Contribution of water dimer absorption to the millimeter and far infrared atmospheric water continuum

We present a rigorous calculation of the contribution of water dimers to the absorption coefficient alpha(nu,T) in the millimeter and far infrared domains, over a wide range (276-310 K) of temperatures. This calculation relies on the explicit consideration of all possible transitions within the entire rovibrational bound state manifold of the dimer. The water dimer is described by the flexible 12-dimensional potential energy surface previously fitted to far IR transitions [C. Leforestier et al., J. Chem. Phys. 117, 8710 (2002)], and which was recently further validated by the good agreement obtained for the calculated equilibrium constant Kp(T) with experimental data [Y. Scribano et al., J. Phys. Chem. A. 110, 5411 (2006)]. Transition dipole matrix elements were computed between all rovibrational states up to an excitation energy of 750 cm(-1), and J=K=5 rotational quantum numbers. It was shown by explicit calculations that these matrix elements could be extrapolated to much higher J values (J=30). Transitions to vibrational states located higher in energy were obtained from interpolation of computed matrix elements between a set of initial states spanning the 0-750 cm(-1) range and all vibrational states up to the dissociation limit (approximately 1200 cm(-1)). We compare our calculations with available experimental measurements of the water continuum absorption in the considered range. It appears that water dimers account for an important fraction of the observed continuum absorption in the millimeter region (0-10 cm(-1)). As frequency increases, their relative contribution decreases, becoming small (approximately 3%) at the highest frequency considered nu=944 cm(-1).     

水蒸气对高岭土高温吸附铅的影响

使用沉降炉开展了水蒸气对高岭土高温吸附铅影响的实验研究，其中铅的形态为PbO和PbCl₂两种。首先研究了0-20%水蒸气对高岭土吸附PbO（1100-1300 ℃）和PbCl₂（800-1300 ℃）的影响规律，然后基于XRD、SEM和残余羟基率等分析，掌握了水蒸气影响高岭土高温吸附的机理。结果表明，水蒸气可以减少高岭土表面羟基的高温脱落，从而阻碍了PbO吸附、促进了PbCl₂吸附。综合高温下惰性莫来石的出现和高岭土孔隙结构的坍塌等因素，PbO和PbCl₂的最佳吸附温度分别为1200和1000 ℃。     

Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.     

Differential permeation and absorption of water vapor in polyacrylamide film

An investigation has been made of successive differential absorption and differential permeation of water vapor in polyacrylamide a t 30°C. The successive differential ab sorptions showed two types of non-Fickian anomalies: sigmoid type and two-stage type curves. The experimental data have been analyzed in terms of the Fick diffusion equation assuming a time-dependent approach of the surface concentration. The calculated family of absorption curves agreed with the experimental results. The permeation curves in the region of high and low pressure increments were apparently normal, but at medium pressures they showed anomalous behavior. It was found that in the differential type of permeation experiment the stress effect induced by a concentration gradient between the surfaces of the film was eliminated. By assuming the time-dependent approach of the equilibrium surface concentration, we calculated the time lag as a function of film thickness and applied the theory to the data for permeation through polyacrylamide film with different film thicknesses a t relatively small pressure intervals. The rate parameter calculated from permeation data was found to be in good agreement with that from successive differential absorption data.     

An ab initio calculation of the absorption cross section of water in the first absorption continuum

We present a complete ab initio study of the photodissociation of water in the first absorption band including a calculated excited-state potential and a calculated transition dipole function. The dynamical treatment is based on the IOS approximation for the rotational degree of freedom. The vibrationally coupled equations are solved exactly using polar coordinates. Agreement with the experimental absorption spectrum is excellent and even the “vibrational” structures are reproduced. A dynamical interpretation of these structures in terms of features of the à ¹B₁ surface is given.     

CO_2 absorption with ionic liquids at elevated temperatures

CO_2 capture with ionic liquids(ILs) has attracted many attentions, and most works focused on absorption ability at ambient temperatures, while seldom research was concerned at elevated temperatures.This not only limits the CO_2 absorption application at elevated temperature, but also the determination of the operation condition of the CO_2 desorption generally occurring at higher temperature. This work mainly reported CO_2 solubilities in ILs at elevated temperatures and related properties were also provided. 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([CnMIm][Tf_2N]) ILs were selected as physical absorbents for CO_2 capture in this work due to their relative higher CO_2 absorption capacities and good thermal stabilities. The long-term stability tests showed that [CnMIm][Tf_2N] is thermally stable at 393.15 K for long time. CO_2 solubilities in [CnMIm][Tf_2N] were systematically determined at temperatures from 353.15 K to 393.15 K. It demonstrated that CO_2 solubility obviously increases with the increase of pressure while slightly decreases with increase of temperature. As the length of alkyl chain on the cation increases, CO_2 solubility in ILs increases. Additionally, the thermodynamic properties including the Gibbs free energy, enthalpy, and entropy of CO_2 were also calculated.     

