Multiple-electron excitation in X-ray absorption: a simple generic model

The probability of multiple-electron excitation in X-ray absorption is calculated using a simple generic model. The model permits calculations to be made for all atoms with little input data or computing effort. The high-energy limit of this probability, which gives the usual EXAFS amplitude reduction factor, is calculated in the 'sudden approximation' using Slater orbitals. Good agreement with experiment is found. The energy dependence of this probability is also calculated using a simple model form of perturbing potential and found to agree well with experiment for rare gas atoms. The effect on the X-ray absorption coefficient of including multiple-electron excitations is also determined and is found to be small, again in agreement with observation.     

逐线积分气体吸收模型及其在NDIR气体检测中的应用

介绍了一种精确的逐线积分痕量气体吸收模型,模型适用于中红外波段大气环境中痕量气体、污染气体检测的理论研究和工程应用。首先介绍了气体辐射特性的理论计算方法和现有逐线积分大气模 型,比较了各自的优劣性,其次详述了逐线积分计算的理论: 吸收系数是温度、波长、气体浓度和相关吸收线参数的函数,单条谱线的平均吸收系数是积分线强与谱线线型的卷积,在不同的大气条件下选 择不同的线型。最后,详细描述了模型的算法细节,并给出了模型计算的结果与傅里叶变换光谱仪实测数据的对比,举例介绍了吸收模型在NDIR气体探测技术中的实际应用,并使用该模型模拟了NDIR探 测器两个通道的信号强度随尾气中CO₂,CO浓度变化的关系,通过计算确定了NDIR探测器合适的工作范围。所述模型利用HITRAN光谱数据库,考虑了展宽、线翼截断、温度修正、光谱分辨 率变化等情况,可以有效的模拟大气环境中多种气体的红外吸收特征。     

The SLW-1 model for efficient prediction of radiative transfer in high temperature gases

A reduced SLW model consisting of a single gray gas and a clear gas is developed as an efficient spectral method for modeling radiation transfer in high temperature gases. It is shown that the SLW-1 model is not simply a reduction of the SLW method to the case of a single gray gas. Good accuracy can be achieved by the optimal choice of the model’s gray gas absorption coefficient and its weight by application of the Absorption-Line Blackbody Distribution Function (ALBDF), which is calculated with a high-resolution spectral database. Different approaches to the construction of the SLW-1 model are shown. The SLW-1 model absorption spectrum still has the line structure corresponding to the real gas absorption spectrum, which is maintained with fixed spectral intervals in non-uniform medium with the help of the reference approach. The validation of the SLW-1 model is performed by comparison with (i) benchmark solutions obtained by the line-by-line method and (ii) the SLW method with a large number of gray gases. Formulation of the SLW-1 method is also shown with the Two-Flux method and P-1 differential approximation.     

利用可调谐激光吸收光谱技术对光路上气体温度分布的测量

利用可调谐激光吸收光谱技术(TDLAS),扫描多条吸收谱线以实现气体温度分布的测量。文章给出了温度分布测量的原理和方程离散化的方法,在气体浓度和压力均匀时,利用带约束最小二乘法计算得到温度分布。根据HITRAN中6 330 cm-1附近的4条CO谱线的参数,建立了温度在300和600 K时,路径长度均为55 cm的两段温度分布模型,模拟了测量误差与温度区间长度约束条件的影响。结果表明随着测量误差的增大和约束条件的减弱,计算结果误差相应增大。在5％的测量误差下,计算结果的最大误差为11％,平均误差为2.2％。以管式炉中的高温段和室温下的低温段作为两段温度分布模型进行试验。利用6 330 cm-1处的垂直腔面发射激光二极管(VCSEL)扫描得到的4条CO谱线,通过背景信号的三次多项式拟合得到基线,求出温度分布计算所需的光谱吸收率积分值。在四种情况下, 计算温度分布结果与模型误差分别为7.3％,6.5％,4.7％和2.7％。     

