The spatiotemporal evolution of a chemical system close to a Hopf bifurcation in a differential flow reactor is studied. The interaction of the Hopf-differential flow induced instabilities for the cubic autocatalator model is determined through the appropriate form of the complex Ginzburg–Landau equation for the evolving amplitude. New behaviour, including spatiotemporal chaos, is observed from this equation. These predictions are shown also to be a feature of the initial-value problem for the original autocatalator equations.
{"title":"Spatiotemporal chaos in a differential flow reactor","authors":"J. Merkin, R. Satnoianu, S. Scott","doi":"10.1039/A709156G","DOIUrl":"https://doi.org/10.1039/A709156G","url":null,"abstract":"The spatiotemporal evolution of a chemical system close to a Hopf bifurcation in a differential flow reactor is studied. The interaction of the Hopf-differential flow induced instabilities for the cubic autocatalator model is determined through the appropriate form of the complex Ginzburg–Landau equation for the evolving amplitude. New behaviour, including spatiotemporal chaos, is observed from this equation. These predictions are shown also to be a feature of the initial-value problem for the original autocatalator equations.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"19 1","pages":"1211-1216"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82260748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The free radical mechanism for the addition of Cl2 to acetylene in the gas phase has been studied. The structures and energies of reactants, transition states and products were determined through abinitio calculations of the stationary points on the potential-energy surface (PES) for the interaction of these two molecules. Using BD(T)/6-311+G(2df,2p)//CASSCF(6,6)/6-31G(d,p) level of theory, the reaction rate for the initiation step (Cl2+C2H2→Cl+C2H2Cl) was estimated as 10-18 l mol-1 s-1 (at 298.15 K). This leads to the formation of a small quantity of Cl and C2H2Cl radicals, the chain propagators, and the following steps will only occur to an appreciable extent after an induction period, which generates a measurable amount of these radicals. The following steps were studied at the UCCSD(T)/6-311+G(2df,2p)//UMP2/6-31G(d,p) level of theory. The propagation reaction C2H2+Cl→C2H2Cl occurs with an activation energy of -1.22 kcal mol-1, and produces a radical C2H2Cl, where the two hydrogens are on opposite sides of the molecule (trans-isomer). This reaction has a rate constant 2.85×1010 l mol-1 s-1 at 298.15 K. The interconversion of the two isomers of the C2H2Cl radical (cis–trans) is very fast, with a rate constant 4.75×1010 s-1 and so these species can be considered to be in equilibrium. The rate constants for the reaction C2H2Cl+Cl2→C2H2Cl2+Cl, where the products trans- and cis-1,2-dichloroethylenes are formed, are 1.95×1010 and 3.63×109 l mol-1 s-1, respectively, and those for the two polymerization reactions C2H2+C2H2Cl→C2H2C2H2Cl are ca. 102 l mol-1 s-1. Hence, the latter reactions will not compete with the formation of C2H2Cl2, and the polymerization products will not be produced in meaningful amounts. Analysis of the kinetics data gives 97.3% of the trans-1,2-dichloroethylene and 2.7% of the cis-1,2-dichloroethylene products.