Infrared and Raman spectra of crystalline para-bromoaniline at low temperatures

The polarization characteristics of the i.r. absorption bands of oriented p-bromoaniline crystal films have been studied at low temperatures. Raman spectra of this compound in solution and in the polycrystalline state have been recorded as an aid to the vibrational assignment of the crystal bands. The vibrational spectra are interpreted to deduce the crystal factor group (D_2h) and the molecular site symmetry (C_s). The observed factor group splittings and dichroic ratios suggest the crystal unit cell of p-bromoaniline to be isostructural with that of p-chloroaniline.     

Simulations of vapor water clusters at vapor-liquid equilibrium

The Gibbs-ensemble Monte Carlo methods based on the extended single point charge [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. 91, 6269 (1987)] potential-energy surface have been used to study the clustering of vapor phase water under vapor-liquid equilibrium conditions between 300 and 600 K. It is seen that the number of clusters, as well as the cluster size, increase with temperature. This is primarily due to the increase in vapor density that accompanies the temperature increase at equilibrium. In addition, due to entropic effects, the percentage of clusters that have linear (or open) topologies increases with temperature and dominates over the minimum-energy cyclic topologies at the temperatures studied here. These results are insensitive to the number of molecules used in the simulations and the criterion used to define a water cluster.     

Adsorption tests of water vapor on synthetic zeolites for an atmospheric detritiation dryer

Tritiated hydrogen and hydrocarbon are usually oxidized to a tritiated water vapor to make the tritium adsorbable and easy to treat. The adsorption system as a subsequent process plays an important role in a tritium recovery and its performance affects the overall detritiation efficiency significantly. In order to quantify an adsorbent's utilization and its dynamic capacity against an inlet humidity and a flow rate, a series of quantitative tests based on the breakthrough behavior were carried out in an isothermal fixed bed of synthetic zeolites such as molecular sieve 4A, 5A, 13X and mordenite. The amount of water vapor breaking during the adsorption was estimated to provide a breakthrough capacity at the various inlet flow rates and humidity conditions. The molecular sieve 13X exhibited a better adsorption performance at a given bed height. The existence of CO₂ in a humid atmosphere had a minor effect on the net adsorption capacity and the hydrogen isotopic water (HDO) in the elution stream showed a delayed behavior during a thermal desorption.     

Infrared spectra of ammonium nitrate at high pressures and low temperatures

Infrared spectra showing the symmetric stretching vibration band, γ₁, of the nitrate ion (rendered weakly infrared active by the crystal field) were recorded for sample pressures up to 6 k bar at temperatures ranging between room temperature and liquid nitrogen temperature. A pressure-temperature phase diagram for the λ-transition of ammonium nitrate has been obtained. The spectra at low temperatures and low pressures are shown to be due to mixtures of phase IV and phase VII and the importance of long-range as well as short-range order is considered.     

Fast-neutron radiolysis of acid water at elevated temperatures

Determination of G-values of water decomposition products in acid formed by irradiation of fast neutrons from a reactor YAYOI at elevated temperatures up to 275°C was carried out with a combination of an aerated and a deaerated Fricke dosimeters and a cerium dosimeter. As a first step, the dosimetry of the radiation field revealed that the average energy of the fast neutrons is 0.8 MeV, and over 90% of the total dose absorbed by the aqueous solutions comes from fast neutrons. At room temperature, G-values evaluated for water decomposition products, G_H + Ge^-_aq = 1.25, G_OH = 0.68, G_H2 = 0.99, G_H2O2 = 1.27 and G_-H2O = 3.21, coincide with those at initial LET of about 4 eV/Å. With increasing temperature, radical products increase and molecular products decrease, and above 150°C, relative G-values of the products seem to be similar to those obtained in γ-radiolysis at room temperature; however, G_-H2O decreases slightly. On the basis of the above results, the temperature effect of water decomposition with fast neutron at elevated temperatures is concluded to be very different from that by γ-rays, where no drastic change in the decomposition pattern with temperature was found.     

