Experimental study of the dynamics of front propagation in the Co(OH)2/NH4OH Liesegang system using spectrophotometry

In this paper we study the temporal dynamics of the Co(OH) 2/NH 4OH Liesegang system with redissolution by complex formation with ammonia using UV-vis spectrophotometry with a special setup. The formation of precipitate bands is accompanied with band redissolution at the top, and because of such precipitation-redissoultion dynamics, the bands appear as a propagating wave. The spectrophotometric technique developed in this study allows us to study at the kinetics of formation of the bands and their redissolution in great details. The formation, growth, and dissolution of multiple bands are monitored by the time evolution of the absorbance. It was found that the individual band formation is sudden and takes between 15 min to half an hour to form before the next band appears. The speed of formation of bands was different for different bands and the maxima of these speeds fit a Gaussian curve. The content of cobalt hydroxide in these bands was calculated and is shown to increase to a maximum away from the interface and then decreases. The bands later grow by further precipitation. This growth was demonstrated to be nonlinear in time. On the other hand, the dissolution of bands was shown to take place simultaneously and collectively among the multiple bands under study. The effect of the concentration of Co (+2) ions on the dynamics of band formation and dissolution was studied. A time law for this Liesegang system was also determined. The system was also found to be very sensitive to temperature fluctuations.     

On the origin of the intensity of the resonant raman bands of differing polarization in heme proteins

It is shown that depolarized and inverse polarized bands dominate the resonance Raman spectrum of heme proteins when the scattering derives its intensity from different electronic transitions (the and Soret bands), while th polarized bands dominate the spectrum when the incident light is resonant with only the strong Soret band.     

Influence of electronegative substituents on the electronic spectra of the porphyrins in the form of dications

The positions of the electronic absorption bands and also the intensities of the Soret bands of the porphyrins with ethoxycarbonyl substituents in the form of dications have been calculated by the LCAO MO method in Huckel's approximation. Comparison with the experimental results shows good agreement.     

A Raman spectroscopic study of the uranyl sulphate mineral johannite

Raman spectroscopy at 298 and 77K has been used to study the secondary uranyl mineral johannite of formula (Cu(UO2)2(SO4)2(OH)2 x 8H2O). Four Raman bands are observed at 3593, 3523, 3387 and 3234cm(-1) and four infrared bands at 3589, 3518, 3389 and 3205cm(-1). The first two bands are assigned to OH- units (hydroxyls) and the second two bands to water units. Estimations of the hydrogen bond distances for these four bands are 3.35, 2.92, 2.79 and 2.70 A. A sharp intense band at 1042 cm(-1) is attributed to the (SO4)2- symmetric stretching vibration and the three Raman bands at 1147, 1100 and 1090cm(-1) to the (SO4)2- anti-symmetric stretching vibrations. The nu2 bending modes were at 469, 425 and 388 cm(-1) at 77K confirming the reduction in symmetry of the (SO4)2- units. At 77K two bands at 811 and 786 cm(-1) are attributed to the nu1 symmetric stretching modes of the (UO2)2+ units suggesting the non-equivalence of the UO bonds in the (UO2)2+ units. The band at 786cm(-1), however, may be related to water molecules libration modes. In the 77K Raman spectrum, bands are observed at 306, 282, 231 and 210cm(-1) with other low intensity bands found at 191, 170 and 149cm(-1). The two bands at 282 and 210 cm(-1) are attributed to the doubly degenerate nu2 bending vibration of the (UO2)2+ units. Raman spectroscopy can contribute significant knowledge in the study of uranyl minerals because of better band separation with significantly narrower bands, avoiding the complex spectral profiles as observed with infrared spectroscopy.     

Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide-water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 A was observed with subtle differences whether the kaolinite was expanded with formamide or formamide-water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm(-1). These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm(-1) Raman band separated into two bands at 3633 and 3625 cm(-1). DRIFT spectra showed the hydroxyl deformation mode at 905 cm(-1). Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm(-1) attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm(-1) and are attributed to the amide 1 and amide 2 vibrations.     

Analysis of composite bands in the electronic absorption spectra of compounds in solutions

Appearance of composite bands consisting of two individual bands with different half-widths in the course of resolution of absorption spectra was analyzed.     

A Low-Frequency Infrared Study of the Reaction of Methoxymethylsilanes with Silica

A thin film infrared technique is used to observe bands due to hydrogen-bonded and chemisorbed methoxymethylsilanes on fumed silica in the low-frequency region below 1300 cm(-1). The low-frequency region contains the characteristic bands due to Si-O-Si, Si-O, Si-C, Si-CH(3), and SiO-C modes. Band assignments are aided by ab initio calculations and comparison to thin film experiments of adsorbed chloromethylsilanes. The spectral interpretation was expected to be more complicated than that of the corresponding chlorosilanes because the strong SiO-C alkoxy bands lie in the same region as the Si-O-Si bands. However, the SiO-C bands are weak in intensity when participating in hydrogen-bonding interactions enabling easy detection of the Si-O-Si bands due to chemisorbed species. By combining the low-frequency data with the spectral information for the hydroxyl region, a clearer picture of the nature of the bonding to the surface is obtained. When adsorbed at room temperature, all methoxy groups participate in hydrogen bonding with the surface hydroxyl groups. When the reaction is performed at 150 degrees C, the silanes are chemisorbed via a Si-O-Si bond and the remaining methoxy groups of the chemisorbed species are hydrogen bonded to the surface hydroxyl groups. At reaction temperature of 400 degrees C there is no evidence of hydrogen bonding but the spectra are complicated by the reaction of methanol with the surface. Copyright 2000 Academic Press.     