研究了乙炔气相中Cl2的自由基加成机理。通过对两分子相互作用势能面(PES)上的稳态点的计算，确定了反应物、过渡态和生成物的结构和能量。利用BD(T)/6-311+G(2df,2p)//CASSCF(6,6)/6- 31g (d,p)理论水平，在298.15 K下，估计起始步骤(Cl2+C2H2→Cl+C2H2Cl)的反应速率为10-18 l mol-1 s-1，这导致了少量Cl和C2H2Cl自由基的形成，并且在诱导期后，后续步骤才会发生，产生可测量数量的这些自由基。以下步骤在UCCSD(T)/6-311+G(2df,2p)//UMP2/6-31G(d,p)理论水平上进行了研究。C2H2+Cl→C2H2Cl的增殖反应活化能为-1.22 kcal mol-1，生成自由基C2H2Cl，其中两个氢位于分子的两侧(反式异构体)。该反应在298.15 K时的速率常数为2.85×1010 l mol-1 s-1。C2H2Cl自由基的两个同分异构体(顺式-反式)的相互转化非常快，速率常数为4.75×1010 s-1，因此可以认为它们处于平衡状态。C2H2Cl+Cl2→C2H2Cl2+Cl反应生成反式和顺式-1,2-二氯乙烯的速率常数分别为1.95×1010和3.63×109 l mol-1 s-1, C2H2+C2H2Cl→C2H2C2H2Cl两个聚合反应的速率常数约为102 l mol-1 s-1。因此，后一种反应不会与C2H2Cl2的形成相竞争，聚合产物也不会产生大量的产物。动力学数据分析得出97.3%的反式-1,2-二氯乙烯和2.7%的顺式-1,2-二氯乙烯产物。
{"title":"Free radical mechanism of the Cl2 addition to acetylene","authors":"S. M. Resende, J. R. Pliego, W. B. Almeida","doi":"10.1039/A803923B","DOIUrl":"https://doi.org/10.1039/A803923B","url":null,"abstract":"The free radical mechanism for the addition of Cl2 to acetylene in the gas phase has been studied. The structures and energies of reactants, transition states and products were determined through abinitio calculations of the stationary points on the potential-energy surface (PES) for the interaction of these two molecules. Using BD(T)/6-311+G(2df,2p)//CASSCF(6,6)/6-31G(d,p) level of theory, the reaction rate for the initiation step (Cl2+C2H2→Cl+C2H2Cl) was estimated as 10-18 l mol-1 s-1 (at 298.15 K). This leads to the formation of a small quantity of Cl and C2H2Cl radicals, the chain propagators, and the following steps will only occur to an appreciable extent after an induction period, which generates a measurable amount of these radicals. The following steps were studied at the UCCSD(T)/6-311+G(2df,2p)//UMP2/6-31G(d,p) level of theory. The propagation reaction C2H2+Cl→C2H2Cl occurs with an activation energy of -1.22 kcal mol-1, and produces a radical C2H2Cl, where the two hydrogens are on opposite sides of the molecule (trans-isomer). This reaction has a rate constant 2.85×1010 l mol-1 s-1 at 298.15 K. The interconversion of the two isomers of the C2H2Cl radical (cis–trans) is very fast, with a rate constant 4.75×1010 s-1 and so these species can be considered to be in equilibrium. The rate constants for the reaction C2H2Cl+Cl2→C2H2Cl2+Cl, where the products trans- and cis-1,2-dichloroethylenes are formed, are 1.95×1010 and 3.63×109 l mol-1 s-1, respectively, and those for the two polymerization reactions C2H2+C2H2Cl→C2H2C2H2Cl are ca. 102 l mol-1 s-1. Hence, the latter reactions will not compete with the formation of C2H2Cl2, and the polymerization products will not be produced in meaningful amounts. Analysis of the kinetics data gives 97.3% of the trans-1,2-dichloroethylene and 2.7% of the cis-1,2-dichloroethylene products.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"21 1","pages":"2895-2900"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80446234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The zeolite molecular sieve Na-Y was investigated for its ability to separate benzotriazole (BTZ) from tolyltriazole (TTZ). The method used was a liquid phase slurry where activated zeolite was added to a solvent mixture containing the components to be separated. The liquid samples were analysed by FTIR spectroscopy before and after the adsorption to determine the uptake of the components. The zeolite was shown to adsorb both the additives BTZ and TTZ. The solvent effects on the adsorption of BTZ were investigated showing that maximum uptake was achieved using diisopropyl ether, in preference to isobutyl acetate or 2,6 dimethylheptan-4-one. Increasing the experimental temperature indicated that the uptake of BTZ could be increased in the solvents isobutyl acetate and 2,6-dimethylheptan-4-one. It was shown that BTZ was preferentially adsorbed to TTZ, from mixtures of the two with a selectivity of the order of two.
