Anomalous atmospheric absorption spectra due to water dimer

The anomalous atmospheric absorption spectra in the window wavelength region of 8–14 um have been suggested due to the water dimer. Based on our laboratory measurements, water continuum CO₂ laser absorption spectra and a resonance absorption line due to the weak local water vapor pure rotational transition have been reported. The equilibrium concentration of water dimers in the atmosphere, the electronic binding energy and the theoretical calculations for absorption attenuation have been obtained in agreement with published data.     

Measurments of attenuation and refractive dispersion due to atmospheric water vapor at 80 and 240 GHz

Field line-of-sight propagation experiments were made at 80 and 240 GHz on a horizontal path of 810 m. The measured attenuations showed quadratic dependences on atmospheric water vapor density, and absorptions in excess of theoretical predictions were observed at both frequencies, while the measured refractive dispersion between these two frequencies showed a linear dependence on water vapor density and was in good agreement with theoretical prediction. Liebe's model for water vapor attenuation including empirical continuum absorption is confirmed to be effective for 80 and 240 GHz.     

Detection of the absorption spectra of water clusters under atmospheric conditions

The absorption spectrum of water clusters in the 5000–5300 cm^?1 range has been directly measured under laboratory conditions close to atmospheric conditions using the dynamical method for detecting water vapor in the metastable phase. It has been shown that detected absorption is primarily determined by water dimers.     

Theoretical investigation of the dependence of attenuation of pulsed laser radiation by fullerene-containing solutions on the pulse duration

The dependence of attenuation of laser radiation by fullerene-containing solutions on the laser pulse duration is theoretically studied. The investigation is carried out for a wide range of variations in the pulse durations: from 250×10^?15 to 10^?8 s. The contribution of two mechanisms (reverse saturable absorption and induced scattering associated with thermal nonlinearity) to the attenuation of radiation is studied. It is shown that reverse saturable absorption makes a considerable contribution to the attenuation in the whole range of durations under consideration, whereas induced scattering exists only in the range of durations that are longer than some nanoseconds. It is shown that the law of similarity with respect to the product of the intensity and the pulse duration for attenuation of laser radiation is approximately fulfilled in the whole range of durations, i.e., the attenuation depends on the energy density. Additionally, the elementary theory of reverse saturable absorption is developed and the limiting values of the absorption coefficient and the maximum attenuation are obtained.     

An approximate mean absorption coefficient for H2O

An approximate mean absorption coefficient was obtained for the rotation spectrum of H₂O from the Fourier transform of the molecular dipole autocorrelation function. The correlation function was calculated using classical mechanics to describe the rotation of the molecule. The expression for the absorption coefficient was parameterized to facilitate the determination of the temperature dependence of the absorption coefficient. A comparison was made between the classical and the quantum-mechanical calculations of the mean absorption coefficient for the pure rotation band of H₂O at 250, 300 and 500°K. The agreement between the classical and quantum-mechanical calculations may be improved if corrections for quantum effects are introduced into the classical calculations. A method is given for generalizing the results for the pure rotation band to the vibration-rotation bands. The mean absorption coefficient of water vapor was used to compute the thermal radiative flux in a heavy pure water vapor atmosphere. The results of these calculations were compared with those of an existing calculation in which the absorption due to water vapor was given by a gray approximation.     

Effect of Water Vapor Absorption on Measurements of Atmospheric Nitrate Radical by LP-DOAS

利用长程差分吸收光谱技术进行大气NO3自由基测量时,水汽的强烈吸收叠加在测量光谱中,对NO3的精确反演和探测限带来较大的影响. 通过分析水汽吸收的非线性效应,建立了一种去除水汽影响的有效方法. 通过测量日间大气吸收谱,并考虑日间水汽与夜晚水汽变化量,一同参与数据拟合,结果表明该方法可以有效地去除水汽吸收的影响. 把该方法应用于在珠三角外场实验中,获得了好的效果,探测限达到3.6 ppt。     

Density Functional Theory Study of Infrared and Ultraviolet Spectra of Urea L-Malic Acid

用密度泛函理论研究了新型二阶非线性光学晶体-L苹果酸脲.采用一些密度泛函理论方法计算了分子结构,比较得出PBEPBE/6-31+G(d,p)是计算分子结构的一种最佳的方法,然后给出了其红外和紫外可见光谱,并与实验结果作了比较,还结合分子轨道布局分析了紫外可见光谱. 同时结合极化连续模型利用密度泛函理论方法研究了L苹果酸脲在水中的几何结构及红外和紫外可见光谱,并指出了溶剂化效应对其性质的影响.     

