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1.
The total and double differential cross sections of the reaction Hg+CsBr→Hg+Cs ++Br − were measured using a molecular-beam technique. The excitation function is similar to that obtained earlier for the collision-induced dissociation of alkali halides by inert gases. The angular distribution of Cs + becomes broader as the collision energy increases. The energy distribution of Cs + at small scattering angles has two distinct peaks which are drawn together as the angle increases. This leads to the horseshoe-like shape of the contour plots (velocity-angle) of the intensity of Cs + scattered. The structure of the double differential cross section is connected with the orientation effects. 相似文献
2.
This study describes a new ion chromatography method using a low-capacity anion exchange column with amperometric and absorbance detection for rapid and simultaneous determination of Br − and NO 3− in contaminated waters where one of these ions is present in excess compared to other. The use of two detectors overcomes the problem of baseline separation for Br − and NO 3− for accurate quantification, which was commonly encountered when using a low-capacity anion exchange column and suppressed conductivity detection mode. The method achieved accurate quantification of these two ions without requirement of baseline separation. The accuracy of 2.8% for NO 3− was determined using a quality control sample obtained from UN GEMS/Water PE Study No. 6. The detection limits for Br − and NO 3− were 20 and 6 μg l −1 (25 μl sample), respectively. Linearity of these two ions was over three orders of magnitude with a correlation coefficient >0.998. The influence of potential interfering ions was also studied followed by the determination of Br − and NO 3− in seawater, unsaturated zone water, soil extract and groundwater. 相似文献
3.
Gaussian-2 ab initio calculations were performed to examine the six modes of unimolecular dissociation of cis-CH 3CHSH + (1 +), trans-CH 3CHSH + (2 +), and CH 3SCH 2+ (3 +): 1 +→CH 3++ trans-HCSH (1); 1 +→CH 3+ trans-HCSH + (2); 1 +→CH 4+HCS + (3); 1 +→H 2+ c-CH 2CHS + (4); 2 +→H 2+CH 3CS + (5); and 3 +→H 2+ c-CH 2CHS + (6). Reactions (1) and (2) have endothermicities of 584 and 496 kJ mol −1, respectively. Loss of CH 4 from 1 + (reaction (3)) proceeds through proton transfer from the S atom to the methyl group, followed by cleavage of the C–C bond. The reaction pathway has an energy barrier of 292 kJ mol −1 and a transition state with a wide spectrum of nonclassical structures. Reaction (4) has a critical energy of 296 kJ mol −1 and it also proceeds through the same proton transfer step as reaction (3), followed by elimination of H 2. Formation of CH 3CS + from 2 + (reaction (5)) by loss of H 2 proceeds through protonation of the methine (C H) group, followed by dissociation of the H 2 moiety. Its energy barrier is 276 kJ mol −1. On both the MP2/6-31G* and QCISD/6-31G* potential-energy surfaces, the H 2 1,1-elimination from 3 + (reaction (6)) proceeds via a nonclassical intermediate resembling c-CH 3SCH 2+ and has a critical energy of 269 kJ mol −1. 相似文献
4.
Rate constants for the tunneling reaction (HD + D → h + D 2) in solid HD increase steeply with increasing temperature above 5 K, while they are almost constant below 4.2 K. The apparent activation energy for the tunneling reaction above 5 K is 95 K, which is consistent with the energy (91–112 K) for vacancy formation in solid hydrogen. The results above 5 K were explained by the model that the tunneling reaction was accelerated by a local motion of hydrogen molecules and hydrogen atoms. The model of the tunneling reaction assisted by the local motion of the reactans and products was applied to the temperature dependence of the proton-transfer tunneling reaction (C 6H 6− + C 2H 5OH → C 6H 7 + C 2H 5O −) in solid ethanol, the tunneling elimination of H 2 molecule of H 2 molecule ((CH 3) 2 CHCH(CH 3) 2+ → (CH 3) 2 C = C(CH 3) 2+ + H 2) in solid 2,3-dimethylbutane, and the selective tunneling reaction of H atoms in solid neo-C 5H 12-alkane mixtures. 相似文献
5.
The gas-phase rapid ion-molecule reaction Si + ( 2P) + NH 3→ SiNH 2+ + H is theoretically investigated by the ab initio molecular orbital methods. Several possible pathways (A, B, C) on its potential energy surface have been examined, discussed and compared. Theoretical calculations indicate that pathway A is favourable in energy and that the reaction begins by forming a collision complex of the ion-dipole molecule Si-NH +3, which forms with no barrier into the first energy well of the reaction coordinate. Migration of an H atom from an N atom to a Si atom forms the intermediate HSi-NH +2, which corresponds to the second energy well and can fragment to the observed product SiNH +2 by losing an H atom from the Si atom. The barriers for migration and fragmentation are 52.5 and 38.6 kcal mol −1 respectively. Pathway A has a negative activation energy of −42.1 kcal mol −1. 相似文献
6.