{"title":"THE ADSORPTION PROPERTIES OF NAY ZEOLITE FOR SEPARATION OF AROMATIC TRIAZOLES","authors":"Nicola L. Singleton, K. Huddersman, M. Needham","doi":"10.1039/A806370B","DOIUrl":"https://doi.org/10.1039/A806370B","url":null,"abstract":"The zeolite molecular sieve Na-Y was investigated for its ability to separate benzotriazole (BTZ) from tolyltriazole (TTZ). The method used was a liquid phase slurry where activated zeolite was added to a solvent mixture containing the components to be separated. The liquid samples were analysed by FTIR spectroscopy before and after the adsorption to determine the uptake of the components. The zeolite was shown to adsorb both the additives BTZ and TTZ. The solvent effects on the adsorption of BTZ were investigated showing that maximum uptake was achieved using diisopropyl ether, in preference to isobutyl acetate or 2,6 dimethylheptan-4-one. Increasing the experimental temperature indicated that the uptake of BTZ could be increased in the solvents isobutyl acetate and 2,6-dimethylheptan-4-one. It was shown that BTZ was preferentially adsorbed to TTZ, from mixtures of the two with a selectivity of the order of two.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"18 1","pages":"3777-3780"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82506488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have employed scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), wide-angle X-ray scattering (WAXS), small-angle neutron scattering (SANS) and adsorption isotherms to characterise the recompressed, exfoliated graphite ‘Papyex’. The substrate is found to consist of ca. 60% void space, most of which is associated with galleries with a thickness of ca. 300 A. The substrate contains ca. 70% rhombohedral and 30% hexagonal graphite crystallites with dimensions of the order of several hundred angstroms. We confirm that Papyex has preferentially oriented graphite (0001) planes whose surfaces mainly contribute to the total available surface area. Using the theory of Debye etal., the substrate may be classed as a random two-phase structure. SANS experiments employing contrast variation show that the voids in Papyex are connected and fillable. A Guinier analysis is inappropriate to apply to the present system owing to the large scale and interconnected nature of the void space of the galleries. BET analysis shows Papyex is a non-porous or macroporous material giving a Type II isotherm with a surface area of ca. 20 g−1 and negligible micropores. This suggests that the substrate consists of voids and macroscopic cracks and fissures with dimensions of the order of ca. 500 A or more. Porod analysis of the SANS data gives a surface dimension of 2.5 and a surface area comparable to that obtained from the BET analysis. However, the limited range in which power-law behaviour is observed makes conclusions about fractal dimensions and polydispersity questionable.
{"title":"Characterisation of a basal-plane-oriented graphite","authors":"E. Gilbert, P. A. Reynolds, J. White","doi":"10.1039/A801303I","DOIUrl":"https://doi.org/10.1039/A801303I","url":null,"abstract":"We have employed scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), wide-angle X-ray scattering (WAXS), small-angle neutron scattering (SANS) and adsorption isotherms to characterise the recompressed, exfoliated graphite ‘Papyex’. The substrate is found to consist of ca. 60% void space, most of which is associated with galleries with a thickness of ca. 300 A. The substrate contains ca. 70% rhombohedral and 30% hexagonal graphite crystallites with dimensions of the order of several hundred angstroms. We confirm that Papyex has preferentially oriented graphite (0001) planes whose surfaces mainly contribute to the total available surface area. Using the theory of Debye etal., the substrate may be classed as a random two-phase structure. SANS experiments employing contrast variation show that the voids in Papyex are connected and fillable. A Guinier analysis is inappropriate to apply to the present system owing to the large scale and interconnected nature of the void space of the galleries. BET analysis shows Papyex is a non-porous or macroporous material giving a Type II isotherm with a surface area of ca. 20 g−1 and negligible micropores. This suggests that the substrate consists of voids and macroscopic cracks and fissures with dimensions of the order of ca. 500 A or more. Porod analysis of the SANS data gives a surface dimension of 2.5 and a surface area comparable to that obtained from the BET analysis. However, the limited range in which power-law behaviour is observed makes conclusions about fractal dimensions and polydispersity questionable.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"453 1","pages":"1861-1868"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82934575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The application of numerical simulations of temperature-programmed reaction and desorption (TPRD) spectra as a means of supporting mechanistic studies of surface reactions is demonstrated through two simple examples: the chemistry of ethene hydrogenation and the chemistry of methyl moieties co-adsorbed with hydrogen atoms. Where possible, literature kinetic parameters have been employed in the simulations. Where no parameters exist, preliminary estimates of the kinetic parameters were systematically modified until a visual agreement between the empirical TPRD spectra and the numerical simulations was obtained. In this way, these simulations have permitted a preliminary determination of the activation energies and pre-exponential factors for a number of the reaction steps in the chemistry of co-adsorbed methyl moieties and hydrogen atoms.
