Relaxation of vibrationally excited HCl in solid Xe

Rates for vibrational relaxation of HCl(ν = 1.2) in solid xenon at 40 and 146 K are reported and are compared to the rate of relaxation of HCl(ν = 1) in liquid xenon near the freezing point. Upon freezing, the rate of relaxation of HCl(ν = 1) is found to decrease significantly and emission from HCl(ν = 2), absent in the liquid phase, is detected. Both of these effects are attributed to a significant decrease in mobility of HCl molecules in the solid phase as compared to the liquid phase. At both 40 and 146 K, the ratio of relaxation rates for HCl(ν = 2) to HCl(ν = 1) is found to deviate significantly from the harmonic oscillator prediction of 2:1. The rate of relaxation for HCl(ν = 1) by xenon is found to be similar in both liquid solution at 200 K and in the solid at 146 K.     

Effect of vibrational excitation on the collisional removal of free radicals by atoms: OH(upsilon=1) + N

The collisional removal of vibrationally excited OH(upsilon=1) by N(4S) atoms is investigated. The OH radical was prepared by 193 nm photolysis of H2O2, and N(4S) atoms were generated by a microwave discharge in N2 diluted in argon. The concentrations of OH(upsilon=0 and 1) were monitored by laser-induced fluorescence as a function of the time after the photolysis laser pulse. The N(4S) concentration was determined from the OH(upsilon=0) decay rate, using the known rate constant for the OH(upsilon=0) + N(4S) --> H + NO reaction. From comparison of the OH(upsilon=0 and 1) decay rates, the ratio of the rate constant k(upsilon=1)(OH-N) for removal of OH(upsilon=1) in collisions with N(4S) and the corresponding OH(upsilon=0) rate constant, k(upsilon=0)(OH-N) was determined to be 1.61 +/- 0.42, yielding k(upsilon=1)(OH-N) = (7.6 +/- 2.1) x 10(-11) cm3 molecule(-1) s(-1), where the quoted uncertainty (95% confidence limits) includes the uncertainty in k(upsilon=0)(OH-N). Thus, the collisional removal of OH(upsilon=1) by N(4S) atoms is found to be faster than for OH(upsilon=0).     

Quantum transition state theory for the full three-dimensional H+H2 reaction

A recently developed quantum transition state theory (QTST) [E. Pollak and J. L. Liao, J. Chem. Phys. 108, 2733 (1998)] for calculating thermal rate constants of chemical reactions is applied to the full three-dimensional hydrogen exchange reaction. Results are compared with other numerical results, for temperatures ranging from T=300 K to T=1500 K. The QTST rate is almost exact at high temperature and is 20% greater than the exact rate at T=300 K, where there is extensive tunneling.     

BLEACHING OF PURPLE MEMBRANE WITH O-SUBSTITUTED HYDROXYLAMINES

Abstract The retinal Schiff base of bacteriorhodopsin, in the purple membrane from Halobacterium halobium , can be cleaved by hydroxylamine in the presence of light. We have further investigated this reaction with a series of O -substituted hydroxylamines, RONH₂, where R = -H (HA), -CH₃ (MHA), -SO₃− (HAS), benzyl- (BHA), p -nitrobenzyl- (NBHA), and pentafluorobenzyl- (FBHA). All except MHA caused light-induced bleaching of the purple membrane and the chromophore could be regenerated from apomembrane and all- trans retinal. Relative bleaching rate constants were obtained from V = QI _a k ₀ X /( k _r+ k ₀ X ), where V = bleaching rate, Q = quantum yield, I a = absorbed light intensity, X = hydroxylamine concentration, k ₀= rate constant for bleaching and k _r= rate constant for return of photoexcited bacteriorhodopsin to the initial state. This equation fits the time-, concentration- and intensity-dependences of the bleaching reactions in 0.02 M phosphate, pH 7.0. The rate constants k ₀ relative to HA were: MHA: 0; HAS: 0.3; HA: 1.0; BHA: 1.8; FBHA: 10.1; NBHA: 10.8. The relative rate constants do not correlate with the basicity of the derivatives. Instead, the results suggest that the retinal Schiff base is near a non-polar cavity into which an aromatic group can be inserted.     

