Volume 219, Issue 2 - 2

IR spectroscopy, mass spectrometry, and quantum chemical calculations are employed to characterize the intermolecular interaction of a variety of aromatic cations (A + ) with several types of solvents. For this purpose, isolated ionic complexes of the type A + –L n , in which A + is microsolvated by a controlled number ( n ) of ligands (L), are prepared in a supersonic plasma expansion, and their spectra are obtained by IR photodissociation (IRPD) spectroscopy in a tandem mass spectrometer. Two prototypes of aromatic ion–solvent recognition are considered: (i) microsolvation of acidic aromatic cations in a nonpolar hydrophobic solvent and (ii) microsolvation of bare aromatic hydrocarbon cations in a polar hydrophilic solvent. The analysis of the IRPD spectra of A + –L dimers provides detailed information about the intermolecular interaction between the aromatic ion and the neutral solvent, such as ion–ligand binding energies, the competition between different intermolecular binding motifs (H-bonds, π-bonds, charge–dipole bonds), and its dependence on chemical properties of both the A + cation and the solvent type L. IRPD spectra of larger A + –L n clusters yield detailed insight into the cluster growth process, including the formation of structural isomers, the competition between ion–solvent and solvent–solvent interactions, and the degree of (non)cooperativity of the intermolecular interactions as a function of solvent type and degree of solvation. The systematic A + –L n cluster studies are shown to reveal valuable new information about fundamental chemical properties of the bare A + cation, such as proton affinity, acidity, and reactivity. Because of the additional attraction arising from the excess charge, the interaction in the A + –L n cation clusters differs largely from that in the corresponding neutral A–L n clusters with respect to both the interaction strength and the most stable structure, implying in most cases an ionization-induced switch in the preferred aromatic molecule–solvent recognition motif. This process causes severe limitations for the spectroscopic characterization of ion–ligand complexes using popular photoionization techniques, due to the restrictions imposed by the Franck–Condon principle. The present study circumvents these limitations by employing an electron impact cluster ion source for A + –L n generation, which generates predominantly the most stable isomer of a given cluster ion independent of its geometry.

This paper is concerned with the dielectric relaxation times (τ) and the dipole moments (μ) of the binary mixtures of different molar concentrations of acetonitrile (CH 3 CN) in the binary mixtures of N-Methylacetamide (NMA) and acetonitrile (CH 3 CN) in benzene solutions. The physical parameters τ and μ have been calculated by using standard standing wave microwave techniques and Gopala Krishna’s single frequency (9.90 GHz) concentration variational method at different temperatures (25 °C, 30 °C, 35 °C, 40 °C). The dielectric relaxation process have been found to be an activated process. The energy parameters (Δ H , Δ F , Δ S ) for the dielectric relaxation process of binary mixtures containing 30% mole-fraction of CH 3 CN have been calculated at the respective given temperatures and a comparison has been made with the corresponding energy parameters (Δ H η , Δ F η , Δ S η ) for the viscous flow. On the basis of the observations, it is found that the dielectric relaxation process can be treated as the rate process like the viscous flow process. Solute–solute and solute–solvent molecular associations have been predicted.

The binary anisotropic and isotropic collision-induced light scattering spectra by gaseous room temperature neon, over an extended frequency domain have been used for deriving the empirical multi-parameter Morse–Morse–Morse–Spline van der Waals interatomic potential. These new data of scattering are accurate enough to permit for the first time a reliable determination of the isotropic potential as a function of the interatomic separation. The potential parameters describing the location and depth of the attractive well are given by ε = 41.07 K and r m = 3.087 Å. Comparison with other potentials based on bulk properties and ab initio calculations are presented; the temperature dependence of pressure second virial coefficient, self diffusion, thermal conductivity and viscosity are also discussed for the proposed potentials. In addition, our empirical potential was used to solve the nuclear Schrödinger equation for comparison with and predication of spectroscopic properties of the dimer. The results show that it is the most accurate potential reported to date for this system.

The reactions      NH(a) + HN 3 (X̃) → prod.       (1) and                     NH(a) + NH 3 (X̃) → prod.       (2) were studied in a quasi-static reaction cell in the temperature range 293 ≤ T /K ≤ 501 at a pressure of 10 mbar and 20 mbar, respectively, with He as the main carrier gas. The electronically excited reactant NH(a) was generated by laser-flash photolysis of HN 3 , at λ = 308 nm and detected by laser-induced fluorescence (LIF). Also the ground state species NH(X) was detected by LIF. From the measured concentration-time profiles of NH(a) under pseudo-first order conditions, the rate coefficients k 1 ( T ) and k 2 ( T ) were obtained. For the rate coefficient k 1 a positive temperature dependence was observed: k 1 ( T ) = (8.1 ± 0.5) × 10 13 exp[(−0.76 ± 0.05)/ RT ] cm 3 /mol s with a small activation energy of E A = 0.76 kJ/mol. For reaction (2) the rate coefficient k 2 ( T ) = (8.6 ± 0.6) × 10 13 ( T /298) −(0.6 ± 0.1) cm 3 /mol s with a negative temperature dependence was measured indicating that the intermediate N 2 H 4 , which decomposes to 2 NH 2 , is formed without a barrier. The rate of the quenching channel NH(a) + NH 3 → NH(X) + NH 3        (2q) has the same temperature dependence as the rate of the overall reaction (2). The contribution k 2 q / k 2 = 0.008 over the temperature range 293 ≤ T /K ≤ 501.

DFT ab initio calculations of 22 free radical derived nucleosides analogs were performed in gas phase and water solution. Most of studied compounds exist mainly in expected amino- and keto- forms. However, there were found few important exceptions: enol-amino tautomer of 2-OH-adenosine is dominant in apolar environment, while in polar solution keto-amino isomer become more probable; 8-oxo-guanosine is to be represented as a mixture of two tautomers: 6,8-diketo and 6-enol-8-keto with disfavoring of the latter in polar conditions, 5-OH-cytidine adopts imino-keto form in non-polar surroundings but water stabilizes amino-keto isomer reverting order of these tautomers, cytidine glycol in apolar and polar conditions is represented mainly by keto-imino form, but more polar environment increase percentage of amino-keto tautomer not reverting their order, 6-hydroxy-5,6-dihydroxycytidine in both polar and non-polar conditions adopts keto-imino form, which dominates over keto-amino one, 5-hydroxy-5,6-dihydro-cytosine in non-polar conditions exists as keto-imino tautomer while polar conditions favors keto-amino form.

Thermochemical cycles have been investigated for quite some time as a means to convert heat into storable chemical energy. A particularly attractive reaction is the solar-thermal decomposition of zinc oxide into zinc and oxygen, but the efficiency of this process is impaired by the fast recombination of zinc and oxygen upon cooling of the gas phase. The combination with a second, nickel/nickel oxide redox cycle is presented as a possibility to avoid the simultaneous presence of metal and oxygen in the gas phase.

The density of the melts in the system LiF–NaF–K 2 NbF 7 has been measured using an Archimedean method. Based on the measured density values, the molar volumes, partial molar volumes and excess molar volumes of the melts were calculated. The measurement of density in the investigated system has shown that a significant ternary interaction exists in the melts, which can be ascribed to the formation of different complex anions.

General relations among the thermodynamic parameters, which characterize dissociation equilibria of an acid HA in both phases of a two-phase extraction system and ion transfers across the interface of this system, was formulated. Moreover, dissociation constant of 2-nitroso-1-naphthol in nitrobenzene saturated with water was calculated as p K d nb (HA) = −log K d nb (HA) = 16.48.