Water vapour self-continuum and water dimers: 1. Analysis of recent work

Recent laboratory observations and advances in theoretical quantum chemistry allow a reappraisal of the fundamental mechanisms that determine the water vapour self-continuum absorption throughout the infrared and millimetre wave spectral regions. By starting from a framework that partitions bimolecular interactions between water molecules into free-pair states, true bound and quasi-bound dimers, we present a critical review of recent observations, continuum models and theoretical predictions. In the near-infrared bands of the water monomer, we propose that spectral features in recent laboratory-derived self-continuum can be well explained as being due to a combination of true bound and quasi-bound dimers, when the spectrum of quasi-bound dimers is approximated as being double the broadened spectrum of the water monomer. Such a representation can explain both the wavenumber variation and the temperature dependence. Recent observations of the self-continuum absorption in the windows between these near-infrared bands indicate that widely used continuum models can underestimate the true strength by around an order of magnitude. An existing far-wing model does not appear able to explain the discrepancy, and although a dimer explanation is possible, currently available observations do not allow a compelling case to be made. In the 8-12 μm window, recent observations indicate that the modern continuum models either do not properly represent the temperature dependence, the wavelength variation, or both. The temperature dependence is suggestive of a transition from the dominance of true bound dimers at lower temperatures to quasi-bound dimers at higher temperatures. In the mid- and far-infrared spectral region, recent theoretical calculations indicate that true bound dimers may explain at least between 20% and 40% of the observed self-continuum. The possibility that quasi-bound dimers could cause an additional contribution of the same size is discussed. Most recent theoretical considerations agree that water dimers are likely to be the dominant contributor to the self-continuum in the mm-wave spectral range.     

First CRDS-measurements of water vapour continuum in the 940 nm absorption band

Measurements of near-infrared water vapour continuum using continuous wave cavity ring down spectroscopy (cw-CRDS) have been performed at around 10611.6 and . The continuum absorption coefficients for N₂-broadening have been determined to be and at , and and at , respectively.These results represent the first near-IR continuum laboratory data determined within the complex spectral environment in the 940 nm water vapour band and are in reasonable agreement with simulations using the semiempirical CKD formulation.     

IR absorption spectrum (4200–3100 cm) of H2O and (H2O)2 in CCl4. Estimates of the equilibrium constant and evidence that the atmospheric water absorption continuum is due to the water dimer

IR absorption spectra, 4200–3100 cm⁻¹, of water in CCl₄ solutions are presented. It is shown that for saturated solutions significant amounts of water are present as dimer (ca. 2%). The IR spectra of the monomer and dimer are retrieved. The integrated absorption coefficients of the monomer absorption are significantly enhanced relative to the gas phase values. The dimer spectrum consists of 5 bands, of which 4 were expected from data from cold beams and cold matrices. The origin of the “extra” band is discussed. In addition it is argued that the dimer absorption bands intensities must be enhanced relative to the gas phase values. Based on recent calculations of band strengths, and observed frequency shifts relative to the gas phase, the intensity enhancement factors are estimated as well as the monomer/dimer equilibrium constant in CCl₄ solution at T=296 K (K_c=1.29 mol⁻¹ L). It is noted that the observed dimer spectrum has a striking resemblance with the water vapour continuum determined by Burch in 1985 which was recently remeasured by Paynter et al. and it is concluded that the atmospheric water absorption continuum in the investigated spectral region must be due to water dimer. Based on the newly published spectral data a revised value of the gas phase equilibrium constant is suggested (K_p=0.035 atm⁻¹ at T=296 K) as well as a value for the standard enthalpy of formation, ΔH⁰=15.4 kJ mol⁻¹.     