{"title":"Numerical simulation of temperature-programmed reaction data: an application in surface chemical kinetics","authors":"G. Ellis, J. Sidaway, M. McCoustra","doi":"10.1039/A803766C","DOIUrl":"https://doi.org/10.1039/A803766C","url":null,"abstract":"The application of numerical simulations of temperature-programmed reaction and desorption (TPRD) spectra as a means of supporting mechanistic studies of surface reactions is demonstrated through two simple examples: the chemistry of ethene hydrogenation and the chemistry of methyl moieties co-adsorbed with hydrogen atoms. Where possible, literature kinetic parameters have been employed in the simulations. Where no parameters exist, preliminary estimates of the kinetic parameters were systematically modified until a visual agreement between the empirical TPRD spectra and the numerical simulations was obtained. In this way, these simulations have permitted a preliminary determination of the activation energies and pre-exponential factors for a number of the reaction steps in the chemistry of co-adsorbed methyl moieties and hydrogen atoms.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"2005 1","pages":"2633-2637"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83008647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Datta, D. Mandal, S. Pal, Swati Das, K. Bhattacharyya
The interaction of Triton X-100 (TX) with α- and β-cyclodextrins (CD) has been studied, using 2,6-p-toluidinonaphthalene sulfonate (TNS) as a fluorescent probe, by steady-state and time-resolved emission spectroscopy. The critical micellar concentration (c.m.c.) is indicated by the point of abrupt increase of emission intensity and lifetime of TNS. The apparent c.m.c. increases significantly in the presence of β-CD by as much as 28±1 times at 10 mM β-CD but remains more or less unaffected in the presence of α-CD at similar concentrations. This is attributed to the very strong binding of TX with the large β-CD cavity and negligible binding to the small α-CD. At concentrations below the c.m.c., on addition of TX to aqueous TNS solution containing β-CD the emission intensity decreases. This is ascribed to the competitive binding of TNS and TX with β-CD. This causes displacement of TNS from the CD cavity by the TX surfactant molecules. The binding constant of TX with β-CD is found to be ca. 9400±1300 L mol-1.