Infrared spectrum and absorption coefficient of the cofactor flavin in water

Flavins play a key role as redox cofactors of enzymes involved in important metabolic processes. Moreover, they undergo photochemical reactions as chromophores in sensors of blue light or magnetic field in many organisms. The reaction mechanisms of flavoproteins have been investigated by infrared spectroscopy and theoretical studies. However, basic information on flavins in the infrared spectral range has been missing, such as absorption spectra in water and absorption coefficients. Here, the cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) were investigated in aqueous medium by Fourier transform infrared spectroscopy. Transmission and attenuated total reflection (ATR) configuration were employed in direct comparison. Absorption spectra in the range of 920–1800 cm⁻¹ were determined after accurate subtraction of the contributions from the water vibrations. The important carbonyl vibrations were resolved at 1661 and 1712 cm⁻¹. The absorption spectra may serve as a reference for theoretical and experimental studies on the effect of the microenvironment on the flavin cofactor. Furthermore, the molar absorption coefficient of FAD at 1547 cm⁻¹ was determined to 2200 L mol⁻¹ cm⁻¹ with an integral absorption coefficient of ∼50,000 L mol⁻¹ cm⁻². These values are prerequisite for the determination of reaction yields in flavoproteins from reaction-induced difference spectra.     

常压气相氧化羰基化合成碳酸二乙酯

碳酸二乙酯是一种重要的有机化工原料,可广泛用于合成农药如脱叶灵,医药如喹啉酮衍生物,中间体3-氧硫代羧酸酯,还可用于电子管阴极的镀层[1-3]。生产碳酸二乙酯的传统方法为:无水乙醇与光气反应生成氯甲酸乙酯,氯甲酸乙酯继续与乙醇反应生成碳酸二乙酯后经水洗蒸馏制成。使用光气为原料对设备的要求较高。我们在常压下气相羰基化合成碳酸二乙酯[4]:2ＮＯ+Ｃ2Ｈ5ＯＨ+0.5Ｏ2→2Ｃ2Ｈ5ＯＮＯ+Ｈ2Ｏ(1)ＣＯ+2Ｃ2Ｈ5ＯＮＯ→(Ｃ2Ｈ5Ｏ)2ＣＯ+2ＮＯ(2)产生的一氧化氮可与氧气和乙醇进行反应再生为亚硝酸乙酯,符合原子经济反应且几乎不放出对…     

Some consequences of high temperature water vapor spectroscopy: water dimer at equilibrium

It is shown that the evolution of water vapor spectra in the 2500-5000 cm(-1) range recorded at 650 K and pressures up to 130 atms after subtraction of monomer contribution may be interpreted qualitatively well on the basis of experimental data on water dimer and trimer obtained from cold molecular beams and in He droplets. The proposed spectroscopic model considers water vapor as a mixture of nonideal monomers, dimers, and trimers at chemical equilibrium. The effect of line mixing is taken into account in the monomer spectrum modeling. Decomposition of the high temperature spectra allowed determining a dimer equilibrium constant that was compared with the previously known values. The contribution of water trimer is assessed. The performed analysis indicates that the number of bound dimers in water vapor is quite large, even at such a high temperature.     

Liquid water confined in carbon nanochannels at high temperatures

Structure, hydrogen bonding, electrostatics, dielectric, and dynamical properties of liquid water confined in flat graphene nanochannels are investigated by molecular dynamics simulations. A wide range of temperatures (between 20 and 360 degrees C) have been considered. Molecular structure suffers substantial changes when the system is heated, with a significant loss of structure and hydrogen bonding. In such case, the interface between adsorbed and bulk-like water has a marked tendency to disappear, and the two preferential orientations of water nearby the graphite layers at room temperature are essentially merging above the boiling point. The general trend for the static dielectric constant is its reduction at high temperature states, as compared to ambient conditions. Similarly, residence times of water molecules in adsorbed and bulk-like regions are significantly influenced by temperature, as well. Finally, we observed relevant changes in water diffusion and spectroscopy along the range of temperatures analyzed.     

Investigating the adhesion of water droplets at low temperatures

Adhesion of droplets to solid surfaces at low temperatures is crucial for antifogging and antifreezing, etc. So far, most reports on adhesion measurements have been carried out in air-liquid-solid systems, but it remains difficult to precisely investigate the adhesion at low temperatures due to the uncontrollable condensation. On the basis of the liquid-liquid-solid system, a new method to measure the adhesion of water droplets at low temperatures was developed and employed. Moreover, the reported method could be viable in other liquid-liquid-solid systems with wider temperature window; thus, it will find applications in broad fields such as crude oil recovery, ore-dressing, and transfer printing.