Line shape in far wings and water vapor absorption in a broad temperature interval

Despite the long-term history of extensive studies on water vapor continuum absorption it can hardly be said that an exhaustive consideration has been given to this problem both from experimental and theoretical viewpoints. For instance, deficiency remains concerning the precise data on the absorption coefficient as a function of temperature, especially at reduced temperatures. New experimental data on water vapor continuum absorption in the 800-1250 cm⁻¹ spectral region at temperatures from 311 to 363 K have become available quite recently [15]. Two advanced variants of the line wing theory - asymptotic and quasistatic - are briefly outlined. The asymptotic line wing theory has been used successfully to describe the absorption coefficient both at elevated temperatures of the Baranov study and at the temperatures of earlier experimental data. Comparison is made with the results obtained from the quasistatic line wing theory.     

基于可调谐半导体激光吸收光谱的酒精蒸汽检测方法

采用窄带半导体激光器开展了酒精蒸汽浓度检测方法研究.使用酒精分子在7180 cm-1附近的一个相对较窄的吸收峰作为酒精分子的鉴别信息.为消除水汽对酒精分子检测的干扰,提出了建立多元线性回归方程拟合求解多分子吸收共存的问题.实验表明,系统的检测限达到25 ppm·m.     

Observation of a strong inverse temperature dependence for the opacity of atmospheric water vapor in the MM continuum near 280 GHz

Using atmospheric opacity measurements made at 278 GHz (9.3 cm^–1) at McMurdo Station, Antarctica during the austral springs of 1986 and 1987, combined with measurements of water vapor profile and total column density from near-simultaneous balloon flights, we have determined the attenuation per mm of precipitable water vapor (pwv) at this frequency. Our data were taken at significantly lower temperatures than other measurements in the literature for which accompanying water vapor pressure and temperature data are available. The results show a strong inverse dependence with temperature: measured opacity per mm of pwv is roughly a factor of two times greater at –35°C than at –10°C and three times greater than measurements at the same wavelength at +25°C reported by Zammit and Ade. We briefly review various theories proposed to explain excess absorption in continuum regions. Our lowtemperature measurements demonstrate a significantly greater inverse temperature dependence than embodied in several formulations, theoretical or empirical, proposed to represent mm-wave attenuation as a function of temperature and water vapor. The present results are qualitatively similar to observations of strong inverse temperature dependence in the near IR, but if attributed to water vapor dimer formation, imply a greater binding energy for the dimer than generally proposed by others. There is some independent evidence for a local anomaly in temperature dependence as a function of frequency near 280 GHz. It remains to be established whether our own results are strongly frequency dependent or apply generally to the mm-wave continuum.     

Sound waves in a liquid with polydisperse vapor–gas bubbles

A mathematical model is presented for the propagation of plane, spherical, and cylindrical sound waves in a liquid containing polydisperse vapor–gas bubbles with allowance for phase transitions. A system of integro-differential equations is constructed to describe perturbed motion of a two-phase mixture, and a dispersion relation is derived. An expression for equilibrium sound velocity is obtained for a gas–liquid or vapor–liquid mixture. The theoretical results agree well with the known experimental data. The dispersion curves obtained for the phase velocity and the attenuation coefficient in a mixture of water with vapor–gas bubbles are compared for various values of vapor concentration in the bubbles and various bubble distributions in size. The evolution of pressure pulses of plane and cylindrical waves is demonstrated for different values of the initial vapor concentration in bubbles. The calculated frequency dependence of the phase sound velocity in a mixture of water with vapor bubbles is compared with experimental data.     