Temperature dependence of the vibrational deactivation of NO(ν = 1) and NO(ν = 2) by NO

The temperature dependence of the vibrational relaxation of NO(ν = 1) and NO(ν = 2) by NO has been investigated over the range 220–470K. The vibrationally excited NO was produced by the pulse radiolysis of dilute NO-Ar mixtures and temporal dependence of the NO(ν = 1) and NO(ν = 2) followed by UV absorption spectrophotometry. The results for the self-relaxation of NO(ν = 1) are in good agreement with previous measurements exhibiting a minimum in the relaxation rate constant near 300 K; however, the results for the V-V exchange between NO(ν = 2) and NO(ν = 0) are approximately a factor of two smaller that the results calculated from the relaxation rate constant of the reverse 1+1 process and detailed balance at 300 K. The temperature dependence of the V-V exchange rate constant is in good agreement with calculated estimates based on Rapp's SSH theory for V-V transfer. The long-range dipole-dipole formulation must be extended to other than ¹Σ state systems in order to explicitly take into account the influence of spin-orbit coupling on the state-to-state rate constants for vibrational relaxation.     

ESR spectroscopic study on the addition of PhCONHCHCO2Me radicals to alkenes and spin traps

Using ESR spectroscopy, the rate constants for the addition of PhCONHCHCO₂Me radicals to alkenes CH₂=CXY (X = Me, Y = Ph; X = H, Y = Ph; X = Me, Y = CO₂Me; X = H, Y = CO₂Me; X = H, Y = CN) and nitrosodurene were determined at 22 °C. It is shown that a linear dependence exists between the donor-acceptor properties of the substituents at the vinyl group and the rate constants for the addition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2124–2126, August, 1996.     

Direct measurement and theoretical calculation of the rate coefficient for Cl+CH3 in the range from T=202-298 K

The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 association reaction at T=202, 250, and 298 K and P=0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]0=9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T=202 K, the rate coefficient increases from 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-1. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K.     

硫酸铝渣制备聚硅酸铝铁絮凝剂及应用性能研究

以硫酸铝渣为原料,研制出了一系列不同A1／Fe／Si物质的量比的聚硅酸铝铁絮凝剂（简称PAFsc）。考察了PAFSC的混凝、除浊、脱色等性能,并研究了A1／Fe／Si物质的量比、pH、投药量等因素对PAFSC性能的影响。处理模拟浊水时,当n（A1）／n（Fe）=2．0～4．0,n（M）／n（SiO2）=0．7～1．3时...     

Kinetics of the nucleophilic substitution of benzyl-tributylammonium bromide with allyl,butyl, and benzyl chlorides and with benzyl acetate and benzyl ether

In this study, we investigated the kinetics of the nucleophilic substitutions, RX + (BzBu₃NBr) ← → RBr + (BzBu₃NX), where R = allyl, Bu and Bz, when X = Cl; and X = AcO and BzO when R = Bz. The forward and backward rate constants in addition to the activation energies for R = allyl and Bu were also determined. However, only the rate constants at 35°C were determined for the benzyl compounds with toluene as the solvent to reduce the reaction rate. Moreover, the effects of the structures of the groups R and the leaving groups X on the reactivity were compared. Results in this study can provide valuable information for future studies involving the phase transfer catalyzed displacements. © 1996 John Wiley & Sons, Inc.     

Wanderung von SiAs im Temperaturgradienten ohne Zusatz eines Transportmittels – Experimente und Modellrechnungen

On the Migration of SiAs without using a Transport Agent – Experiments and Thermochemical Calculations SiAs migrates in a temperature gradient (T = 0.5 · (T₁ + T₂) = 850 to 1000°C) without adding a transport agent, into the cooler part of the silica ampoule. The migration rate depends on the temperature and the partial pressure of elemental arsenic in the silica tube. The migration rates were measured for various arsenic concentrations (0 ≤ n(As) ≤ 4 mmol/20 cm³) and for various mean transport temperatures (850 ≤ T le; 1000°C). In case of increasing the temperature the migration rate rises (e.g. T = 850°C, ?(exp.) = 0.006 mg/h; T = 1000°C, ?(exp.) = 0.044 mg/h). Adding arsenic (e.g. n(As) = 0.11 mmol, ?(exp.) = 0.067 mg/h; n(As) = 4.0 mmol, ?(exp.) = 0.82 mg/h), gives also the result of an increasing migration rate. Augmenting the pressure by adding argon as inert gas has only a small effect to the migration rate of SiAs. To explain the mechanism of the migration by using model calculations, the thermochemical data of the gaseous species SiAs_g and SiAs_{3, g} have to be estimated. According to model calculations an endothermic reaction like the following one is responsible for the migration of SiAs the region of the lower temperature: SiAs_s + 2 As_{n, g} = SiAs_{3, g} (1 ≤ n ≥ 4).     

