A flow-mixing calorimeter has been used to measure the excess molar enthalpy HmE of (cyclohexane+chloroform)(g) and (benzene+chloroform)(g) at standard atmospheric pressure over the temperature range 353.2–423.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the chloroform using the Stockmayer potential. Cross-terms were calculated using the equation e12=(1-k12)(e11e22)1/2 and to fit the measurements on (cyclohexane+chloroform)(g) the value (1-k12)=0.965 was needed. This value was used to calculate HmE for (benzene+chloroform)(g), and the calculated values were found to be positive and to be similar to those for (cyclohexane+chloroform)(g). However, the experimental values are negative, and about 35 J mol-1 below the values for (cyclohexane+chloroform)(g). The difference between the calculated and experimental values was described in terms of a quasi-chemical model that, for the benzene–chloroform interaction, yielded a value of the equilibrium constant K12(298.15 K)=0.373 MPa-1 and an enthalpy of association ΔH12=-(16.1±2) kJ mol-1. This value of ΔH12 is attributed to a charge transfer between the benzene and the chloroform that is not present in the cyclohexane–chloroform interaction.
{"title":"Benzene–chloroform association Excess molar enthalpy of (cyclohexane+chloroform)(g) and (benzene+chloroform)(g) at temperatures from 353.2 to 423.2 K","authors":"C. Wormald, P. Johnson","doi":"10.1039/A708601F","DOIUrl":"https://doi.org/10.1039/A708601F","url":null,"abstract":"A flow-mixing calorimeter has been used to measure the excess molar enthalpy HmE of (cyclohexane+chloroform)(g) and (benzene+chloroform)(g) at standard atmospheric pressure over the temperature range 353.2–423.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the chloroform using the Stockmayer potential. Cross-terms were calculated using the equation e12=(1-k12)(e11e22)1/2 and to fit the measurements on (cyclohexane+chloroform)(g) the value (1-k12)=0.965 was needed. This value was used to calculate HmE for (benzene+chloroform)(g), and the calculated values were found to be positive and to be similar to those for (cyclohexane+chloroform)(g). However, the experimental values are negative, and about 35 J mol-1 below the values for (cyclohexane+chloroform)(g). The difference between the calculated and experimental values was described in terms of a quasi-chemical model that, for the benzene–chloroform interaction, yielded a value of the equilibrium constant K12(298.15 K)=0.373 MPa-1 and an enthalpy of association ΔH12=-(16.1±2) kJ mol-1. This value of ΔH12 is attributed to a charge transfer between the benzene and the chloroform that is not present in the cyclohexane–chloroform interaction.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"11 1","pages":"1267-1270"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73112506","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 pH-dependent structural transformations in aqueous solutions of natural and synthetic flavylium salts are re-examined. The procedure uses Malvin as a reference compound and exploits the different timescales of the kinetic process that take place prior to the equilibration. For each process a kinetic expression was deduced allowing calculation of all the equilibrium constants and most of the rate constants of the system. The equilibrium constants were confirmed by comparison with the data obtained by 1H NMR. Clear evidence for the formation of significant amounts of trans-chalcone in Malvin was obtained.
