Detection of phase transitions in heavy silane by i.r. spectroscopy

An i.r. spectroscopic study of SiHD₃ isolated in SiD₄ reveals an apparent second-order phase transition at 38 K. In the lowest-temperature phase the SiD₄ molecules probably occupy two sites of C₁ symmetry. Between 38 K and 67 K the SiD₄ molecules probably occupy one site of C_s symmetry.     

Raman band shapes and the dynamics of liquid N2O4

The Raman spectra of the totally symmetric A _g modes, v ₁, v ₂ and v ₃, of the N₂O₄ molecule have been measured in the liquid state at 262, 279 and 297 K. The vibrational and the rotational correlation functions are calculated. The long-time exponential decay of the rotational correlation functions of all the A _g modes reflects an asymptotic diffusional behaviour of molecular reorientation. The rotational relaxation rate is found to increase with increasing temperature. A marked point of inflection from the short time inertial correlation to the long time exponential decay appears at about 0·35 ps for the v ₂ mode. This is an indication of orientational rebound arising from the librational motion in a temporary solvent cage. The isotropic bandwidth increases in the order v ₁ < v ₂ < v ₃, which is also the order of decreasing vibrational frequency. The temperature dependence of the peak frequency and of the bandwidth are also found to increase in the same order. These observations are analysed qualitatively in terms of two models of vibrational dephasing which take into account the effect of vibrational anharmonicity.     

The influence of high-frequency phase distortion on the phase correction effect in atmospheric turbulence

By using the method of the power-spectrum inversion, the turbulence phase screen has been built up, and the propagation characteristics of high-frequency phase of laser beam in atmospheric turbulence have been analyzed; in addition, the phase correction effect of laser beams by using the adaptive deformable mirror has been simulated, and its affecting factors in turbulence have also been analyzed quantitatively. The results show that the phase correction effect of laser beams in turbulence is mostly determined by the percent of high-frequency phase in distorted wavefront. With the increase of the intensity of atmospheric turbulence and the propagation distance in turbulence, the percent of high-frequency phase in distorted wavefront increases, resulting in the degradation of the phase correction effect.     

Influence of line interference on the vibration-rotation band shapes

The shapes of the CO, v₃, CO₂, and v₃ N₂O fundamental vibration-rotation bands have been studied at various temperatures and in the presence of several perturbing gases. Also the half-widths of CO vibration-rotation lines have been measured at 78 K. In the region of line wings, the measured absorption coefficients deviate from those given by the superposition of Lorentzian profiles. These deviations are explained by the collision-induced line interference that causes redistribution of absorption inside the band. A theory of line mixing is formulated which is based on Markov approximation and on the strong collision model. Simple analytical expressions are obtained for the band shape. The computed shapes are in satisfactory agreement with the experimental results. The deviations from the Lorentz absorption observed in pure CO and in CO-N₂ at low temperature are partially ascribed to the formation of van der Waals dimers.     

Middle i.r. spectrum of the human epidermis

We measured the infrared transmittance spectrum of the human epidermis and correlated it with the irradiance spectra of: (i) the sun at sea level and (ii) an artificial source. In case (ii) the energy absorption rates within the epidermis can be orders of magnitude greater than in case (i). The data obtained by infrared spectroscopy can increase our understanding of the microscopic mechanisms that lead to pathological and therapeutic effects of infrared radiation.     

Optical absorption of irradiated quartz in the near i.r.

The effects of irradiation with 10 MeV electrons on the absorption spectra in the 3 μm region of both natural and synthetic quartz were investigated in the temperature range from 12 to 300°K. Six different types of synthetic crystals were included in this study. It was found that the spectra of samples that were treated by electrodiffusion were least affected by the irradiations, whereas large changes were observed in the spectra of untreated specimens. Lines were introduced by irradiation in some synthetic samples at 3306 and 3367 cm^?1. The dependence of the spectra on radiation dose was studied up to 6700 MRad. The largest spectral changes saturated above a dose of 200 MRad. The sharp, intense lines at 12°K were observed to broaden and weaken as well as to shift to shorter wavelengths as the temperature was raised to 300°K. Some of these effects can be described in terms of a model involving charge compensation of the aluminum defect by hydrogen and alkali metal ions. It is also found that, based on the spectra of unirradiated material, one can differentiate between natural, synthetic and swept synthetic crystals.     