An experimental and theoretical study of the product distribution of the reaction CH2 (X 3B1) + NO

Measurements of the product branching ratios of the reaction CH2 (X 3B1) + NO (1) are presented together with calculations of the thermal rate constant and branching ratios using unimolecular rate theory. The reaction was investigated experimentally at room temperature using FTIR spectroscopy. The yields of the main products HCNO and HCN were found to be gamma HCNO = 0.89 +/- 0.06, gamma HCN = 0.11 +/- 0.06. Other minor products could be rationalized by numerical simulations of the reaction system taking into account possible consecutive reactions. The potential energy surface for the reaction was characterized by quantum chemical calculations using ab initio and density functional methods. The proposed reaction pathways connecting reactants to products were explored by multi-channel unimolecular rate theory calculations to determine the CH2 (X) + NO capture rate constant and the rate constants for the different product channels as a function of temperature. The calculated capture rate constant of k = 2.3 x 10(13) cm3 mol-1 s-1 is in good agreement with experimental values at room temperature. Collisional stabilization of the initial H2CNO recombination complex was predicted to be negligible up to pressures of > 1 bar. For ambient pressures and temperatures up to 2000 K, HCNO + H were calculated as the dominating products, with gamma HCNO approximately 0.94 in agreement with the experiments. The channel to HCN + OH was calculated with 0.015 < or = gamma HCN < or = 0.05, only slightly below the experimental value.     

Ethylene oxidation under conditions of the oxidative coupling of methane

Ethylene conversion under conditions of the oxidative coupling of methane has been investigated. In an empty reactor above 740°C, ethylene oxidation occurs at a higher rate and its main product is carbon monoxide. Filling the reactor with an inert material (quartz) or a NaWMn/SiO₂ catalyst leads to a marked decrease in the ethylene conversion rate. Addition of methane to the reaction mixture dramatically slows down ethylene conversion rate and increases the C₃ hydrocarbon content of the reaction products. The kinetics of ethylene oxidation in the presence of methane over the NaWMn/SiO₂ catalyst is reported.     

Reactions of cobalt clusters with deuterium

The kinetics of chemical reactions of cobalt clusters Co_n with deuterium are described. Absolute rate constants have been measured in the size range n=7–68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by a factor of 400. This size dependence is most prominent for n=7 to 25: Co₁₅ is the most reactive cluster, and Co_7–9 and Co_19–20 are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n=25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.     

Ultracold collisions and reactions of vibrationally excited OH radicals with oxygen atoms

We report a quantum dynamics study of O + OH (v = 1, j = 0) collisions on its ground electronic state, employing two different potential energy surfaces: the DIMKP surface by Kendrick and Pack, and the XXZLG surface by Xu et al. A time-independent quantum mechanical method based on hyperspherical coordinates has been adopted for the dynamics calculations. Energy-dependent probabilities and rate coefficients are computed for the elastic, inelastic, and reactive channels over the collision energy range E(coll) = 10(-10)-0.35 eV, for J = 0 total angular momentum. Initial state-selected reaction rate coefficients are also calculated from the J = 0 reaction probabilities by applying a J-shifting approximation, for temperatures in the range T = 10(-6)-700 K. Our results show that the dynamics of the collisional process and its outcome are strongly influenced by long-range forces, and chemical reactivity is found to be sensitive to the choice of the potential energy surface. For O + OH (v = 1, j = 0) collisions at low temperatures, vibrational relaxation of OH competes with reactive scattering. Since long-range interactions can facilitate vibrational relaxation processes, we find that the DIMKP potential (which explicitly includes van der Waals dispersion terms) favours vibrational relaxation over chemical reaction at low temperatures. On the DIMKP potential in the ultracold regime, the reaction rate coefficient for O + OH (v = 1, j = 0) is found to be a factor of thirteen lower than that for O + OH (v = 0, j = 0). This significantly high reactivity of OH (v = 0, j = 0), compared to that of OH (v = 1, j = 0), is attributed to enhancement caused by the presence of a HO(2) quasibound state (scattering resonance) with energy near the O + OH (v = 0, j = 0) dissociation threshold. In contrast, the XXZLG potential does not contain explicit van der Waals terms, being just an extrapolation by a nearly constant function at large O-OH distances. Therefore, long-range potential couplings are absent in calculations using the XXZLG surface, which does not induce vibrational relaxation as efficiently as the DIMKP potential. The XXZLG potential leads to a slightly higher reactivity (a factor of 1.4 higher) for O + OH (v = 1, j = 0) compared to that for O + OH (v = 0, j = 0) at ultracold temperatures. Overall, both potential surfaces yield comparable values of reaction rate coefficients at low temperatures for the O + OH (v = 1, j = 0) reaction.     