{"title":"Thermodynamics and kinetics of flavylium salts Malvin revisited","authors":"F. Pina","doi":"10.1039/A802602E","DOIUrl":"https://doi.org/10.1039/A802602E","url":null,"abstract":"The pH-dependent structural transformations in aqueous solutions of natural and synthetic flavylium salts are re-examined. The procedure uses Malvin as a reference compound and exploits the different timescales of the kinetic process that take place prior to the equilibration. For each process a kinetic expression was deduced allowing calculation of all the equilibrium constants and most of the rate constants of the system. The equilibrium constants were confirmed by comparison with the data obtained by 1H NMR. Clear evidence for the formation of significant amounts of trans-chalcone in Malvin was obtained.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"40 1","pages":"2109-2116"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75583734","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}
(VO)3(PO4)2·7H2O and (VO)3(PO4)2·9H2O vanadyl(IV) orthophosphate hydrates (V/P = 1.5) used as precursor compounds were transformed into highly active ammoxidation catalysts during different pretreatment procedures. These structural transformations have been investigated in the presence of ammonia-containing gases or under nitrogen, leading into materials that contain crystalline (NH4)2(VO)3(P2O7)2 (V/P = 0.75) and (VO)2P2O7 (V/P = 1) specimens, respectively, as well as an additional X-ray-amorphous phase of partially crystalline vanadium oxides. These vanadium oxides represent the molar vanadium excess of the original precursor material in comparison to the defined vanadium amount of the crystalline proportion of the transformation product. Both components of these solids are tightly grown together to form microdomains. The solids generated this way were characterized by XRD, EDX, FTIR spectroscopy, 31P MAS NMR spectroscopy, XPS and chemical analyses and used as catalysts in the ammoxidation of toluene to benzonitrile. The results of the heterogeneous catalytic ammoxidation on the orthophosphate derived catalysts were compared with those runs obtained by the application of pure, as-synthesized (NH4)2(VO)3(P2O7)2, similar transformation products derived from VOHPO4·0.5H2O precursor (V/P = 1) and pure (VO)2P2O7. Owing to the existence of mixed-valent vanadium oxides in increased portions of the orthophosphate derived catalysts, these solids reveal a significant enhancement of the toluene conversion rate at almost equal high nitrile selectivities in comparison to usual VPO catalysts.
{"title":"Enhancement of the catalytic activity of VPO ammoxidation catalysts by use of vanadyl(IV) orthophosphate precursor compounds","authors":"Andreas Martin, G. Wolf, U. Steinike, B. Lücke","doi":"10.1039/A801531G","DOIUrl":"https://doi.org/10.1039/A801531G","url":null,"abstract":"(VO)3(PO4)2·7H2O and (VO)3(PO4)2·9H2O vanadyl(IV) orthophosphate hydrates (V/P = 1.5) used as precursor compounds were transformed into highly active ammoxidation catalysts during different pretreatment procedures. These structural transformations have been investigated in the presence of ammonia-containing gases or under nitrogen, leading into materials that contain crystalline (NH4)2(VO)3(P2O7)2 (V/P = 0.75) and (VO)2P2O7 (V/P = 1) specimens, respectively, as well as an additional X-ray-amorphous phase of partially crystalline vanadium oxides. These vanadium oxides represent the molar vanadium excess of the original precursor material in comparison to the defined vanadium amount of the crystalline proportion of the transformation product. Both components of these solids are tightly grown together to form microdomains. The solids generated this way were characterized by XRD, EDX, FTIR spectroscopy, 31P MAS NMR spectroscopy, XPS and chemical analyses and used as catalysts in the ammoxidation of toluene to benzonitrile. The results of the heterogeneous catalytic ammoxidation on the orthophosphate derived catalysts were compared with those runs obtained by the application of pure, as-synthesized (NH4)2(VO)3(P2O7)2, similar transformation products derived from VOHPO4·0.5H2O precursor (V/P = 1) and pure (VO)2P2O7. Owing to the existence of mixed-valent vanadium oxides in increased portions of the orthophosphate derived catalysts, these solids reveal a significant enhancement of the toluene conversion rate at almost equal high nitrile selectivities in comparison to usual VPO catalysts.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"49 1","pages":"2227-2233"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75728139","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 origin of chemical anisotropy in the dissolution of single-crystal silicon in alkaline solutions is discussed in terms of the atomic configuration of silicon in the pentacoordinated transition state for (100) and (111) surfaces. It is proposed that tetravalent silicon, which is bonded in a tetrahedral geometry, is attacked in the etch process by the hydroxide ion, forming a pentacoordinated transition state. Owing to the number of bond angles that are fixed by the atomic arrangement at the surface, the energetically favoured trigonal bipyramidal geometry for a pentacoordinated complex is only slightly distorted for the former plane but significantly distorted for the latter, resulting in a higher activation energy for the dissolution of (111) surfaces. The difference in the activation energies for the dissolution of Si(100) and (111) surfaces, arising from steric hindrance in the transition state, can be estimated from the activation energy for a pseudo-rotation of a similar system.