High-frequency phase recovery of distorted wavefront and analysis on phase correction effect

By constructing a distorted wavefront with random phase screen, the correction process of distorted wavefront has been simulated, and the correction effect of deformable mirror has been simulated and analyzed with the method of high-pass filtering. The variations of correction effect and high-frequency phase distortion have been quantitatively analyzed. The results show that the beam quality of the corrected beam degrades obviously with the increase of high-frequency phase. In addition, a new method has been presented to recover the high-frequency phase of distorted wavefront according to the given intensity distribution and low-frequency phase in near field and the intensity distribution in far field. It shows that the method is very effective to recover the high-frequency phase of distorted wavefront.     

Theoretical i.r. emission spectra for the lower stratosphere

A direct method of integration of the transfer equation is developed for a concentration distribution model of gaseous constituents. The method is applied to the lower stratosphere and to the constituents H₂O and O₃. The results are presented in the form of synthetic luminance spectra in the far i.r. range from 50 to 100 cm_?1. This method may be extended to other constituents and applied in different spectral ranges.     

An i.r. study of heavy phosphine in the solid state

The near i.r. spectra of PD₃ and of PHD₂; isolated as a point defect in PD₃ have been obtained. Analysis of these spectra indicates that PD₃ exists in at least two crystalline forms. In the low-temperature form the molecules probably occupy two sets of sites of C_s. symmetry. A first-order phase transition accompanied by hysteresis occurs at 50 K and 60 K. This is most probably an order-disorder transition, because the spectrum of the high-temperature phase is that of a disordered crystal.     

Temperature dependence of the i.r. optical properties of LiF1

Essentially distortion-free imaginary dielectric index spectra have been obtained for LiF from Kramers-Kronig (KK) dispersion analysis of I.R. reflectance data at 300 K, 80 K and 20 K. The frequency dependence of the damping function as well as the temperature dependence of the various dispersion parameters of the first transverse optic mode have been illustrated. The effective damping constant $\text{}\text{?}$gg_o, and the resonance frequency ν_o, are found to be in satisfactory agreement with the theoretical calculations.     

Analysis of i.r. plasma reflectivity spectra: surface characterization

This paper demonstrates the utility of an analytical method recently suggested by the author for detecting the presence of a damaged surface layer on the top of a given sample.     

Non-linear dielectric effect in the isotropic phase of antiferroelectric liquid crystals

We have theoretically studied the non-linear dielectric effect in the isotropic phase of antiferroelectric liquid crystals on the basis of phenomenological theory. We find an analytical expression for the non-linear dielectric effect in the isotropic phase of the transition. The temperature dependence of the non-linear dielectric effect is presented in the isotropic phase of the transition.     

Non-linear dielectric effect in the isotropic phase of ferroelectric liquid crystals

We use a phenomenological model to find theoretically the non-linear dielectric effect (NDE) in the isotropic phase above the isotropic to chiral smectic-C (I-SmC^*) phase transition. We find an analytical expression for the NDE in the isotropic phase above the I-SmC^* phase transition. The temperature dependence of the NDE is presented in the isotropic phase of the I-SmC^* phase transition.     

Structural properties of aqueous electrolyte solutions from i.r. absorption spectra

Summary Results are reported on near-i.r. absorption spectra of H₂O in the presence of a variety of electrolytes, in the temperature range of liquid state. Spectra are analysed by using a deconvolution method, presented and discussed in previous works, thus obtaining a new level of detail and completeness of information. This allows for the first time the separation of solute perturbation on the solvent structure in terms of electric-field effects (common to all solutes), steric effects (mainly determined by the ionic radius) and more subtle effects due to the electronic structure of the specific ion. The quantitative set of spectroscopical parameters obtained for the different solutions in the whole explored temperature range offers a potentially useful ground for comparison with results of computer simulation.