Reconsideration of the electroabsorption spectrum of the anthracene crystal

A non-linear least-squares procedure is applied directly to resolve the electroabsorption spectrum of anthracene into individual bands. Statistical tests and recent theoretical results are used to determine the number of bands. The band at around 3.68 eV is confirmed and two new bands are detected at 3.842 and 4.023 eV.     

Variable temperature photoelectron spectroscopy. The adiabatic ionization potential of the iodine molecule

Vibrational structure is resolved in the first two bands in the Ne I photoelectron spectrum of iodine. The adiabatic IP is established by temperature variation, and spectroscopic IP for both bands are found to correspond to production of ions with three vibrational quanta. A photoionization value for the first IP corresponds to ions with two vibrational quanta. Structure is also observed in the corresponding bands of iodine bromide.     

FTIR investigation of the conformational properties of the cyanide bound human hemoglobin

Infrared spectra at 4 cm⁻¹ resolution of the cyanide ligated human methemoglobin (Hb-CN) were examined in the C---N stretching region. The FTIR spectra of hemoglobin ligated with the various isotopomeric forms of the cyanide ion support the existence of three conformational states for Hb-CN. In potassium phosphate buffer at pH of 7.5, the three bands were observed at 2116, 2122 and 2127 cm⁻¹ for natural abundance Hb-CN. These bands shift to 2086, 2091 and 2095 cm⁻¹ for Hb-¹²C¹⁵N and 2073, 2077 and 2081 cm⁻¹ for Hb-¹³C¹⁴N. Two extra bands have been identified in the IR spectra of solid Hb-CN in KBr pellets. The peaks persist in the pH range between 3.5 and 10.5 with small changes in frequency and intensity. The appearance of several C---N stretching bands is consistent with C---N vibrators residing in different environment and support the hypothesis that Hb-CN assumes multiple conformers under the conditions studied.     

The circular dichroism spectra of the β-cyclodextrin complex with azulene

When azulene is included in the cavity of β-cyclodextrin (β-CDx), induced circular dichroism (CD) bands are observed in the corresponding absorption bands of azulene. On the basis of the theoretical conclusions for β-CDx complexes with naphthalene derivatives of Harata and Uedaira, it is concluded from the signs of the CD bands that the first (about 455 to 715 nm), third (about 290 to 305 nm) and fifth (at about 238 nm) absorption bands have the transition dipole moments perpendicular to the long axis and the second 305 to 360 nm), fourth (about 240 to 290 nm) and sixth (shorter than 220 nm) absorption bands have the transition dipole moments parallel to the long axis of azulene. Our assignments are in complete agreement with earlier assignments. Our experimental results do not provide any information regarding two new electronic transitions suggested theoretically by Thulstrup et al.     

Determination of shifts by means of the absolute area of the difference spectrum: cases of non-rigorous application of the theory

The method of determination of spectral shifts by use of the absolute area of the difference spectrum, previously developed in several papers, holds rigorously when the bands to be compared either have same profiles or are both symmetrical. It often happens in practice that none of these conditions is fulfilled and the concept itself of spectral shift is then questionable. However, it is possible to define in any case quantities, which, in the rigorous cases of definition of the spectral shift, are equal to each other and to the spectral shift. These quantities are the shift between the maximum intensity of the bands, the distance between vertical lines sharing the area of the bands into two equal parts, the displacement which must be given to one of the bands to reach the minimum of the absolute area of the difference spectrum. They are determined for a series of couples of model profiles, one of them being more and more dissymmetrical. Their values are compared with the approximate spectral shifts given by the application of the absolute area method. It is shown that up to relatively important dissimilarity of the profiles, the values of all these quantities are very close and may be taken as the spectral shift. Moreover, an extrapolation method giving the shift between the maximum intensities of dissimilar and dissymmetrical bands is given.     

The dependence of the intensity of Raman bands of pyridine at a silver electrode on the wavelength of excitation

On increasing the wavelength of excitation over the range 350–700 nm, Raman bands of pyridine adsorbed at a roughened silver electrode are found to increase in intensity, relative to bands of the bulk medium (aqueous perchlorate or liquid pyridine) in contact with the electrode. The increase is observed in the bands at 1000–1050 cm^?1 and 1600 cm^?1 due to ring stretching, and similar increases are observed in other bands of the surface species, notably those due to CH stretching (3076 cm^?1), b₂ ring deformation (669 cm^?1, and AgN stretching (239 cm^?1, which have not been reported previously.     