{"title":"Mechanistic aspects of anisotropic dissolution of materials Etching of single-crystal silicon in alkaline solutions","authors":"T. Baum, D. Schiffrin","doi":"10.1039/A707473E","DOIUrl":"https://doi.org/10.1039/A707473E","url":null,"abstract":"The origin of chemical anisotropy in the dissolution of single-crystal silicon in alkaline solutions is discussed in terms of the atomic configuration of silicon in the pentacoordinated transition state for (100) and (111) surfaces. It is proposed that tetravalent silicon, which is bonded in a tetrahedral geometry, is attacked in the etch process by the hydroxide ion, forming a pentacoordinated transition state. Owing to the number of bond angles that are fixed by the atomic arrangement at the surface, the energetically favoured trigonal bipyramidal geometry for a pentacoordinated complex is only slightly distorted for the former plane but significantly distorted for the latter, resulting in a higher activation energy for the dissolution of (111) surfaces. The difference in the activation energies for the dissolution of Si(100) and (111) surfaces, arising from steric hindrance in the transition state, can be estimated from the activation energy for a pseudo-rotation of a similar system.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"2016 18","pages":"691-694"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72608076","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}
Diffusion processes of the intermediate radicals created by the photochemical reactions of ketones in alcoholic solvents are investigated by using the transient grating (TG) method. The electrically neutral radicals and the anion radicals of acetophenone, benzaldehyde, xanthone, benzophenone and benzil were created selectively by controlling the concentration of sodium hydroxide (NaOH) in alcoholic solvents. The translational diffusion constants (D) of the anion radicals, the neutral radicals, and the parent stable molecules can be successfully measured under the same conditions by this method. It is found that both the neutral and anion radicals diffuse slower than the parent molecules. Values of D of the anion radicals, the neutral radicals and the parent molecules are compared in detail in wide ranges of solvent viscosities, solute sizes and temperatures. Under any conditions, D values of the charged radicals are similar to those of the neutral radicals. A possible origin of such a similarity is discussed in term of the intermolecular charge polarizabilities of the radicals.
{"title":"Diffusion of electrically neutral radicals and anion radicals created by photochemical reactions","authors":"K. Okamoto, N. Hirota, and Masahide Terazima","doi":"10.1039/A706220F","DOIUrl":"https://doi.org/10.1039/A706220F","url":null,"abstract":"Diffusion processes of the intermediate radicals created by the photochemical reactions of ketones in alcoholic solvents are investigated by using the transient grating (TG) method. The electrically neutral radicals and the anion radicals of acetophenone, benzaldehyde, xanthone, benzophenone and benzil were created selectively by controlling the concentration of sodium hydroxide (NaOH) in alcoholic solvents. The translational diffusion constants (D) of the anion radicals, the neutral radicals, and the parent stable molecules can be successfully measured under the same conditions by this method. It is found that both the neutral and anion radicals diffuse slower than the parent molecules. Values of D of the anion radicals, the neutral radicals and the parent molecules are compared in detail in wide ranges of solvent viscosities, solute sizes and temperatures. Under any conditions, D values of the charged radicals are similar to those of the neutral radicals. A possible origin of such a similarity is discussed in term of the intermolecular charge polarizabilities of the radicals.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"68 1","pages":"185-194"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74798622","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}
Progressive CO adsorption has been studied by IR spectroscopy, at low temperature on acid-leached steamed Y zeolites and on two silica–alumina samples with different Si/Al ratios. The IR spectra of the steamed Y zeolites are complex in the ν(OH) range. After CO adsorption only some perturbed ν(OH) and ν(CO) bands had previously been assigned. This study showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica–alumina samples, allowing us to relate them to silica–alumina debris. On the silica–alumina samples, the more acidic site strength [characterized by a perturbed ν(OH) band near 3450 cm-1] was found to be close to that of the high-frequency (HF)OH groups of non-dealuminated HY zeolites. A quantitative estimation of such sites was obtained by determination of the molar absorption coefficient e(CO) of the corresponding perturbed ν(CO) band.
