Heterogeneous reactions of SO2 with HOCl and HOBr on ice surfaces

The heterogeneous reactions of SO2 + HOX (X = Cl or Br) --> products on ice surfaces at low temperature have been investigated in a flow reactor coupled with a differentially pumped quadrupole mass spectrometer. Pseudo-first-order loss of SO2 over the ice surfaces has been measured under the conditions of concurrent HOX flow. The initial uptake coefficient of SO2 reaction with HOX has been determined as a function of HOX surface coverage, theta(HOX), on the ice. The initial uptake coefficients increase as the HOX coverage increases. The uptake coefficient can be expressed as gamma(t) = k(h)theta(HOX), where k(h) is an overall rate constant of SO2 + HOCl, which was determined to be (2.3 +/- 0.6) x 10(-19) and (1.7 +/- 0.5) x 10(-19) molecules(-1) x cm2 at 190 and 210 K, and k(h) of SO2 + HOBr is (6.1 +/- 2.0) x 10(-18) molecules(-1) x cm2 at 190 K. theta( HOX) is in the range 8.1 x 10(13)-9.1 x 10(14) molecules x cm(-2). The kinetic results of the heterogeneous reaction of SO2 + HOX on ice surface are interpreted using the Eley-Rideal mechanism. The activation energy of the heterogeneous reaction of SO2 with HOCl on ice surface was determined to be about -37 +/- 10 kJ/mol in the 190-238 K range.     

Die Systeme K2NaAlF6/Na2SO4 und K2NaAlF6/K2SO4 Phasendiagramme und Alkaliionenleitung

On the Systems K₂NaAlF₆/Na₂SO₄ and K₂NaAlF₆/K₂SO₄: Phase Diagrams and Alkali Ion Conductivity The phase diagrams of the K₂NaAlF₆/Na₂SO₄ and K₂NaAlF₆/K₂SO₄ systems have been determined by means of thermal, x-ray powder and electrochemical methods in the solidus-liquidus and the sub-solidus region, as well. At the optimum combination of parameters, the alkaliion conductivity increased by about three orders of magnitude upon doping K₂NaAlF₆ with Na₂SO₄ and/or K₂SO₄.     

Study on electrochemical performance of activated carbon in aqueous Li2SO4, Na2SO4 and K2SO4 electrolytes

The electrochemical performances of activated carbon (AC) in 0.5 mol/l Li₂SO₄, Na₂SO₄ and K₂SO₄ aqueous electrolytes were investigated. The cyclic voltammetric results at different scan rates show that the rate behaviors of AC in the three electrolytes improve in the order of Li₂SO₄ < Na₂SO₄ < K₂SO₄. This improvement can be mainly ascribed to the following two reasons: (1) the decreasing equivalent series resistance in the order of Li₂SO₄ > Na₂SO₄ > K₂SO₄, which is the main factor influencing the maximum output power, and (2) the increasing migration speed of hydrated ions in the bulk electrolyte and in the inner pores of AC electrode in the order of Li⁺ < Na⁺ < K⁺. Their cycling behaviors do not show any differences in capacitive fading. The above results provide valuable information to explore new hybrid supercapacitors.     

Theoretical investigation of the SO(2+) dication and the photo-double ionization spectrum of SO

Highly correlated ab initio methods were used in order to generate the potential energy curves of the electronic states of the SO(2+) dication and of the electronic ground state of the neutral SO molecule. These curves were used to predict the spectroscopic properties of this dication and to perform forward calculations of the double photoionization spectrum of SO. In light of spin-orbit calculations, the metastability of this doubly charged ion is discussed: for instance, the rovibrational levels of the X (1)Sigma(+) and A (3)Sigma(+) states are found to present relatively long lifetimes. In contrast, the other electronic excited states should predissociate to form S(+) and O(+) in their electronic ground states. The simulated spectrum shows structures due to transitions between the v=0 vibrational level of SO (X (3)Sigma(-)) and the vibrational levels below the barrier maximum of 11 of the calculated electronic states. The 2 (1)Sigma(+) electronic state of SO(2+) received further treatment: in addition to vibrational bands due to the below barrier energy levels of this electronic state, at least nine continuum resonances were predicted which are responsible for the special shape of the spectrum in this energy region. This work is predictive in nature and should stimulate future experimental investigations dealing with this dication.     