Photochemical reactions of electron-deficient olefins with N,N,N′,N′-tetramethylbenzidine via photoinduced electron-transfer

Photoinduced electron transfer reactions of several electron-deficient olefins with N,N,N′,N′-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields ³TMB* after rapid intersystem crossing from ¹TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), -acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (π-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants have been also obtained by calculating with Stern–Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic k_q values for CN and CrN in endergonic region may be the disturbance of exciplexs formation.     

1H NMR analysis of the tolylene-2,4-diisocyanate – methanol reaction

<正>Tolylene-2,4-diisocyanate(2,4-TDI) 1 reacts with methanol through two simultaneous paths in the polyurethane reaction,which involve two different intermediates-tolylene-4-carbamatic-2-isocyanate 2 and tolylene-2-carbamatic-4-isocyanate 3,and the final product is tolylene-2,4-dicarbamate 4.The-CH_3 chemical shifts in benzene ring in compounds 1,2,3 and 4 can be easily tested and well distinguished,through which those four compounds are quantified and their kinetics are investigated.It shows that four rate constants for the tolylene-2,4-diisocyanate-methanol reaction in CCl_4 at 50℃are k_1=9.6×10~(-2)h~(-2)mol~(-2)min~(-1), k_2=1.4×10~(-2)h~(-2)mol~(-2)min~(-1),k_3=4.0×10~(-3)h~(-2)mol~(-2)min~(-1),k_4=1.4×10~(-3)h~(-2)mol~(-2)min~(-1).(k_1 is the reaction rate constant from compounds 1 to 2;k_2 is the reaction rate constant from compounds 1 to 3;k_3 is the reaction rate constant from compounds 3 to 4;k_4 is the reaction rate constant from compounds 2 to 4).     

A quasiclassical trajectory study of the reaction H + O2 <==> OH + O with the O2 reagent vibrationally excited

Quasiclassical trajectories have been computed on the Melius-Blint (MB) Potential Energy Surface (PES) and on the Double Many-Body Expansion (DMBE) IV PES of Pastrana et al. describing the H + O(2) <==> OH + O reaction with the nonrotating (J = 0) O(2) reagent vibrationally excited to levels v = 6, 7, 8, 9, and 10 at four temperatures: 1000, 2000, 3000, and 4000 K. The vibrational energy levels were selected by using a semiclassical Einstein-Brillouin-Keller (EBK) quantization procedure while the relative translational energy was sampled from a Boltzmann weighted distribution. The rate coefficient for the formation of the OH + O products is seen to increase monotonically with quantum number and nearly monotonically with temperature. On the MB PES, at T = 1000 K, the total rate coefficient increases by a factor of 5.2 as the initial vibrational quantum number of the O(2) diatom increases from v = 6 to v = 10. For T = 2000 K, this factor drops to 3.3, to 2.9 for T = 3000 K, and to 2.5 for T = 4000 K. On the DMBE IV PES, at T = 1000 K the total rate coefficient increases by a factor of 4.1 as the initial vibrational quantum number of the O(2) diatom increases from v = 6 to v = 10. For T = 2000 K, this factor drops to 3.5, to 2.1 for T = 3000 K, and to 2.0 for T = 4000 K. The less-direct group (defined below) of trajectories is sensitive to the initial O(2) vibrational excitation in several different temperature ranges, apparently retaining the effect of reagent vibrational excitation. The more-direct group (defined below) of trajectories does not exhibit this behavior. Reagent vibrational excitation does not increase the total rate coefficients for the title reaction more than the increase due to a simple temperature increase. The less-direct and more-direct groups of trajectories differ in their contribution to the rate coefficient for the title reaction. In particular, at T = 4000 K, the two PESs used in this work differ dramatically in the roles of the less-direct and more-direct trajectories. The behavior of the more-direct and less-direct groups of trajectories can be understood in terms of the efficiency of intramolecular vibrational energy transfer. This work utilizes the recently introduced PES Library, POTLIB 2001, which made the comparisons between the two PESs discussed in this work possible in a very straightforward way.     