Many-body effects on intersubband resonances in narrow InAs/AlSb quantum wells

Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (QW) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons. The oscillator strength of intersubband resonances (ISBRs) strongly varies with QW parameters and electron density because of this coupling. Using the intersubband semiconductor Bloch equations for a two-conduction-subband model, we show that intersubband absorption spectra for narrow wells are dominated by the Fermi-edge singularity (via coupling to repellons) when the electron gas becomes degenerate and in the presence of large nonparabolicity. Thus the resonance peak position appears at the Fermi edge and the peak is greatly narrowed, enhanced, and red shifted as compared to the free particle result. Our results uncover a new perspective for ISBRs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBR line shape.     

一种气体吸收的逐线计算模型及其实验验证

建立一种高分辨率的气体吸收光谱的逐线计算模型,分子谱线参数数据库采用了最新的低温库HITRAN2008和高温库HITEMP2010,能根据温度条件自动选择合适的谱带参数库,并可同时满足高温和常温气体辐射计算。计算波数采用等间隔取样,取样间隔大小以能分辨出典型分子谱线为条件确定。线翼截断采取等波数截断,总内配分函数由Gamache拟合三次多项式计算。谱线线型根据气体温度和压力来选择,最后,利用该模型计算了压力为1atm,不同温度、浓度和路径长度下CO2在4.3μm和2.7μm的透射率。考虑FTIR仪器增宽,将逐线计算结果降为窄带透射率,与中分辨率的试验结果对比均吻合,并能在较宽的温度范围内保证精度。     

Calculating vibrational mode contributions to sound absorption in excitable gas mixtures by decomposing multi-relaxation absorption spectroscopy

Sound relaxational absorption spectroscopy of excitable gas mixtures is potentially applied for gas composition detection. The relaxation of vibrational modes of gas molecules determines the sound relaxational absorption. However, to our knowledge, the contribution of each vibrational mode available in gas mixtures to sound multi-relaxation absorption has not been calculated in existing literature. In this paper, based on the decoupled expression of the effective isochoric molar heat for a gas mixture, a sound multi-relaxation absorption spectrum is decomposed into the sum of single-relaxation spectra. From this decomposable characteristic, the contribution of each vibrational mode available in the gaseous medium to the multi-relaxation absorption is obtained at room temperature. For various gas compositions including carbon dioxide, methane, nitrogen etc., the calculated contributions of vibrational modes are verified by the comparison with experiment data. We prove the following views with quantifiable outcomes that the primary molecular relaxation process associated with the lowest mode plays the major role in acoustic relaxational absorption of gas mixtures; the mode with lower vibrational frequency provides higher contribution to the primary relaxation process. This work could provide a deeper insight into the relationship between the sound relaxational absorption spectroscopy and gas molecules.     

Emission and absorption of neutrinos by nonrelativistic neutrons in a magnetic field

The neutrino luminosity of a nonrelativistic nondegenerate neutron gas in a magnetic field owing to the flip of an anomalous magnetic moment, as well as the mean free path of the neutrino due to the absorption in a magnetized neutron gas, has been calculated using the neutron density matrix in the magnetic field obtained in this work. The Fermi energy and partial concentrations of the degenerate neutron gas in the magnetic field have been determined. The astrophysical applications are discussed.     

InSb纳米晶体的生长和吸收光谱的研究

采用在惰性气体中蒸发的方法获得了沉积在ZnS基片上的InSb纳米晶体,其平均尺寸随惰性气体的压强增加而增大.从实验测量的室温吸收谱上看到,当纳米晶体的平均直径从27.9 nm减小到24.2nm再到21.4 nm时,其吸收边分别向高能方向移动了0.0151 eV和0.0145 eV.用有效质量近似模型计算了半导体纳米晶体的吸收边相对其体材料的移动,将理论计算与实验结果进行了比较.     