Evaluation of suitable spectral intervals for near-IR laboratory detection of water vapour continuum absorption

The water vapour continuum absorption is an important component of molecular absorption of radiation in atmosphere. However, uncertainty in knowledge of the value of the continuum absorption at present can achieve 100% in different spectral regions leading to an error in flux calculation up to 3-5 W/m² global mean. This work uses line-by-line calculations to reveal the best spectral intervals for experimental verification of the CKD water vapour continuum models in the currently least-studied near-infrared spectral region. Possible sources of errors in continuum retrieval taken into account in the simulation include the sensitivity of laboratory spectrometers and uncertainties in the spectral line parameters in HITRAN-2004 and Schwenke-Partridge database. It is shown that a number of micro-windows in near-IR can be used at present for laboratory detection of the water vapour continuum with estimated accuracy from 30% to 5%.     

Evidence for the electron-electron scattering contribution to the electrical resistivity of aluminum

It is demonstrated that the recent low-temperature electrical resistivity data for aluminum provide experimental evidence for the presence of a T² contribution to the electrical resistivity due to electron-electron scattering.     

水蒸气对声致发光单气泡稳定性的影响

在考虑水蒸气凝结与水的蒸发过程的基础上，推导了球形气泡形状稳定性方程-利用这个方程以及气泡运动时的气体扩散平衡条件，分别研究了环境水温217℃时声驱动频率为206kHz（溶于水中的氩气含量是其饱和度的14％）、环境水温0℃时声驱动频率为319kHz（溶于水中的氮气分压为20kPa，其中含1％氩气），以及环境水温20℃时声驱动频率为338kHz（溶于水中的氮气分压为20kPa，其中含1％氩气）可控制条件下气泡稳定性问题-理论计算结果与前人的实验数据比较，发现考虑水蒸气以后比忽略水蒸气对单气泡稳定区域 关键词： 声致发光 水蒸气 形状不稳定性 扩散平衡     

A generic model for the ionic contribution to the equation of state

Abstract

We describe an extended standard model that yields the thermodynamics of the ionic contribution for general materials, from the low temperature solid region, through melting, to the ideal gas limit. We use the Debye model for the solid. Melting is determined by the Lindemann formula with standard rules of thumb used to determine density and energy discontinuities. The model interpolates through the liquid regime to the ideal gas assuming that the specific heat drops monotonically from about 3R at melting, to 9R/4 at five times melting, and continuing to 3R/2 at high temperatures. The area under the specific heat curve is constrained in the model to reproduce the correct high temperature entropy. Thus, for a compound the extra contribution from the entropy of mixing forces into the model, in a crude way, the extra specific heat due to dissociation.     

A reaction kinetics model of water sonolysis in the presence of a spin-trap

The time development of the concentration of a spin-trapped OH radical was studied by electron spin resonance at various sound intensities and various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations in water sonolysis. The lifetime of the spin-trapped OH radical was also studied, and factors governing sonolysis are discussed. We found that the production of spin-trapped OH radical increases with increasing ultrasound intensity. The lifetime of a spin-trapped OH radical decreases linearly with increase in sonication time. This result suggests that an unknown scavenger is produced by ultrasound. Based on the above results, we suggested a model of the reaction kinetics and estimated the production rate of OH radical from this model.     

Use of Euler series to fit spectra with application to water

Power series expansions of water eigenstate energies in J and K converge poorly and show alternating signs of the coefficients of the power series. Euler series can be used effectively to change an alternating series into one where all the coefficients have the same sign and where the radius of convergence is increased. This paper extends the Euler series to a two-dimensional series in K² and [J (J + 1) − K²]. Application of this Euler series to the rotational energies of the ground state and the first 4 excited vibrational states of water allows a fit to experimental accuracy to J = 22 and K = 22. This fit has good convergence and also has predictive capability. It is much easier to fit the perturbed states because the Euler series allows the zero-order energy the perturbed states to be predicted with more confidence.     

Evidence of the photonic gap contribution to the guiding mechanism for strongly confined modes in the refractivelike domain

The group index dispersion and birefringence of guided modes supported by straight photonic crystal (PhC) waveguides are theoretically and experimentally investigated as a function of the waveguide width within various reduced frequency domains. Within the photonic gap and far from the Brillouin zone edges, strongly confined modes supported by narrow PhC guides exhibit both a group index and a birefringence larger than those of a deep ridge. These two results evidence the contribution of the photonic gap to the guiding mechanism in the refractivelike domain.     