The system K2SO4-K2S

A new experimental technique has been developed to determine the phase equilibrium diagram for the system K₂SO₄-K₂S.The technique involves isothermal thermogravimetry of potassium sulphate during reduction to potassium sulphide at elevated temperatures in a stream of dry oxygen-free hydrogen gas. Several abrupt changes in the rate of weight loss occur in each curve and these can be related to phase changes in the phase diagram for the system.On the basis of such results the liquidus and solidus (solid solution) boundaries can be located.Simple thermal analysis is used to confirm the eutectic temperature and various liquidus temperatures.The diagram K₂SO₄-K₂S is a simple eutectic system with the eutectic at 610 and 23 mole % K₂S. The limits of solid solubility of K₂S in K₂SO₄ and K₂SO₄ in K₂S at the eutectic temperature are 11 % and 36 mole% respectively.The odd shape of the liquidus curves on each side of the eutectic suggests the possibility of phase changes in both K₂SO₄ and K₂S solid solutions. No evidence for this was obtained from thermal analysis.

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Zusammenfassung Eine neue experimentelle Technik wurde zur Bestimmung des Phasengleichgewichtsdiagramms des Systems K₂SO₄-K₂S entwickelt.Die Technik umfasst die isotherme Gravimetrie von Kaliumsulfat wÄhrend der Reduktion zu Kaliumsulfid bei erhöhten Temperaturen in strömenden trockenen und Sauerstoff-freien Wasserstoff. Verschiedene plötzliche Änderungen der Geschwindigkeit des Gewichtsverlustes treten bei jeder Kurve auf und können mit den PhasenÄnderungen im Phasendiagramm des Systems in Zusammenhang gebracht werden.Durch diese Ergebnisse können die GrenzflÄchen der flüssigen und der Festphasenlösung festgestellt werden.Die einfache Thermoanalyse wird zur BestÄtigung der eutektischen Temperatur und verschiedener Liquidus-Temperaturen herangezogen.Das Diagramm K₂SO₄-K₂S ist ein einfaches eutektisches System mit dem Eutektikum bei 610 und 23 Mol % K₂S. Die Grenzwerte einer festen Lösung von K₂S in K₂SO₄ und K₂SO₄ in K₂S betragen bei der eutektischen Temperatur 11% bzw. 36 Mol %.Die aussergewöhnliche Form der Liquidus-Kurven zu beiden Seiten des Eutektikums lÄsst auf die Möglichkeit von PhasenÄnderungen in den Festlösungen von sowohl K₂SO₄ wie auch von K₂S schliessen Hierzu ergab jedoch die Thermoanalyse keine BestÄtigung.

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Résumé Une nouvelle technique expérimentale a été développée afin de déterminer le diagramme d'équilibre des phases dans le système K₂SO₄-K₂S.La technique fait appel à la thermogravimétrie isotherme du sulfate de potassium lors de sa réduction en sulfure de potassium à températures élevées dans un courant de gaz hydrogène sec exempt d'oxygène. Plusieurs changements abrupts de vitesse de perte de poids ont lieu sur chaque courbe et ces changements peuvent Être rapportés aux changements de phases dans le diagramme de phases du système.A partir de tels résultats on peut déterminer les limites du liquidus et du solidus (solution solide).L'analyse thermique simple a été utilisée pour confirmer la température eutectique etdiverses températures du liquidus.Le diagramme K₂SO₄-K₂S forme un système eutectique simple à 610 et 23 p.c. molaires de K₂S. Les limites de la solubilité en phase solide de K₂S dans K₂SO₄ et de K₂SO₄ dans K₂S sont, à la température eutectique, respectivement de 11 et 36 mol %.La forme particulière des courbes du liquidus de chaque cÔté de l'eutectique fait penser à la possibilité de changements de phases dans les solutions solides tant de K₂SO₄ que de K₂S, mais l'analyse thermique n'en a pas donné de preuve.