以2,6-对甲苯基萘磺酸盐(TNS)为荧光探针，采用稳态和时间分辨发射光谱法研究了Triton X-100 (TX)与α-和β-环糊精(CD)的相互作用。临界胶束浓度(cmcc)由TNS发射强度和寿命的突然增加点表示。在β-CD浓度为10 mM时，β-CD的表观c.m.c.显著增加了28±1倍，但在相似浓度的α-CD存在下，c.m.c.基本不受影响。这是由于TX与大的β-CD腔结合非常强，而与小的α-CD结合可以忽略不计。在低于cmc的浓度下，在含有β-CD的TNS水溶液中加入TX后，发射强度降低。这归因于TNS和TX与β-CD的竞争性结合。这导致TNS被TX表面活性剂分子从CD腔中置换。TX与β-CD的结合常数约为9400±1300 L mol-1。
{"title":"Interaction of Triton X-100 with cyclodextrins. A fluorescence study","authors":"A. Datta, D. Mandal, S. Pal, Swati Das, K. Bhattacharyya","doi":"10.1039/A806868B","DOIUrl":"https://doi.org/10.1039/A806868B","url":null,"abstract":"The interaction of Triton X-100 (TX) with α- and β-cyclodextrins (CD) has been studied, using 2,6-p-toluidinonaphthalene sulfonate (TNS) as a fluorescent probe, by steady-state and time-resolved emission spectroscopy. The critical micellar concentration (c.m.c.) is indicated by the point of abrupt increase of emission intensity and lifetime of TNS. The apparent c.m.c. increases significantly in the presence of β-CD by as much as 28±1 times at 10 mM β-CD but remains more or less unaffected in the presence of α-CD at similar concentrations. This is attributed to the very strong binding of TX with the large β-CD cavity and negligible binding to the small α-CD. At concentrations below the c.m.c., on addition of TX to aqueous TNS solution containing β-CD the emission intensity decreases. This is ascribed to the competitive binding of TNS and TX with β-CD. This causes displacement of TNS from the CD cavity by the TX surfactant molecules. The binding constant of TX with β-CD is found to be ca. 9400±1300 L mol-1.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"2001 1","pages":"3471-3475"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83352610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Daturi, C. Binet, S. Bernal, J. A. P. Omil, J. Lavalley
The effect of two different thermal/chemical pretreatments on a high surface area zirconia sample has been studied using FTIR spectroscopy. As revealed by high resolution electron microscopy (HREM), the sample exhibits a significant concentration of small pores and cavities with size ranging from 1 to 2 nm. When pretreatment 1 was applied, (step-by-step heating under O2 followed by evacuation at increasing temperatures up to 873 K), the oxide appeared clean, and free from impurities detectable by IR spectroscopy. Likewise, no O2− species resulting from further O2 chemisorption at 298 K were observed. In contrast, the IR spectrum for the oxide exposed to pretreatment 2 (heating under O2 at 873 K, followed by fast evacuation at 873 K), shows a number of features that can be interpreted as due to oxalate-like species, as well as adsorbed CO. Additionally, superoxide species could be identified upon O2 chemisorption at room temperature. Further reoxidation treatment at 673 K induces the disappearance of CO features and the transformation of the oxalate-like species. The initial spectrum can be recovered by subsequent evacuation at 873 K, thus indicating the reversible nature of the chemical processes involved. In accordance with the HREM images, we propose that a redox interconversion reaction of chemisorbed species trapped in the oxide cavities is responsible for what we observe on the zirconia sample exposed to pretreatment 2.
{"title":"FTIR study of defects produced in ZrO2 samples by thermal treatment","authors":"M. Daturi, C. Binet, S. Bernal, J. A. P. Omil, J. Lavalley","doi":"10.1039/A708208H","DOIUrl":"https://doi.org/10.1039/A708208H","url":null,"abstract":"The effect of two different thermal/chemical pretreatments on a high surface area zirconia sample has been studied using FTIR spectroscopy. As revealed by high resolution electron microscopy (HREM), the sample exhibits a significant concentration of small pores and cavities with size ranging from 1 to 2 nm. When pretreatment 1 was applied, (step-by-step heating under O2 followed by evacuation at increasing temperatures up to 873 K), the oxide appeared clean, and free from impurities detectable by IR spectroscopy. Likewise, no O2− species resulting from further O2 chemisorption at 298 K were observed. In contrast, the IR spectrum for the oxide exposed to pretreatment 2 (heating under O2 at 873 K, followed by fast evacuation at 873 K), shows a number of features that can be interpreted as due to oxalate-like species, as well as adsorbed CO. Additionally, superoxide species could be identified upon O2 chemisorption at room temperature. Further reoxidation treatment at 673 K induces the disappearance of CO features and the transformation of the oxalate-like species. The initial spectrum can be recovered by subsequent evacuation at 873 K, thus indicating the reversible nature of the chemical processes involved. In accordance with the HREM images, we propose that a redox interconversion reaction of chemisorbed species trapped in the oxide cavities is responsible for what we observe on the zirconia sample exposed to pretreatment 2.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"109 1","pages":"1143-1147"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83353522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The adsorption of ClO4- and SO42- anions on a roughened polycrystalline copper electrode has been studied using surface-enhanced Raman spectroscopy (SERS). It has been found that the ClO4- anion physisorbs at the copper electrode. The chemisorption of the SO42- ion has been revealed both by the large shift of the totally symmetric frequency (from 982 to 967 cm-1) upon adsorption and by the considerable broadening (from 8.5 to 25 cm-1) of the band. The 967 cm-1 band was not sensitive to the solution isotopic H2O–D2O exchange, indicating that sulfate, but not bisulfate, is the adsorbed anion. The same band dominates the spectra of various acidic sulfate solutions in pH region between 0.3 and 4.5. The SER intensity of the adsorbed SO42- ion gradually decreased in the pH range 3–4.5 at a constant electrode potential of -0.20 V, demonstrating the stabilization of SO42- adsorption in more acidic media or the beginning of other processes, such as OH- adsorption or surface oxidation in this pH range.