DOAS烟气测量系统的温度非线性补偿方法

基于紫外差分吸收光谱技术,针对温度对烟气浓度测量的影响,提出一种非线性补偿方法.在紫外波段200-230nm波长范围内,以SO2和NO标准气体为研究对象,从50℃到90℃间隔10℃变化测量其吸收光谱,利用多项式拟合的方法计算气体差分吸收截面,研究温度与吸收截面的定性和定量关系.实验结果显示,不同波长点的两种气体吸收截面随温度变化呈非线性关系.采用非线性补偿修正后,SO2和NO的测量误差明显减小,该方法可提高烟气测量的准确度.     

Modelling of free radicals production in a collapsing gas-vapour bubble

This paper deals with a model linking bubble dynamics under an acoustic pressure field and production of free radicals in the resulting collapses of this bubble. The bubble dynamics model includes interdiffusion of gas and vapour in the bubble as well as evaporation or condensation at the interface, and it assumes uniformity of the internal pressure and perfect gas law for the gas vapour mixture. At the maximum compression of the bubble, all the reactions of dissociation which can occur are assumed at thermodynamic equilibrium. The local composition (especially in free radicals) in the bubble is then calculated by an algorithm based on free energy minimization using the information concerning the maximum compression provided by the bubble dynamics model resolution. Using this model a comparison of free radicals production has been made for two different driving frequencies (20 kHz and 500 kHz), and at given bubble radius and acoustic pressure, an optimum of liquid bulk temperature has been derived for the production of free radicals very similar to the experimental one concerning oxidation reactions in aqueous phase.     

Excess ultrasonic absorption in H2O-D2O mixture

The two state model of Hall (1948) and new relations for the relaxation time and structural compressibility were used to calculate the ultrasonic absorption in excess of the classical values of H₂OD₂O mixture at 30°C. There is good agreement between the calculated and experimental values of excess absorption. The molar free energy difference and the molar volume change calculated for the open-packed and close-packed states agree well with the values reported by Kor et al. (1972).     

Two photon coherence and pumping in infrared doppler free molecular spectroscopy

The calculation of the gas bulk polarization in Doppler free two photon interaction is recast within a simple model. Two photon coherence and pumping effects are clearly distinguished. Some new features of absorption and refractive index are pointed out for strong two photon saturation.     

PETN炸药爆轰产物状态方程的理论研究

 采用van der Waals等效单组分流体模型和Ross硬球微扰理论软球修正模型,计算爆轰气相产物的状态方程;用石墨相、金刚石相、类石墨液相和类金刚石液相4种相态描述凝聚成分,由Gibbs自由能最小原理确定不同状态下的凝聚产物相态。对爆轰产物混合系统采用自由能最小原理,通过化学平衡方程组求解炸药爆轰产物系统的平衡组分。使用该理论计算PETN炸药Chapman-Jouguet（CJ）点的爆轰参数,其值与实验值符合得很好;同时计算了以CJ点为起始点的等熵卸载线,并与传统的Jones-Wilkins-Lee（JWL）状态方程的计算结果进行比较,发现计算的γ值是单调递减的,而JWL状态方程计算的γ值却出现了“双峰”现象。分析认为,传统的JWL状态方程给出的“双峰”变化,是由其函数形式自身决定的,并不对应实际物理过程。     

烟道气体SO2光谱辐射强度和吸收系数的研究

采用乘积近似法构建配分函数合理模型,计算了SO₂分子的总配分函数.利用所得的配分函数、将常温下的无转动跃迁矩平方近似为一常数并应用于高温及Herman-Wallis因子系数,编制光谱程序,计算了烟道气体SO₂分子三个主要跃迁带100-000、001-000和101-000不同温度段的光谱强度和吸收系数.结果表明,计算所得的配分函数和谱线强度与数据库相比,不管是常温296 K还是高温3000 K,都吻合较好,相对偏差都在3%以下,这说明构建的配分函数模型和编制的程序是可靠的,在此基础上,进一步计算了各跃迁带在不同温度的吸收系数.从模拟光谱图可看出,强度随着温度升高明显减小,谱带带心没变,峰值波数向两边偏移;吸收系数随着温度升高也减少,其中在3000 K以下吸收峰位置增宽,到高达4000 K以上基本不再变换,这为监测烟道气体环境污染提供实验和理论参考.     