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K₂SO₄-K₂S . , . , . ( ). . K₂SO₄-K₂S 610 23% K₂S. K₂S K₂SO₄ K₂SO₄ K₂S , , 11 36 . K₂SO₄ K₂S . , .

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The authors would like to thank the National Research Council of Canada for their financial support.     

Spectroscopic probes of the quasi-liquid layer on ice

Raman spectra of the water OH-stretch region were acquired at air-ice and air-water interfaces at a glancing angle, which allowed observation of surface characteristics. The shapes of the OH-stretch bands indicate that the environment at the air-ice interface is different from that at the air-water interface and from that seen in bulk water. Water spectra measured at the surface of dodecane under low relative humidity indicate that this method is sensitive to fewer than 50 monolayers of water. Changes in the local environment of the surfacial water molecules may be induced by the presence of different solute species, giving rise to changes in the shape of the band. Dissolved sodium chloride disrupts hydrogen bonding in liquid water and has the same effect at the air-ice interface. However, when either HCl or HNO(3) is adsorbed from the gas phase onto an ice surface, the opposite effect is seen: Their presence appears to increase the extent of hydrogen bonding at the ice surface. At the same time, shifts in the laser-induced fluorescence spectra of acridine, a fluorescent pH-probe present at the air-ice interface, indicate that dissociation of acids occurs there. These observations suggest that the formation of hydronium ions at the air-ice interface enhances the hydrogen bonding of surfacial water molecules.     

Spectroscopic and computational studies of the intramolecular hydrogen bonding of 2-indanol

2-Indanol in its most stable form is stabilized by internal hydrogen bonding, which exists between the hydroxyl hydrogen atom and the pi-cloud of the benzene ring. A comprehensive ab initio calculation using the MP2/cc-pVTZ level of theory showed that 2-indanol can exist in four possible conformations, which can interchange through the ring-puckering vibration and the internal rotation of the OH group on the five-membered ring. A potential energy surface in terms of these two vibrational coordinates was calculated. Density functional theory calculations were used to predict the vibrational frequencies and to help in normal mode assignments. Fluorescence excitation spectra of 2-indanol confirm the presence of the four conformers in the electronic ground and excited states. The spectral intensities indicate that, at 90 degrees C, 82% of the molecules exist in its most stable form with the intramolecular hydrogen bonding. The other isomers are present at approximately 11, 5, and 3%. The MP2/6-311++G(d,p) calculation predicts a distribution of 70, 13, 9, and 8% at 90 degrees C, the experimental sample temperature.     

Spectroscopic and spin-orbit calculations on the SO+ radical cation

Highly correlated ab initio methods were used in order to generate the potential-energy curves of the SO+ electronic states correlating to S+(4Su)+O(3Pg) and S+(2Du)+O(3Pg). These curves were used for deducing accurate spectroscopic properties for these electronic states. Our calculations predict the existence of a 2Phi state lying close in energy to the well-characterized b 4Sigma- state and several weakly bound quartet and doublet states located in the 6-9 eV internal energy range not identified yet. The spin-orbit integrals between these electronic states were evaluated using these highly correlated wave functions, allowing the discussion of the metastability and the predissociation processes forming S+ +O in their electronic ground states. Multistep spin-orbit-induced predissociation pathways are suggested. More specifically, the experimentally determined dissociative potential-energy curve [H. Bissantz et al., Z. Phys. D 22, 727 (1992)] proposed to explain the rapid SO+(b 4Sigma-, v> or =13)-->S+(4Su)+O(3Pg) reaction is found to coincide with the 2 4Pi potential-energy curve for short internuclear distances and with the repulsive 1 6Pi state for longer internuclear separations.     