{"title":"Brnsted acidity of extraframework debris in steamed Y zeolites from the FTIR study of CO adsorption","authors":"O. Cairon, J. Lavalley","doi":"10.1039/A803886D","DOIUrl":"https://doi.org/10.1039/A803886D","url":null,"abstract":"Progressive CO adsorption has been studied by IR spectroscopy, at low temperature on acid-leached steamed Y zeolites and on two silica–alumina samples with different Si/Al ratios. The IR spectra of the steamed Y zeolites are complex in the ν(OH) range. After CO adsorption only some perturbed ν(OH) and ν(CO) bands had previously been assigned. This study showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica–alumina samples, allowing us to relate them to silica–alumina debris. On the silica–alumina samples, the more acidic site strength [characterized by a perturbed ν(OH) band near 3450 cm-1] was found to be close to that of the high-frequency (HF)OH groups of non-dealuminated HY zeolites. A quantitative estimation of such sites was obtained by determination of the molar absorption coefficient e(CO) of the corresponding perturbed ν(CO) band.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"2 1","pages":"3039-3047"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78594075","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}
It has been demonstrated by microcalorimetric and fast reaction techniques that D-ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) from spinach shows strong and weak binding sites for the substrate D-ribulose 1,5-bisphosphate (RuBP), for the effector 6-D-phosphogluconate (6-PG), and for the so called ‘transition state analogue’ 2-carboxy-D-arabinitol 1,5-bisphosphate (CABP). The stoichiometry n, the dissociation constant Kd and the enthalpy change ΔHb associated with the strong binding of RuBP and CABP to RUBISCO were measured by isothermal differential titration calorimetry. In addition, differential scanning calorimetry showed an increase of the thermal stability of RUBISCO in the presence of RuBP, 6-PG and especially CABP. The kinetics of binding of RuBP and 6-PG to RUBISCO were measured by stopped flow and iodine laser temperature jump experiments using the fluorescence probe 2-(p-toluidinyl)naphthalene-6-sulfonate. The kinetics of the reversible bimolecular binding reactions of RuBP and 6-PG revealed a fast and a slow phase corresponding to the strong and weak ligand binding phenomena observed in equilibrium measurements. The association and dissociation rate constants k+ and k- for these processes were determined. The dissociation constants Kd calculated from the kinetic constants are in good agreement with Kd values obtained from calorimetric and fluorescence titration studies.
通过微量热法和快速反应技术证明，菠菜中的d -核酮糖1,5-二磷酸羧化酶/加氧酶(RUBISCO)对底物d -核酮糖1,5-二磷酸(RuBP)、效应物6- d -磷酸葡萄糖酸盐(6-PG)和所谓的“过渡态类似物”2-羧基d -阿拉伯糖醇1,5-二磷酸(CABP)具有强弱结合位点。用等温差示滴定量热法测定了RuBP和CABP与RUBISCO强结合的化学计量n、解离常数Kd和焓变ΔHb。此外，差示扫描量热法显示RuBP、6-PG，尤其是CABP的存在使RUBISCO的热稳定性提高。采用荧光探针2-(对甲苯基)萘-6-磺酸盐，通过停流实验和碘激光温度跳变实验测量了RuBP和6-PG与RUBISCO的结合动力学。RuBP和6-PG的可逆双分子结合反应动力学显示出与平衡测量中观察到的强配体结合和弱配体结合相对应的快、慢相。测定了这些反应的缔合速率常数k+和k-。从动力学常数计算的解离常数Kd与从量热法和荧光滴定法研究得到的Kd值很一致。
{"title":"Thermodynamics and kinetics of sugar phosphate binding to D-ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO)","authors":"J. Frank, J. Vater, J. Holzwarth","doi":"10.1039/A802124D","DOIUrl":"https://doi.org/10.1039/A802124D","url":null,"abstract":"It has been demonstrated by microcalorimetric and fast reaction techniques that D-ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) from spinach shows strong and weak binding sites for the substrate D-ribulose 1,5-bisphosphate (RuBP), for the effector 6-D-phosphogluconate (6-PG), and for the so called ‘transition state analogue’ 2-carboxy-D-arabinitol 1,5-bisphosphate (CABP). The stoichiometry n, the dissociation constant Kd and the enthalpy change ΔHb associated with the strong binding of RuBP and CABP to RUBISCO were measured by isothermal differential titration calorimetry. In addition, differential scanning calorimetry showed an increase of the thermal stability of RUBISCO in the presence of RuBP, 6-PG and especially CABP. The kinetics of binding of RuBP and 6-PG to RUBISCO were measured by stopped flow and iodine laser temperature jump experiments using the fluorescence probe 2-(p-toluidinyl)naphthalene-6-sulfonate. The kinetics of the reversible bimolecular binding reactions of RuBP and 6-PG revealed a fast and a slow phase corresponding to the strong and weak ligand binding phenomena observed in equilibrium measurements. The association and dissociation rate constants k+ and k- for these processes were determined. The dissociation constants Kd calculated from the kinetic constants are in good agreement with Kd values obtained from calorimetric and fluorescence titration studies.