Raman and infrared spectroscopy of the manganese arsenate mineral allactite

The mineral allactite [Mn(7)(AsO(4))(2)(OH)(8)] is a basic manganese arsenate which is highly pleochroic. The use of the 633 nm excitation line enables quality spectra of to be obtained irrespective of the crystal orientation. The mineral is characterised by a set of sharp bands in the 770-885 cm(-1) region. Intense and sharp Raman bands are observed at 883, 858, 834, 827, 808 and 779 cm(-1). Collecting the spectral data at 77K enabled better band separation with narrower bandwidths. The observation of multiple AsO(4) stretching bands indicates the non-equivalence of the arsenate anions in the allactite structure. In comparison the infrared spectrum shows a broad spectral profile with a series of difficult to define overlapping bands. The low wavenumber region sets of bands which are assigned to the nu(2) modes (361 and 359 cm(-1)), the nu(4) modes (471, 452 and 422 cm(-1)), AsO stretching vibrations at 331 and 324 cm(-1), and bands at 289 and 271 cm(-1) which may be ascribed to MnO stretching modes. The observation of multiple bands shows the loss of symmetry of the AsO(4) units and the non-equivalence of these units in the allactite structure. The study shows that highly pleochroic minerals can be studied by Raman spectroscopy.     

导电高聚物聚吡啶的电子能带及其结构研究

聚吡啶(简称PPy)易于进行n-型掺杂并使其电导率大大提高,可用于制作高聚物电池的负极,本文将PPy视为准一维体系,采用EHMO/CO方法计算了新合成的导电高分子材料--聚吡啶4种可能构型的电子能带。     

Problems in the IR measuring the acidity of zeolite bridging hydroxyls by low-temperature CO adsorption

Two infrared OH stretching bands are produced after interaction of CO with H-ZSM-5 bridging hydroxyls. These two bands are not due to heterogeneity of the acid sites but arise from Fermi-resonance.     

卤化氢共振增强多光子电离光谱

测定了卤化氢(HCl, HBr 和HI) (2+1)共振增强多光子电离(REMPI)光谱, 采用模拟计算法分析推导出转动常数、谱带源以及Ω态振动谱带的同位素位移值. 得到的HCl数据同Green等人用常规分析法所推导的结果极为吻合. 得出8条振动谱带,其中包括V(¹∑⁺)态, E(¹∑⁺)的v'=4态以及HBr的5个新谱带, 此外还推导出HI的E态v'=1的4个振动谱带光谱参数. 观测了V和E态之间因同类相互作用而产生的不规则能级间距、转动参数和同位素位移. 讨论了HCl和HBr的E态和V态振动谱带中的转动谱线序列O和S对Q的强度比变化,提出了双光子激发机理.     

Modification of the Kaolinite Hydroxyl Surfaces through the Application of Pressure and Temperature, Part III

Kaolinite hydroxyl surfaces have been modified by the combined application of heat and pressure in the presence of water at 120 degrees C and 2 bars and at 220 degrees C and 20 bars. X-ray diffraction shows that some of the layers are expanded. It is hypothesized that this expansion occurs at the edges of the crystals due to the intercalation of water. The X-ray diffraction data is supported by diffuse reflectance infrared spectroscopy, with additional hydroxyl stretching bands observed around 3550 and 3590 cm-1. These bands are attributed to adsorbed water and to edge-intercalated water. Additional bands are observed in the hydroxyl deformation region around 895 and 877 cm-1. The position of these bands depends on the defect structure of the kaolinite and the conditions under which the kaolinite was thermally treated. Additional water bending vibrations were observed at 1651 and 1623 cm-1 for the thermally treated high-defect kaolinite and at 1682 and 1610 cm-1 for the low-defect kaolinite. The bands at 1651 and 1682 cm-1 are attributed to the bending modes of water coordinated to the kaolinite surface. The role of water in the edge intercalation of water in the high- and low-defect kaolinites is apparently different. Copyright 1999 Academic Press.     

顺铂与F-肌动蛋白的结合方式的LMCT谱研究

本文根据顺铂及顺铂与F-肌动蛋白电子光谱中电荷转移谱带研究了顺二氨合铂(II)离子与F-肌动蛋白的结合方式及构型.将所得光谱解极为个别吸收谱带,并与按不同构型、不同配位原子计算结果相比较,结果表明,铂以平面四方形构型主要与两个氨分子、一个硫和一个氨基氮配位.     

Comparison of the relative intensities of penning electron spectrum and photoelectron spectrum. Unsaturaated hydrocarbons

The Ne* (³P₂) Penning electron spectra and the Ne I photoelectron spectra of ethylene, benzene, 1,3-butadiene, and styrene were compared. The π bands in the Penning spectra showed enhancement relative to the σ bands in comparison with the corresponding photoelectron spectra, suggesting that Penning electron spectroscopy has potential value for the assignment of photoelectron bands.