CO·HF(g) constructed on the basis of theoretically derived molecular data. Relative stability of the two isomers has been shown to be reversed at temperatures just above 400 K. At moderate and higher temperatures this isomerism contributes substantially to overall values of thermodynamic terms of the association of CO(g) and HF(g), the contributions of the isomerism being the most distinct with the heat capacity at constant pressure. The importance of pressure for observations at higher temperatures is also shown.

Temperature enhancement of water-oligomer populations in saturated aqueous vapour

Abstract Gas-phase water is treated as an equilibrium mixture of the clusters (H2O)i(g), their stability being described by equilibrium constants of the cluster formation, derived from available theoretical information (RRHO MCY-B/EPEN model). The cluster populations under the condition of vapour saturation are evaluated and their increase with temperature is shown. Differences in results, caused by the use of either the total pressure or the total density of the saturated steam as input information for the cluster model, are discussed.

Pressure enhancement of gas-phase water oligomer populations: a RRHO MCY-B/EPEN computational study

Existing theoretical data, including the recently suggested MCY-B water pair potential and EPEN data on water oligomers in conjunction with rigid-rotor and harmonic-oscillator (RRHO) partition functions, are combined to evaluate equilibrium constants of water associate, (H2O)i, formation. The equilibrium constant set obtained is employed to study water cluster populations under various temperatures and pressures. Within the model it is shown that the pressure dependence of the mole fraction of a cluster in the equilibrium steam exhibits a maximum. The maximum with increasing temperature is shifted towards higher pressure values, however, its height is increasing, too. The importance of the finding for an assessment of optimum conditions for a cluster observation as well as reliability of the RRHO MCY-B model of steam are discussed.

An algorithm for evaluation of the exact partition function of free internal rotation, and other quantal systems having quadratically dependent energy levels

Abstract An algorithm is described for construction of the exact partition function of free internal rotation (FIR) based on direct summation approach connected with a remainder evaluation. A program for evaluation of the FIR thermodynamics employing the algorithm is presented. The results can be applied to other quantal systems with energy levels proportional to the square of quantum number, too.