利用E-V传能模型研究亚稳态分子PCl(b^1∑^+)的猝灭过程

亚稳态分子猝灭机理的研究一直受到人们的极大重视。本文利用E-V传能模型对亚稳态分子PCl(b^1∑^+)的猝灭过程进行了定量处理。结果表明PCl(b^1∑^+)的猝灭是PCl(b^1∑^+→a^1Δ)跃迁和试剂分子端键X-Y振动能级近共振传能的结果, 与PCl(b^1∑^+→a^1Δ)跃迁的Franck-Condon因子及试剂分子端键X-Y振动的非谐性系数有关, 而且也受猝灭试剂分子极化率的影响。     

Ruthenium bisbipyridine complexes of horse heart cytochrome c: characterization and comparative intramolecular electron-transfer rates determined by pulse radiolysis and flash photolysis

The reaction of [Ru(bpy)2L(H2O)]2+ (bpy = 2,2'-bipyridine, L = imidazole, water) with reduced horse heart cytochrome c results in coordination of [RuII(bpy)2L] at the His 33 and His 26 sites. Coordination at the His 33 site gave a diastereomeric [RuII(bpy)2L]-His-cyt c(II) mixture favoring the lambda-Ru form regardless of the substituent on the bipyridine ligands, while substitution at the more buried His 26 site gave an isomeric distribution that varies according to the substituent on the bipyridine ligands. The diastereomeric aquoproteins (L = H2O) are distinguished by their redox potentials and their conversion to the corresponding fluorescent imidazole proteins. Intramolecular electron transfer between the reduced ruthenium bipyridine and cyt c(III) in [RuII(bpy.)(bpy)L]-His33-cyt c(III) was determined by reductive pulse radiolysis using the aqueous electron as a reducing agent, kret = (2.0 +/- 0.3) x 10(5) s-1, and kret is independent of the sixth ligand L = H2O, imidazole. In addition, the rate constant for intramolecular electron transfer from cyt c(II) to the ruthenium(III) center in [RuIII(bpy)2L]-His33-cyt c(II) was determined by oxidative pulse radiolysis using azide and carbonate radicals. This rate is very sensitive to the nature of the sixth ligand. When L = H2O, the intramolecular electron-transfer rate for the major diastereomer lambda-cis-[RuIII (bpy)2(H2O)]-His33-cyt c(II) is k = 1.1 x 10(4) s-1 and is independent of pH between 5.6 and 8.3. The minor delta-cis-[RuIII(bpy)2(H2O)]-His33-cyt c(II) isomer has pH-dependent electrochemistry and a lower rate of intramolecular electron transfer. Complete conversion from L = H2O to L = imidazole is slow, requiring more than 7 days in 1 M imidazole. A lower limit (k > 2 x 10(6) s-1) for the intramolecular electron-transfer rate constant in [RuIII(bpy)2(L)]-His33-cyt c(II), L = imidazole, could be obtained by pulse radiolysis in the absence of the slower reacting aquo species. This observation is in agreement with the value of 3 x 10(6) s-1 measured by flash photolysis. Earlier pulse radiolysis experiments primarily measured the aquoligated ruthenium protein, while the flash photolysis experiments measured the imidazole-ligated fraction because it is the only species oxidatively quenched in the photoinduced reactions. Intramolecular electron-transfer reactions for a new series of ruthenium bipyridine complexes, [Ru(dabpy)2L]-His33-cyt c proteins (dabpy = 4,4'-diamino-2,2'-bipyridine) (L = imidazole, pyridine, isonicotinamide and pyrazine), proceed with lower driving force, resulting in slower rate constants amenable to measurement by oxidative pulse radiolysis. The electron-transfer rate constants for this series spanned a wide range of the Marcus log k vs delta G plot.     

A classical trajectory study of the effect of reaction barrier height on the vibrational energy transfer efficiency in the Cl + HCl system

The effects of reaction barrier height and initial rotational excitation of the reactants on the overall rate of H atom exchange between atomic chlorine and HCl (v = 0) and on the 0 → 1 vibrational excitation of HCl via reactive and nonreactive collisions have been investigated using quasiclassical trajectory techniques. Two empirical LEPS potential energy surfaces were employed in the calculations having reaction barrier heights of 9.84 and 7.05 kcal mol^?1. Trajectory studies of planar collisions were carried out on each surface over a range of relative translational energies with the ground-state HCI collision partner given initial rotational excitation corresponding J = 0, 3, and 7. Initial molecular rotation was found to be relatively inefficient in promoting the H atom exchange; the computed rate coefficient for H atom exchange between Cl + HCl (v = 0, J = 7) was only 4 times larger than that for CI + HCI (v = 0, J = 0). The vibrational excitation rate coefficient exhibited a stronger dependence on initial molecular rotational excitation. The observed increase in the vibrational excitation rate coefficient with increasing initial molecular rotational excitation was due primarily to nonreactive intermolecular R → V energy transfer. The vibrational excitation rate coefficients increase with decreasing reaction barrier height.