Adsorption, ionization, and migration of hydrogen chloride on ice films at temperatures between 100 and 140 K

Adsorption of hydrogen chloride (HCl) on water ice films is studied in the temperature range of 100-140 K by using Cs+ reactive ion scattering (Cs+ RIS), low energy sputtering (LES), and temperature-programmed-desorption mass spectrometry (TPDMS). At 100 K, HCl on ice partially dissociates to hydronium and chloride ions and the undissociated HCl exists in two distinct molecular states (alpha- and beta-states). Upon heating of the ice films, HCl molecules in the alpha-state desorb at 135-150 K, whereas those in the beta-state first become ionized and then desorb via recombinative reaction of ions at 170 K. An adsorption kinetics study reveals that HCl adsorption into the ionized state is slightly favored over adsorption into the molecular states at 100 K, leading to earlier saturation of the ionized state. Between the two molecular states, the beta-state is formed first, and the alpha-state appears only at high HCl coverage. At 140 K, ionic dissociation of HCl is completed. The resulting hydronium ion can migrate into the underlying sublayer to a depth <4 bilayers, suggesting that the migration is assisted by self-diffusion of water molecules near the surface. When HCl is covered by a water overlayer at 100 K, its ionization efficiency is enhanced, but a substantial portion of HCl remains undissociated as molecules or contact ion pairs. The observation suggests that three-dimensional surrounding by water molecules does not guarantee ionic dissociation of HCl. Complete ionization of HCl requires additional thermal energy to separate the hydronium and chloride ions.     

A computational study of the oxidation of SO2 to SO3 by gas-phase organic oxidants

We have studied the oxidation of SO(2) to SO(3) by four peroxyradicals and two carbonyl oxides (Criegee intermediates) using both density functional theory, B3LYP, and explicitly correlated coupled cluster theory, CCSD(T)-F12. All the studied peroxyradicals react very slowly with SO(2) due to energy barriers (activation energies) of around 10 kcal/mol or more. We find that water molecules are not able to catalyze these reactions. The reaction of stabilized Criegee intermediates with SO(2) is predicted to be fast, as the transition states for these oxidation reactions are below the free reactants in energy. The atmospheric relevance of these reactions depends on the lifetimes of the Criegee intermediates, which, at present, is highly uncertain.     

Spectroscopic evidence for the formation of goldfingers

Gold(I) has long been used in the treatment of rheumatoid arthritis, but the therapeutically relevant biological targets of gold(I) are not well understood. Here, we report the results of a spectroscopic investigation into the formation of goldfingers. By exploiting a thiolate to gold charge-transfer band in the UV, we observed that gold(I) interacts with zinc finger peptides with a stoichiometry of one gold ion for each two cysteine residues, forming 1:1, 1.5:1, and 2:1 adducts with zinc finger peptides containing CCHH, CCHC, and CCCC donor sets, respectively. In addition, circular dichroism experiments provided evidence that goldfingers are more ordered than the corresponding metal-free peptides but do not exhibit the canonical zinc finger structure.     

Effect of ionization on infrared and electronic absorption spectra of methyl and ethyl formate in the gas phase and in astrophysical H2O ice: a computational study

This work reports infrared and electronic absorption spectra of trans and gauche conformers of neutral ethyl formate, trans and cis conformers of neutral methyl formate, their ions in the gas phase, and neutral ethyl and methyl formate in astrophysical H(2)O ice. The second-order M?ller-Plesset perturbation (MP2) method with TZVP basis set has been used to obtain ground-state geometries. An influence of ice on vibrational frequencies of neutral ethyl and methyl formate was obtained using integral equation formalism polarizable continnum model (IEFPCM). Significant shift in vibrational frequencies for neutral methyl and ethyl formate when studied in H(2)O ice and upon ionization is observed. Rotational and distortion constants for neutral ethyl and methyl formate from this work are in excellent agreement with the available experimental values. Electronic absorption spectra of conformers of ethyl and methyl formate and their ions are obtained using time-dependent density functional method (TDDFT). The nature of electronic transitions is also identified. We suggested lines especially good to detect these molecules in interstellar medium. Using these lines, we can identify the conformers of ethyl and methyl formate in gas phase and H(2)O ice in interstellar medium. This comparative study should provide useful guidelines to detect conformers of ethyl and methyl formate and their ions in gas phase and neutral molecules in H(2)O ice in different astronomical environment.     