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Riassunto In questo lavoro sono riportati risultati sugli spettri di assorbimento di H₂O nel vicino infrarosso in presenza di una varietà di elettroliti, nell'intervallo di temperatura dello stato liquido. Gli spettri sono analizzati usando un metodo di deconvoluzione, presentato e discusso in precedenti lavori, ottenendone un nuovo grado di risoluzione e completezza d'informazione. Questo ha permesso per la prima volta la separazione della perturbazione indotta dai soluti sulla struttura del solvente in termini di effetti di campo elettrico (comune a tutti gli ioni), effetti sterici (in media dipendenti dai raggi ionici) ed effetti piú fini dovuti alla struttura elettronica dei singoli ioni. Il quadro quantitativo dei parametri spettroscopici ottenuti per le differenti soluzioni nell'intervallo di temperature esplorato offre una base potenzialmente utile per un confronto con i risultati di simulazione al computer.

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Резюме Приводятся результаты для слектров инфракрасного поглошения H₂O в присутствии различных электролитов в области температуп жидкого состояния. Полученные спектры анализируются, используя метод ?развертывания?, предложенный в предыдуших работах с целью получения нового уровня полноты информации. Этот подход впервые позволил разделить возмушение, обусловленное растворенным вешеством на структуру растворителя, на эффекты электрического поля (обшие для всех растворенных вешеств), на сферические эффекты (зависяшие от радиуса иона) и на более тонкие эффекты, обусловленные электронной структурой отдельного иона. Количественная система спектроскопических параметров, полученных для различных растворов во всей исследованной области температур, представляет потенциально полезную основу для сравнения с результатами машинного моделирования.

     

Ultrasonic atomization: effect of liquid phase properties

Experiments have been conducted to understand the mechanism by which the ultrasonic vibration at the gas liquid interface causes the atomization of liquid. For this purpose, aqueous solutions having different viscosities and liquids showing Newtonian (aqueous solution of glycerin) and non-Newtonian behavior (aqueous solution of sodium salt of carboxy methyl cellulose) were employed. It has been found that the average droplet size produced by the pseudo-plastic liquid is less than that produced by the viscous Newtonian liquid having viscosity equal to zero-shear rate viscosity of the shear thinning liquid. The droplet size was found to increase initially with an increase in the viscosity up to a certain threshold viscosity after which the droplet size was found to decrease again. Also droplet size distribution is found to be more compact (uniform sizes) with an increasing viscosity of the atomizing liquid. The presence of the cavitation and its effect on the atomization has been semi quantitatively confirmed using energy balance and by the measurement of the droplet ejection velocities and validated on the basis of the decomposition of the aqueous KI solution. A correlation has been proposed for the prediction of droplet size for aqueous Newtonian fluids and fluids showing non-Newtonian behavior based on the dimensionless numbers incorporating the operating parameters of the ultrasonic atomizer and the liquid phase physico-chemical properties.     

Observation of thermally induced stress in amorphous semiconductors by i.r. crossed nicols

In thin slices of amorphous semiconductor Se₅₀Te₂₀As₂₀Ge₁₀, stress caused by switching was studied by crossed nicols method. The purely thermal effect due to the localized current flowing along the switching path is thought to be responsible for the stress by comparison with the experiment using focussed sun beam.     

Heusler合金Mn2NiGe马氏体相变的带Jahn-Teller效应研究

运用第一性原理的方法,计算磁性形状记忆合金Mn₂NiGe的晶体结构、磁结构、电子结构在马氏体相变中的变化.结果表明:Mn₂NiGe在发生马氏体相变时,产生了c轴拉长而a和b轴缩短的Jahn-Teller畸变,形成一个由两根长键和四根短键组成的拉长的八面体;伴随Jahn-Teller畸变,处于八面体中心的Mn离子的磁矩发生了显著的变化,而作为配体的Ni和Ge离子的磁矩基本不变;Jahn-Teller效应中Mn离子的e_g和t_2g能级的分裂,源自于晶体畸变所产生的配位场的改变,导致Mn离子d电子态密度的重新分布,从而在费米能级两侧打开一个赝能隙.