高温稠密气态混合物质压强的计算

 基于含温有界相对论自洽场平均原子模型,计算了高温稠密条件下气态混合物的压强。通过求解相对论Dirac方程给出有界原子的电子波函数和轨道能量。电子在各单电子轨道上的平均占据数服从Fermi-Dirac分布。以铝、铝镁混合物、铁和高能炸药HMX（奥克托金）为算例,计算了在一些温度密度点下的压强并给出了分析。     

烟道气体SO2光谱辐射强度和吸收系数的研究

采用乘积近似法构建配分函数合理模型,计算了SO2分子的总配分函数.利用所得的配分函数、将常温下的无转动跃迁矩平方近似为一常数并应用于高温及Herman-Wallis因子系数,编制光谱程序,计算了烟道气体SO2分子三个主要跃迁带100-000、001-000和101-000不同温度段的光谱强度和吸收系数.结果表明,计算所得的配分函数和谱线强度与数据库相比,不管是常温296K还是高温3000K,都吻合较好,相对偏差都在3%以下,这说明构建的配分函数模型和编制的程序是可靠的,在此基础上,进一步计算了各跃迁带在不同温度的吸收系数.从模拟光谱图可看出,强度随着温度升高明显减小,谱带带心没变,峰值波数向两边偏移;吸收系数随着温度升高也减少,其中在3000K以下吸收峰位置增宽,到高达4000K以上基本不再变换,这为监测烟道气体环境污染提供实验和理论参考.     

Mean free path of nucleons in a Fermi gas at finite temperature

The mean free path of a nucleon in a nuclear Fermi gas at finite temperature is calculated by utilizing the free nucleon-nucleon cross section modified to suppress final states excluded by the Pauli principle. The results agree with an earlier zero-temperature calculation but yield substantially smaller values than a previous finite-temperature analysis.The Fermi gas mean free paths are some two to four times shorter than those implied by phenomenological imaginary optical potentials, suggesting that the present Fermi gas model fails to adequately describe the physical processes determining the mean free path. Even so, the present results, taken as lower bounds on the mean free path, require temperatures of some 4.5 MeV before the mean free path of bound nucleons becomes as short as the nuclear diameter. It follows that very high excitation energies are prerequisite to any short mean free path assumption in nuclear heavy-ion collisions.     

Competition of Short-Range and Long-Range Mechanisms of Spectral Line Broadening in Emission of Atomic and Molecular Gases

An analogy is shown for broadening the spectral line of atoms in the case of competition between the short-range Doppler broadening mechanism and the long-range impact mechanism in atomic gases, as well as for the absorption band of a molecular gas in the infrared (IR) region of the spectrum, where the longrange part of the spectrum is also determined by the impact mechanism of the broadening. The long-range part in the pedestal region of the absorption band is associated with the distribution of molecules over the rotational states, and, in the range of wings of the absorption band, it is due to a finite time of collisions between emitting and perturbed molecules. The flux of resonant radiation produced by an excited atomic gas is estimated using the concepts of the spectral absorption band and a large optical thickness of the gas. These concepts are used for a molecular gas where, in the framework of the regular model (the Elsasser model), expressions are given for the absorption coefficient related to a specific spectral absorption band, separately in the pedestal region and for wings of the absorption band. As a demonstration of the possibilities of these concepts, the IR flux is calculated on the surface of Venus from its atmosphere, which includes seven vibrational transitions of the carbon dioxide molecule and amounts to 26% of the total flux of IR radiation emitted by the Venus surface. An analysis of the Venus energy balance leads to the conclusion that the main part of IR radiation of the Venus atmosphere falling on its surface is formed by a microscopic dust in the Venus atmosphere. This channel of the Venus energy balance is realized if the mass of a microscopic dust in the Venus atmosphere is seven orders of magnitude less than the mass of atmospheric carbon dioxide.