Gas phase dissociation of H2SO4: A computational study

The decomposition of gaseous sulfuric acid has been investigated computationally. In particular the role of the hydrated gaseous coordination adducts of SO₃(g) and H₂SO₄(g) in the (dissociation + decomposition) process has been evaluated. A first principles study of the gaseous coordination complexes SO₃(H₂O)_n (n = 1 to 3) and H₂SO₄(H₂O)_m (m = 1 to 2) has been carried out deriving equilibrium ground state structures, vibrational frequencies and energetic stabilities by the Moller–Plesset perturbation approximation. These results have been used to derive the enthalpy of formation at 0 K and the Gibbs energy functions of these molecules. A new thermodynamic modeling of the decomposition of H₂SO₄(g) has been therefore performed considering the effect of temperature, pressure and initial composition of the gas (hydration conditions).     

Spectroscopic evidence for the partial dissociation of H2O on ZnO(1010)

The interaction of water with the non-polar ZnO(1010) surface has been studied by high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). Adsorption of water at room temperature leads to the partial dissociation of water molecules giving rise to a well defined (2x1) superstructure. This observation was confirmed by the HREELS data which show the water-induced O-H stretching modes at 396 and 460 meV (3193 and 3709 cm-1) as well as the peak at 456 meV (3677 cm-1) arising from the OH species. The large red shift of the loss at 396 meV indicates unusually strong hydrogen bonding interactions of water to both neighbouring adsorbate molecules and the surface O atoms which are responsible for the partial dissociation of water molecules on the perfect ZnO(1010) surface.     

Direct observation of OH radicals ejected from water ice surface in the photoirradiation of nitrate adsorbed on ice at 100 K

Production of gaseous OH radicals in the 248-350 nm photoirradiation of NO3(-) doped on amorphous ice at 100 K was monitored directly by using resonance-enhanced multiphoton ionization. The translational energy distribution of the OH product was represented by a Maxwell-Boltzmann energy distribution with the translational temperature of 3250 +/- 250 K. The rotational temperature was estimated to be 175 +/- 25 K. We have confirmed that the OH production should be attributed to the secondary photolysis of H2O2 produced on ice surface on the basis of the results of controlled photolysis experiments for H2O2 doped on ice surface.     

Li2SO4-K2SO4-MgSO4-H2O体系及次级体系298.15K时的热化学研究

用连续滴定量热法研究Li2SO4-K2SO4-MgSO4-H2O体系及次级体系Li2SO4-K2SO40H2O、Li2SO4-MgSO4-H2O和K2SO4-MgSO4-H2O 298.15K时在离子强度为15-0.1范围内的比热容和稀释热, 并结合Debye-Huckel焓极限公式研究离子强度在15-0.0001范围内的表观摩尔焓。     

Adsorption and reaction of CO2 and SO2 at a water surface

The orientation and hydrogen bonding of water molecules in the vapor/water interfacial region in the presence of SO2 and CO2 gas are examined using vibrational sum-frequency spectroscopy (VSFS) to gain insight into the adsorption and reactions of these gases in atmospheric aerosols. The results show that an SO2 surface complex forms when the water surface is exposed to an atmosphere of SO2 gas. Reaction of SO2 with interfacial water leads to other spectral changes that are examined by studying the VSF spectra and surface tension isotherms of several salts added to the aqueous phase, specifically NaHSO3, NaHCO3, Na2SO3, Na2CO3, Na2SO4, and NaHSO4. The results are compared with similar studies of CO2 adsorption and reaction at the surface. A weakly bound surface complex is not observed with CO2.     

Investigations of CsCl,K2SO4, and K2CrO4 as high temperature calibrants for differential scanning calorimetry

The selection of reference materials having calibration quality data sets is essential to meaningful measurements with DSC. In the present work the results of critical evaluations of the data sets for such materials are reported. New studies for three salt systems, CsCl, K₂SO₄, and K₂CrO₄ as calibrants for high temperature DSC, were undertaken, and are reported. The studies were extended to include Bi and KNO₃, two prospective candidate materials for measurements at lower temperatures, and these results are also reported herewith.     

Acid-Base Equilibrium in the K2SO3-Methanol System

Russian Journal of General Chemistry -