Adsorption of NO on Au atoms and dimers supported on MgO(1 0 0): DFT studies

The adsorption of NO on single gold atoms and Au₂ dimers deposited on regular O²⁻ sites and neutral oxygen vacancies (F_s sites) of the MgO(1 0 0) surface have been studied by means of DFT calculations. For Au₁/MgO the adsorption of NO is stronger when the Au atom is supported on an anionic site than when it is on a F_s site, with adsorption binding energies of 1.1 and 0.5 eV, respectively. In the first case the spin density is mainly concentrated on the metal atom and protruding from the surface. In such a way, an active site against radicals such as NO is generated. On the F_s site, the presence of the vacancy delocalizes the spin into the substrate, weakening its coupling with NO. For Au₂/MgO, as this system has a closed-shell configuration, the NO molecules bonds weakly with Au₂. Regarding the N–O stretching frequencies, a very strong shift of 340–400 cm⁻¹ to lower frequencies is observed for Au₁/MgO in comparison with free NO.     

Bound water: Evidence from and implications for the dielectric properties of aqueous solutions

Broadband dielectric spectra of a variety of aqueous solutions are evaluated as to indications of water that may be considered bound. Static permittivity decrements due to depolarizing internal electric fields, from kinetic depolarization, as well as from dielectric saturation are discussed. The latter effect reflects the preferential orientation of water permanent dipole orientations within strong Coulombic field of small ions, especially multivalent cations. Such water may be considered bound even though rapid rotations around the orientation of the electric dipole moment are definitely possible and also a fast exchange of water molecules between the hydration region and the bulk may take place. Water exhibiting large dielectric relaxation times, as typical for regions with large local concentration of foreign matter, may also be named bound. However, no clear evidence for interaction energies exceeding the hydrogen bond energy of pure water has been found. Rather enhanced relaxation times at low water content reflect the small concentration of hydrogen bonding sites and thus low probability density for the formation of a new hydrogen bond. Potential interferences of the water relaxation with relaxations from other molecules or from ionic structures are mentioned briefly.     

Effect of water vapour on particulate matter emission during oxyfuel combustion of char and in situ volatiles generated from rapid pyrolysis of chromated-copper-arsenate-treated wood

This paper reports the effect of water vapour on particulate matter (PM) during the separate combustion of in situ volatiles and char generated from chromated-copper-arsenate-treated (CCAT) wood at 1300 °C. Combustion of in situ volatiles produces only PM with aerodynamic diameter?<1?µm (i.e., PM₁), dominantly PM with aerodynamic diameter?<0.1?µm (i.e., PM_0.1). Water vapour could significantly enhance the nucleation, coagulation and condensation of fine particles and reduce the capture of Na and K by the alumina reactor tube via reduced formation of alkali aluminates, leading to increases in both yield and modal diameter of PM_0.1. Water vapour could also enhance char fragmentation hence increase the yield of PM with aerodynamic diameter between 1 and 10?µm (i.e., PM_1–10) during char combustion. For trace elements, during in situ volatiles combustion, volatile elements (As, Cr, Ni, Cu and Pb) are only presented in PM₁ and water vapour alters the particle size distributions (PSDs) but has little effect on the yields of these trace elements. During char combustion, As, Cr, Cu and Ni are present in both PM₁ and PM_1–10 while the non-volatile Mn and Ti are only present in PM_1–10. Increasing water vapour content increases the yields of As, Cr, Cu, Ni, Mn and Ti in PM_1-10 due to enhanced char fragmentation. During char combustion, water vapour also originates less oxidising conditions locally for enhancing As release, promotes the generation of gaseous chromium oxyhydroxides and inhabits the production of NiCl₂ (g), leading to increased yields of As and Cr and decreased yield of Ni in PM_0.1.     