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"62 1","pages":"2127-2133"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75092807","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}
S. Picard, A. Canosa, B. Rowe, R. Brownsword, I. Smith
The pulsed laser photolysis, time-resolved laser-induced fluorescence technique has been implemented in a CRESU (Cine′tiquedeRe′actionenEcoulementSupersoniqueUniforme) apparatus to measure the rates of the association reactions of CH radicals with N2 and CO at 53 K and five different densities of the carrier gas Ar. The pressure-dependent rate constants have been combined with those reported previously for the temperature range 202⩽T/K⩽584 (R. A. Brownsword, L. B. Herbert, I. W. M. Smith and D. W. A. Stewart, J. Chem. Soc., FaradayTrans., 1996, 92, 1087) to yield, via a global fitting procedure, the following expressions for the two rate constants in the limit of low pressure: These expressions are very similar to those deduced previously by Brownsword etal., demonstrating that the analysis of rate constants for association reactions by the methods proposed by Troe (J. Chem. Phys., 1977, 66, 4758) can be applied over a wide range of temperature. These low temperature kinetic data, especially those for CH+N2, have some relevance to the chemistry of the atmospheres of some planets and planetary moons.
脉冲激光光解、时间分辨激光诱导荧光技术在CRESU (Cine 'tiquedeRe ' actionenecoulementsupersonique均匀)装置上实现，测量了53 K和5种不同密度载气Ar下CH自由基与N2和CO的缔合反应速率。压力相关速率常数已与先前报道的温度范围202≤T/K≤584的速率常数相结合(R. a . Brownsword, L. B. Herbert，I. W. M. Smith和D. W. A. Stewart, J. Chem。Soc。, FaradayTrans。(1996, 92, 1087)，通过全局拟合程序，得到低压极限下两个速率常数的如下表达式:这些表达式与Brownsword etal先前推导的表达式非常相似。证明了用Troe (J. Chem.)提出的方法分析缔合反应的速率常数。理论物理。(1977,66,4758)可适用于很宽的温度范围。这些低温动力学数据，特别是关于CH+N2的数据，与一些行星和行星卫星的大气化学有一定的相关性。
{"title":"Determination of the limiting low pressure rate constants of the reactions of CH with N2 and CO: a CRESU measurement at 53 K","authors":"S. Picard, A. Canosa, B. Rowe, R. Brownsword, I. Smith","doi":"10.1039/A803930E","DOIUrl":"https://doi.org/10.1039/A803930E","url":null,"abstract":"The pulsed laser photolysis, time-resolved laser-induced fluorescence technique has been implemented in a CRESU (Cine′tiquedeRe′actionenEcoulementSupersoniqueUniforme) apparatus to measure the rates of the association reactions of CH radicals with N2 and CO at 53 K and five different densities of the carrier gas Ar. The pressure-dependent rate constants have been combined with those reported previously for the temperature range 202⩽T/K⩽584 (R. A. Brownsword, L. B. Herbert, I. W. M. Smith and D. W. A. Stewart, J. Chem. Soc., FaradayTrans., 1996, 92, 1087) to yield, via a global fitting procedure, the following expressions for the two rate constants in the limit of low pressure: These expressions are very similar to those deduced previously by Brownsword etal., demonstrating that the analysis of rate constants for association reactions by the methods proposed by Troe (J. Chem. Phys., 1977, 66, 4758) can be applied over a wide range of temperature. These low temperature kinetic data, especially those for CH+N2, have some relevance to the chemistry of the atmospheres of some planets and planetary moons.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"14 1","pages":"2889-2893"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72680039","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}
Estimates are made, by using BHandHLYP/6-311G** density functional molecular orbital theory, of the activation energies and frequency factors for a series of intramolecular hydrogen-atom abstraction reactions in aliphatic peroxyl radicals.