{"title":"Surface-enhanced Raman spectroscopy of ClO4- and SO42- anions adsorbed at a Cu electrode","authors":"G. Niaura, A. Malinauskas","doi":"10.1039/A800574E","DOIUrl":"https://doi.org/10.1039/A800574E","url":null,"abstract":"The adsorption of ClO4- and SO42- anions on a roughened polycrystalline copper electrode has been studied using surface-enhanced Raman spectroscopy (SERS). It has been found that the ClO4- anion physisorbs at the copper electrode. The chemisorption of the SO42- ion has been revealed both by the large shift of the totally symmetric frequency (from 982 to 967 cm-1) upon adsorption and by the considerable broadening (from 8.5 to 25 cm-1) of the band. The 967 cm-1 band was not sensitive to the solution isotopic H2O–D2O exchange, indicating that sulfate, but not bisulfate, is the adsorbed anion. The same band dominates the spectra of various acidic sulfate solutions in pH region between 0.3 and 4.5. The SER intensity of the adsorbed SO42- ion gradually decreased in the pH range 3–4.5 at a constant electrode potential of -0.20 V, demonstrating the stabilization of SO42- adsorption in more acidic media or the beginning of other processes, such as OH- adsorption or surface oxidation in this pH range.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"16 1","pages":"2205-2211"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90718209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Saielli, A. Polimeno, P. Nordio, P. Bartolini, M. Ricci, R. Righini
The solvation dynamics of the dye Coumarin 503 in the nematic mixture ZLI 1167 has been investigated by means of time-resolved fluorescence spectroscopy, both in the nematic and isotropic phases of the sample. No alignment was imposed on the micro-domains of the nematic phase, so that a complete depolarization of the emitted light was obtained. For the isotropic phase the usual set-up with vertically polarized excitation light and magic-angle detection was used. A time-dependent frequency shift of the maximum of the fluorescence band, caused by solvent reorganization after pulse excitation of the fluorescent probe, was observed. The analysis of the transient Stokes shift correlation function clearly shows biexponential behavior in the nematic phase, the slowest time constant varying from 1670 ps at 311.5 K to 230 ps at 373 K. The decay of the correlation function appears to be largely unaffected by the nematic–isotropic transition, suggesting that the local environment, rather than long-range ordering, determines Stokes shift dynamics. A theoretical model, which takes into account probe reorientations in the presence of a nematic field, and fluctuation of the local solvent polarization, has been developed to interpret the experimental findings.