Frequency-stabilized cavity ring-down spectrometer for high-sensitivity measurements of water vapor concentration

We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique capable of high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the ν₁+ν₃ water vapor combination band near ˜ν=7181.156 cm^-1, we compare spectroscopic and thermodynamic determinations of trace water vapor in N₂, and find systematic differences attributable to water vapor background effects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, the frequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1.2×10^-10 cm^-1 Hz^-1/2, which further corresponds to a minimum detectable water vapor mole fraction equal to 0.7×10^-9 for an absorption spectrum of 10 minutes duration. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Theoretical and experimental study of the ultrasonic attenuation in bovine cancellous bone

In this study a theoretical approach for the estimation of ultrasonic attenuation is proposed. The approach combines two models which take into account both absorption and scattering. Attenuation due to absorption is studied by using the Biot’s analytical model whereas that due to scattering is described by means of a generalized weak scattering model which is formulated for binary mixtures. The scattering model takes account of the density fluctuation of the porous medium in addition to the propagation velocity fluctuation. For the calculation of the attenuation coefficient due to absorption, experimental values have been used to link size of pores to porosity. The theoretical results have been compared with experimental data obtained on bovine cancellous bone samples filled with water. Using an immersion acoustic transmission method, the ultrasonic attenuation has been measured at a frequency range between 0.1 and 1.0 MHz for 12 bovine cancellous bone samples with a porosity range between 40% and 70%. The prediction of attenuation with this model appears to correspond more closely to its experimentally observed behavior. This study indicates that scattering is the predominant mechanism which is responsible for attenuation in trabecular bone. Furthermore, it shows that the density fluctuations contribute significantly to the phenomenon of attenuation and cannot thus be neglected.     

New measurements of the water vapor continuum in the region from 0.3 to 2.7 THz

We present a spectroscopic study of the water vapor continuum absorption in the far-IR region from 10 to 90 cm⁻¹ (0.3-2.7 THz). The experimental technique combines a temperature-stabilized multipass absorption cell, a polarizing (Martin-Puplett) interferometric spectrometer, and a liquid-He-cooled bolometer detector. The contributions to the absorbance resulting from the structureless H₂O-H₂O and H₂O-N₂ continua have been measured in the temperature range from 293 to 333 K with spectral resolution of 0.04-0.12 cm⁻¹. The resonant water vapor spectrum was modeled using the HITRAN04 database and a Van Vleck-Weisskopf lineshape function with a 100 cm⁻¹ far-wing cut-off. Within experimental uncertainty, both the H₂O-H₂O and H₂O-N₂ continua demonstrate nearly quadratic dependencies of absorbance on frequency with, however, some deviation near the 2.5 THz window. The absorption coefficients of 3.83 and 0.185 (dB/km)/(kPa THz)² were measured for self- and foreign-gas continuum, respectively. The corresponding temperature exponents were found to be 8.8 and 5.7. The theoretically predicted foreign continuum is presented and a reasonable agreement with experiment is obtained.     

Low-frequency sound absorption and attenuation in marine medium

Original experimental data are analyzed on the low-frequency sound attenuation in the Mediterranean, Black, and Baltic Seas, Sea of Japan, and the north-western region of the Pacific Ocean. In these regions, waters significantly differ in their temperatures and salinities. The analysis is aimed at obtaining an expression for calculating the low-frequency absorption coefficient in sea water. The analysis uses the previously published data on the measured (by the temperature discontinuity method) low-frequency relaxation times associated with boron present in sea water. The dependence of the absorption on the pH value (which was revealed in the 1970s) and the experimental data on sound absorption at frequencies higher than 5–10 kHz are also taken into account. As a result of the analysis based on the assumption that low-frequency relaxation takes place, an expression is proposed that relates the low-frequency absorption to the temperature, salinity, and pH value and equally well describes the experimental frequency dependences of attenuation for the four regions at hand (except for the Baltic Sea). Increased attenuation coefficients are noticed for shallow seas and deep-water regions where waters are influenced by intense currents, strait zones, and zones of mixing waters of different origin, i.e., for the ocean areas where, in addition to the attenuation, sound scattering by inhomogeneities of the marine medium and sound energy leakage into the sea floor are significant.     

Mössbauer scattering spectroscopy

The Mössbauer scattering spectra detected by γ-and X-radiation are investigated, and an analytical representation for the scattering integrals is given. It is shown that the use of Mössbauer scattering spectroscopy allows us to determine the interference amplitude, angular correlation function, Debye-Waller factor for Rayleigh scattering, Lamb-Mössbauer factors and linewidths for the source and scatterer, electronic attenuation coefficients of γ-and X-radiation for the scatterer, the total attenuation coefficient of γ-radiation for Rayleigh and Compton scattering, photoabsorption coefficient of γ-radiation in the scatterer and K-shell of⁵⁷Fe, resonance absorption coefficient of Mössbauer radiation, the thickness of the scatterer and the number density of Mössbauer elements in it. An experimental procedure for checking the difference in Lamb-Mössbauer factors for absorption and scattering of Mössbauer radiation is proposed.     