An ion retarding potential difference (IRPD) method has been used to investigate the ion yield and kinetic energy distributions of N +/N 2 produced by photoionization mass specrometry using synchrotron radiation. Photoion yield curves of energy selected N + ions are deduced. Translational energy distribution of N + at energies of the N(1s)→π*, N(1s)→( nl) 1 and above the N(1s) −1 threshold are determined. Comparison is made with previous photoin-photoelectron coincidence work using time-of-flight (TOF) measurements. 相似文献
7.
Tripodal aza crown ether calix[4]arenes, 5a, 5b, 6a and 6b, have been synthesized. The structure of protonated 5a was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of 5a and 5b towards anions using Na + as countercation were carried out by 1H NMR titration in dimethylsulfoxide- d6 and the mixture of chloroform- d and methanol- d4, respectively. Ligands 5a and 5b were able to form 1:1 complexes with Br −, I − and NO 3− and the complexation stability varied as follows: NO 3−>I −>Br −. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of 5a towards Br − in the presence of various cations varied as K +>Bu 4N +>Na +. The enhancement in anion complexation ability of 5a may result from the rearrangement of the tripodal ammonium unit in the presence of K +. The neutral forms, 6a and 6b, were able to form complexes with transition metal ions such as Co 2+, Ni 2+, Cu 2+ and Zn 2+. The stability of the complexes followed the sequence: Ni 2+2+Cu2+Zn2+. Compounds 6a and 6b may, therefore, potentially be used as either transition metal ion or anion receptors that can be controlled by pH of the solution. 相似文献
8.
This survey begins with the photochemistry at 254 nm and 298 K in the system H 2O 2COO 2RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H 2O + R relative to the well-known rate constant for the reaction OH + CO → CO 2 + H. Inherent in the scheme is that the reaction HO 2+CO→OH+CO 2 is negligible compared with the OH reaction, and a literature consensus gives kHO2 < 10 −19 cm 3 molecule −1 s −1, or some 10 6 less than kOH at 298 K. Theoretical calculations establish that the first stage in the HO 2 reaction is the formation of a free radical intermediate HO 2 + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown. High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, kHO2 = 3.45 × 10−12T1/2 exp(1.15 × 104/T) cm3 molecule−1 s−1, the hard-sphere-collision Arrhenius modification. This yields kHO2(298) = 1.0 × 10−27 cm3 molecule−1 s−1 or some 1014 slower than kOH(298). 相似文献
9.
N 2O gas phase chemistry has been examined as it relates to the problem of ultrathin film silicon oxynitridation for semiconductor devices. Computational and analytical kinetics studies are presented that demonstrate: (i) there are 5 main reactions in the decomposition of N 2O, (ii) the gas composition over a 1000K – 1400K temperature range is as follows: N 2 (65.3 − 59.3%); O 2 (32.0 − 25.7%); NO (2.7 − 15.0%), (iii) the N 2O decomposition obeys first-order kinetics, and the initial rate law for N 2O decomposition is R init = 2k 1[N 2O] which rapidly changes to R late = k 1[N 2O] as the reaction proceeds, (iv) the branching ratio for the two reactions: N 2O + O → 2NO and N 2O + O → N 2 + O 2 lies between 0.1 and 0.5 (0.1 < < 0.5) and varies with conditions, (v) the apparent activation energy for the decomposition of N 2O is 2.5 eV/molecule (2.4×10 2 kJ/mole), (vi) the rate law for NO formation is R = k 1N 2O], and (vii) the apparent activation energy for the formation of NO is 2.4 eV/molecule (2.3×10 2 kJ/mole). 相似文献
10.
This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-( N, N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C 18 column (250×4.6 mm I.D.) coated with 10/10 (m M/m M) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO 3 or Na 2CO 3 aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F −42−−42−2− −3−. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F−42−42−−2− −3−. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F−, HPO42−, Cl−, SO42−, NO2−, Br− and NO3− (S/N=3, sample injection volume 100 μl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 μM, respectively. 相似文献
11.
The reaction of HOCl + HCl → Cl 2 + H 2O in the presence of chlorine anion Cl − has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol −1 and this reaction has been shown to have a high activation barrier of 46.5 kcal mol −1. Cl − is found to catalyze the reaction via the formation of HOCl·Cl −, ClH·HOCl·Cl − and Cl −·H 2) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl. 相似文献
12.
The paper reports results of a study on the specific adsorption of F −, Cl −, Br −, I −, ClO 3−, BrO 3−, IO 3− and IO 4− on hydrous γ-Al 2O 3. The isotherms of the anion adsorption and the adsorption dependencies on pH and the ionic strength of the solution have been determined under the equilibrium conditions. According to the degree of affinity to γ-Al 2O 3, the anions can be ordered as: I −3− −−3−3−4−−. It has been established that the sorption of IO4− and F− involves the formation of surface complexes in the inner co-ordination sphere, whereas that of Cl−, Br−, I−, ClO3−, BrO3− and IO3− takes place through formation of ion pair complexes in the outer co-ordination sphere. In the dynamic system, the exchange isoplanes and elution curves have been determined for selected anions on columns filled with Al2O3. It has been shown that γ-Al2O3 can be used for isolation and concentration of IO3− from natural waters in order to decrease the limit of the ions determination to 2 μg l−1. Using differential pulse voltammetry (DPV), after isolation and concentration on γ-Al2O3, the content of iodates has been determined in mineral, marine and tap water doped with these ions. 相似文献
13.