{"title":"Self-abstraction in aliphatic hydroperoxyl radicals","authors":"Wai-To Chan, I. Hamilton, H. O. Pritchard","doi":"10.1039/A803344G","DOIUrl":"https://doi.org/10.1039/A803344G","url":null,"abstract":"Estimates are made, by using BHandHLYP/6-311G** density functional molecular orbital theory, of the activation energies and frequency factors for a series of intramolecular hydrogen-atom abstraction reactions in aliphatic peroxyl radicals.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"26 1","pages":"2303-2306"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77348718","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 depletion kinetics of excited-state Cr(a5DJ, a5S2) upon interaction with O2, NO, and N2 have been studied in a discharged flow reactor at He pressures of 0.5 and 0.7 Torr. The interaction with N2 showed no depletion of Cr(a5DJ, a5S2) but an increase in populations of these states. This was attributed to relaxation of higher lying excited states to Cr(a5DJ, a5S2). For the interactions with NO, the depletion rate constants are (115 ± 29) × 10−12 cm3 s−1 (over all J levels) and (36 ± 4) × 10−12 cm3 s−1 for Cr(a5DJ) and Cr(a5S2), respectively. The depletion rate constants for Cr(a5DJ) and Cr(a5S2) by O2 are (62 ± 14) × 10−12 cm3 s−1 (over all J levels) and (27 ± 11) × 10−12 cm3 s−1 respectively. Although the former is a factor of two larger, this difference is much smaller than the difference in the depletion rate constants for the same electronic states of Mo, another Group 6 metal atom. These results were discussed by schematic potential curves where ionic surfaces play an important role.
{"title":"Kinetics of excited-state Cr(a5DJ, a5S2) depletion by O2, NO, and N2","authors":"C. Haynes, K. Honma","doi":"10.1039/A800201K","DOIUrl":"https://doi.org/10.1039/A800201K","url":null,"abstract":"The depletion kinetics of excited-state Cr(a5DJ, a5S2) upon interaction with O2, NO, and N2 have been studied in a discharged flow reactor at He pressures of 0.5 and 0.7 Torr. The interaction with N2 showed no depletion of Cr(a5DJ, a5S2) but an increase in populations of these states. This was attributed to relaxation of higher lying excited states to Cr(a5DJ, a5S2). For the interactions with NO, the depletion rate constants are (115 ± 29) × 10−12 cm3 s−1 (over all J levels) and (36 ± 4) × 10−12 cm3 s−1 for Cr(a5DJ) and Cr(a5S2), respectively. The depletion rate constants for Cr(a5DJ) and Cr(a5S2) by O2 are (62 ± 14) × 10−12 cm3 s−1 (over all J levels) and (27 ± 11) × 10−12 cm3 s−1 respectively. Although the former is a factor of two larger, this difference is much smaller than the difference in the depletion rate constants for the same electronic states of Mo, another Group 6 metal atom. These results were discussed by schematic potential curves where ionic surfaces play an important role.","PeriodicalId":17286,"journal":{"name":"Journal of the Chemical Society, Faraday Transactions","volume":"60 1","pages":"1171-1177"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80192419","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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