Nonlinear diffusion of water molecules in glycerol

The dependence of the concentration of water molecules in water vapor brought into contact with glycerol surface was measured in a time window of 10⁻¹–10³ s. An obvious nonlinearity of water molecule diffusion was found in a short time approximation (within a minute). A proposal is made with regard to the convective character of diffusion due to heat release during absorption.     

First-time lidar measurement of water vapor flux in a volcanic plume

The CO₂ laser-based lidar ATLAS has been used to study the Stromboli volcano plume. ATLAS measured water vapor concentration in cross-sections of the plume and wind speed at the crater. Water vapor concentration and wind speed were retrieved by differential absorption lidar and correlation technique, respectively. Lidar returns were obtained up to a range of 3 km. The spatial resolution was 15 m and the temporal resolution was 20 s. By combining these measurements, the water vapor flux in the Stromboli volcano plume was found. To our knowledge, it is the first time that lidar retrieves water vapor concentrations in a volcanic plume.     

基于MAX-DOAS测定大气紫外波段水汽的吸收及其对DOAS反演影响的评估

大气水汽的吸收强度从微波区域到可见蓝光区域逐渐降低,然而在紫外波段的吸收却经常被人忽略。多轴差分吸收光谱（MAX-DOAS）技术是一种被动光学遥感技术,可以同时反演气溶胶、多种痕量气体（如NO₂,SO₂,HCHO,HONO等）以及水汽,常用于区域大气立体分布及输送监测,具有成本低、时间分辨率高、稳定、可实时监测等特点。水汽是一种重要的温室气体,在紫外波段反演一些痕量气体时水汽的吸收经常不被考虑,可能对紫外波段痕量气体的反演造成影响,从而产生系统误差。介绍了基于MAX-DOAS对紫外波段大气水汽的反演,于2020年6月1日—9月24日在西安乾县进行观测,通过选取最优反演波段,并将反演结果与可见蓝光波段的水汽进行对比,证实了紫外波段存在水汽吸收,评估了紫外水汽的吸收对同波段痕量气体反演的影响。首先,根据不同拟合波段反演的水汽均方根误差（RMS）以及水汽和O₄的吸收截面情况,选取紫外和可见蓝光波段水汽的最优反演波段分别为351～370和434～455 nm。其次,通过DOAS拟合得到紫外和可见蓝光波段O₄和H₂O的对流层差分斜柱浓度（DSCD）, 分别将紫外和可见波段的O₄ DSCD和H₂O DSCD做相关性分析,两个波段O₄ DSCD的相关系数r=0.85,H₂O DSCD的相关系数r=0.80。为消除不同波段的辐射传输差异,将同波段的H₂O DSCD和O₄DSCD作比值,两个波段H₂O DSCD/O₄DSCD的相关系数r=0.89。紫外和可见蓝光波段H₂O DSCD/O₄DSCD的高相关系数表明,即使在相对沿海城市水汽浓度较低的西安市,在363 nm附近的紫外波段同样存在水汽吸收,这将会对采用DOAS技术在紫外波段反演其他痕量气体造成影响。最后,分别对可能受紫外波段水汽吸收影响的气体（O₄,HONO和HCHO）进行DOAS反演误差评估,紫外波段水汽的吸收将使O₄ DSCD,HONO DSCD以及HCHO DSCD在DOAS拟合过程中增加,分别对应于+1.16％,+8.55％和+9.04％的变化。     

Influence of temperature and ethanol content on aggregation of rhodamine 6G molecules in aqueous ethanol solutions

The effect of temperature on absorption spectra of Rhodamine 6G at concentrations of 10⁻⁶ and 10⁻³ M in water:ethanol solutions of various ethanol content was studied. The dimeric molecular fraction of Rhodamine 6G (10⁻³ M) was found as a function of temperature and ethanol content in the aqueous solution. It was shown that the absorption spectrum of Rhodamine 6G dimers (10⁻³ M) is dependent on temperature and ethanol content in the aqueous solution. Based on the relationship between J-and H-bands in the absorption spectrum of Rhodamine 6G dimers, both the angle between planes of associated Rhodamine 6G dye molecules and the free enthalpy of association were calculated. The structure of Rhodamine 6G dimers depends essentially on the ethanol content and aqueous ethanol solution temperature while experiencing the most temperature changes at an ethanol concentration of 25%. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 640–645, September–October, 2008.