Proton magnetic resonance spectra have been studied over a wide temperature range for polycrystalline ethyltrimethylammonium halides [C 2H 3N(CH 3) 3] +X −, where X − = Cl −, Br − and I −. For the bromide and its ethyl-deuterated analogue, the proton relaxation times T1 were also measured vs. temperature. Analysis of the experimental data yields information on the activation parameters for molecular motion within the cation and of the cation as a whole. The potential barriers determined increase as anion size decreases. 相似文献
14.
A new molecular tweezer receptor Hc1 based on hyodeoxycholic acid has been synthesized and its binding properties were accessed by 1H NMR and isothermal titration calorimetry experiments. Molecular tweezer Hc1 shows a high selectivity toward F − over Cl −, Br −, I −, and H 2PO 4−. 相似文献
16.
CaSiO3:Eu0.08^3+Bi0.002^3+ with a monoclinic perovskite structure was synthesized by using sol-gel method, and its luminescence characteristics were investigated. From the excitation spectrum, it can be seen that the main peaks located at 238,396,415,437 and 359 nm correspond to the charge-transfer band of Eu^3+-O^2- , the absorption transitions of ^7F0.1→^3L6, ^7F0→^5D3, ^7F1→^5D3 of Eu^3+ ions, and ^3P1→^1S0 of Bi^3+ ions, respectively. When the samples were excited with a light of wavelength 359 or 395 nm, it can be seen from the emission spectrum that the electronic dipole transition located at 609 nm corresponding to ^5D0→^7F2 of Eu^3+ ions was stronger than the magnetic dipole transition located at 587 nm corresponding to ^5D0→^7F1 of Eu^3+ ions, which shows that more Eu^3+ ions were located in nonreversion center lattices. The energy transfer from Bi^3+ ions to Eu^3+ ions in the phosphor was also discussed. The results show that Eu^3+ ions could be well sensitized by ^3+ions, and the energy-transfer pattern between Bi^3+ ions and Eu^3+ ions was resonance energy transfer. 相似文献
17.
The redox reaction between bromate and chloride ions in the presence and the absence of two or less equivalents of bromide ion ascertaining the formation of bromine chloride species of type BrCl and BrCl 2− in subsequent reactions in 4% H 2SO 4, has been studied by spectrophotometry. Calibration graphs for the bromide ion estimation in 0.1% KBrO 3–4% H 2SO 4 medium are determined separately in the presence of known amounts of NaCl. The effect of Cl − ion percentage on the determination of Br − ion is studied and reported herewith a suitable equation for a precise, reliable and quick spectrophotometric estimation. 相似文献
18.
The reaction of trans-X(CO) 4WCNR 2 (X = Br, R = c hex (cyclohexyl); X = Cl, R = c hex, ipr (isopropyl) with M +X − (M + = NEt 4+, X − = Br −; M + = PPN +, X − = Cl −) leads under substitution of one CO ligand to new anionic dihalo(tricarbonyl)carbyne-tungsten complexes of the type M + mer-[(X) 2(CO) 3WCNR 2] − (M + = NEt 4+, X = Br, R = c hex; M + = PPN +, X = Cl, R = c hex, i pr), whose composition and structure were determined by elemental analysis as well as by IR, 1H and 13C NMR spectroscopy. In the anionic carbyne complexes the entered halogen ligand, coordinated in a cis position relative to the carbyne ligand on the metal, can be easily substituted by neutral nucleophiles, as the reaction of PPN + mer-[(Cl) 2(CO) 3WCN chex 2] − with PPh 3 demonstrates yielding the neutral carbyne complex mer-[Cl(CO) 3(PPh 3)WCN chex 2]. 相似文献
19.
The rate coefficients of the reactions: (1) CN + H 2CO → products and (2) NCO + H 2CO → products in the temperature range 294–769 K have been determined by means of the laser photolysis-laser induced fluorescence technique. Our measurements show that reaction (1) is rapid: k1(294 K) = (1.64 ± 0.25) x 10 −11 cm 3 molecule −1 s −1; the Arrhenius relation was determined as k1 = (6.7 ± 1.0) x 10 −11 exp[(−412 ± 20)/T] cm 3 molecule −1 s −1. Reaction (2) is approximately a tenth as rapid as reaction (1) and the temperature dependence of k2 does not conform to the Arrhenius form: k2 = 4.62 x 10 −17T1.71 exp(198/ T) cm 3 molecule −1 s −1. Our values are in reasonable agreement with the only reported measurement of k1; the rate coefficients for reaction (2) have not been previously reported. 相似文献
20.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
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