An integral model for simulating the environmental effects of water vapour releases from cooling towers

Summary This study presents an integral model for the simulation of the environmental effects produced by wet plumes released by cooling towers associated to large power plants. The environmental impact is evaluated in terms of the increase in the relative humidity at ground level and of the reduction of solar radiation due to the shade projected onto the ground by the visible plume. The paper discusses the parametrization of the model and its application to simulate the consequences of the introduction of a cooling tower in an area characterized by a regime of weak winds. Results are presented in terms of statistics of the plume behaviour over a period of four years. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, Rome, June 19–22, 1984.     

Contribution of H-bond vibrations to heat capacity of water

The origin of the anomalously large value of the heat capacity of liquid water is discussed. Comparing the temperature dependence of the heat capacities for water with those for argon and hydrogen sulfide, we separate contributions of the translational and rotational degrees of freedom. The residual part is considered as being caused by the specific contributions of the transversal vibrations of H-bonds. The estimate for the number of H-bonds per molecule is obtained from the analysis of this contribution. This estimate is in quite good agreement with the estimates which follow from the analysis of the specific volume, heat of evaporation, and kinematic shear viscosity.     

金等离子体中Au48+—Au52+平衡分布的统计热力学研究

基于全相对论多组态Dirac-Fock理论，采用“多功能相对论原子结构程序(GRASP2)”，考虑量子电动力学(QED)效应和Breit修正，涉及实验谱中Au等离子体M带的几类重要跃迁，计算了Au48+—Au52+离子的能级结构和能级简并度.用统计热力学方法计算 各离子的配分函数，由配分函数计算等离子体内这五种离子的电离与复合平衡常数，根据同 时反应的平衡理论研究电离与复合达到平衡时等离子体内各离子的相对分布. 关键词： 金等离子体 配分函数 平衡常数 离子丰度     

A viscous continuum traffic flow model with consideration of the coupling effect for two-lane freeways

In this paper, the viscous continuum traffic flow model for a single lane is extended to the traffic flow for two-lane freeways. The proposed model is a higher-order continuum model considering the coupling and lane changing effects of the vehicles on two adjacent lanes. It results from integrating the Taylor series expansion of the viscous continuum traffic flow model proposed by Ge (2006 Physica A 371 667) into the multi-lane model presented by Daganzo (1997 Transpn. Res. B 31 83). Our proposed model may be used to describe non-anisotropic behaviour because of lane changing in multi-lane traffic. A linear stability analysis is given and the neutral stability condition is obtained. Also, issues related to lane changing, shock waves and rarefaction waves, local clustering and phase transition are investigated through a simulation experiment. The simulation results show that the proposed model is capable of explaining some particular traffic phenomena commonly observable in real world traffic flow.     

半导体量子点形成临界尺寸的定量预测

半导体量子点是一类具有显著量子效应的零维量子结构,自组的模型系统,表现为Stranski-Krastanov型生长.其特征为,当超过3—4个Ge单原子层（浸润层）时,则由二维层状生长转变为三维岛状生长.Ge/Si量子点是初期形成的与衬底共格无位错的三维岛,岛表面由{105}晶面组成.文章作者利用第一性原理计算和介观理论模拟相结合的连续式多尺度（sequential multi-scale）方法,第一次对纯Ge和GeSi合金量子点在Si(001)表面的成核临界尺寸进行了定量的理论预测,同时研究了岛边缘的应力不连续对量子点稳定性的影响,实现了对Ge/Si量子点的形成和稳定性定量的理论研究.     

半导体量子点形成临界尺寸的定量预测

半导体量子点是一类具有显著量子效应的零维量子结构,自组的模型系统,表现为Stranski-Krastanov型生长.其特征为,当超过3-4个Ge单原子层（浸润层）时,则由二维层状生长转变为三维岛状生长.Ge/Si量子点是初期形成的与衬底共格无位错的三维岛,岛表面由{105}晶面组成.文章作者利用第一性原理计算和介观理论模拟相结合的连续式多尺度（sequential multi-scale）方法,第一次对纯Ge和GeSi合金量子点在Si（001）表面的成核临界尺寸进行了定量的理论预测,同时研究了岛边缘的应力不连续对量子点稳定性的影响,实现了对Ge/Si量子点的形成和稳定性定量的理论研究。