{"title":"Solvation dynamics of Coumarin 503 in the liquid-crystal mixture ZLI 1167","authors":"G. Saielli, A. Polimeno, P. Nordio, P. Bartolini, M. Ricci, R. Righini","doi":"10.1039/A703999I","DOIUrl":"https://doi.org/10.1039/A703999I","url":null,"abstract":"The solvation dynamics of the dye Coumarin 503 in the nematic mixture ZLI 1167 has been investigated by means of time-resolved fluorescence spectroscopy, both in the nematic and isotropic phases of the sample. No alignment was imposed on the micro-domains of the nematic phase, so that a complete depolarization of the emitted light was obtained. For the isotropic phase the usual set-up with vertically polarized excitation light and magic-angle detection was used. A time-dependent frequency shift of the maximum of the fluorescence band, caused by solvent reorganization after pulse excitation of the fluorescent probe, was observed. The analysis of the transient Stokes shift correlation function clearly shows biexponential behavior in the nematic phase, the slowest time constant varying from 1670 ps at 311.5 K to 230 ps at 373 K. The decay of the correlation function appears to be largely unaffected by the nematic–isotropic transition, suggesting that the local environment, rather than long-range ordering, determines Stokes shift dynamics. A theoretical model, which takes into account probe reorientations in the presence of a nematic field, and fluctuation of the local solvent polarization, has been developed to interpret the experimental findings.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"71 1","pages":"121-128"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89234538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mean reaction field approximation has been developed for Monte Carlo simulation of ion solvation thermodynamics and structure in ion–dipolar systems. Calculations have been carried out for systems having one hard-sphere ion and N-1 hard-sphere dipoles of equal diameter, 256⩽N⩽1372, where N is the number of particles. The reduced charge on the ion, q*, was varied from 0 to 14.15, and two values of the reduced dipole moment, µ*, (1.14 and 1.50) were used for the simulations. The mean reaction field corrections were introduced to take into account the changes in long-range dipole–dipole interactions due to the presence of the ion. The corrections were performed for molecules both inside and outside the truncation sphere, which has an ion at the center, resulting in a small dependence of solvation energy on simulation cell size. Expressions have been developed within the framework of thermodynamic integration and perturbation techniques for calculating the free-energy change on ion charging. The applicability of this approach for simulating the solvation internal energy has been investigated and compared with other methods. The influence of system size and cut-off radius on the thermodynamic solvation parameters and the radial distribution functions were studied. It has been shown that for N500, variation of the simulated system size and cut-off radius does not drastically affect the calculated thermodynamic quantities and radial distribution functions when the mean reaction field corrections were applied. The simulated thermodynamic solvation properties were compared with results found in the literature for various molecular statistical approaches [mean spherical approximation (MSA), linearized hypernetted-chain (LHNC), etc.].
{"title":"Thermodynamics of ion solvation in dipolar solvent using Monte Carlo mean reaction field simulation","authors":"A. Bandura, S. Lvov, D. Macdonald","doi":"10.1039/A706091B","DOIUrl":"https://doi.org/10.1039/A706091B","url":null,"abstract":"The mean reaction field approximation has been developed for Monte Carlo simulation of ion solvation thermodynamics and structure in ion–dipolar systems. Calculations have been carried out for systems having one hard-sphere ion and N-1 hard-sphere dipoles of equal diameter, 256⩽N⩽1372, where N is the number of particles. The reduced charge on the ion, q*, was varied from 0 to 14.15, and two values of the reduced dipole moment, µ*, (1.14 and 1.50) were used for the simulations. The mean reaction field corrections were introduced to take into account the changes in long-range dipole–dipole interactions due to the presence of the ion. The corrections were performed for molecules both inside and outside the truncation sphere, which has an ion at the center, resulting in a small dependence of solvation energy on simulation cell size. Expressions have been developed within the framework of thermodynamic integration and perturbation techniques for calculating the free-energy change on ion charging. The applicability of this approach for simulating the solvation internal energy has been investigated and compared with other methods. The influence of system size and cut-off radius on the thermodynamic solvation parameters and the radial distribution functions were studied. It has been shown that for N500, variation of the simulated system size and cut-off radius does not drastically affect the calculated thermodynamic quantities and radial distribution functions when the mean reaction field corrections were applied. The simulated thermodynamic solvation properties were compared with results found in the literature for various molecular statistical approaches [mean spherical approximation (MSA), linearized hypernetted-chain (LHNC), etc.].","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"14 1","pages":"1063-1072"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89821600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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