Hydrate Single Crystals Research Articles

Melt growth and inhibition of ethylene oxide clathrate hydrate

Growth and inhibition of single crystals of ethylene oxide clathrate hydrate provide experimental accessibility to similar phenomena in methane clathrate hydrates. Ethylene oxide hydrate single crystals were grown from the supercooled melt as rhombic dodecahedra, exhibiting {1 1 0} as the slowest growing face. The addition of poly(N-vinylcaprolactam) (PVCap) or a random terpolymer of PVCap, poly(N-vinylpyrrolidone), and dimethylaminoethylmethacrylate causes small scale branching of crystals, but with a uniform crystal orientation. A few tenths of a weight percent of these additives cause complete crystal growth inhibition up to several degrees of supercooling.

Effect of guest–host interaction on Raman spectrum of a CO2 clathrate hydrate single crystal

The polarized Raman spectra of an artificial CO2 clathrate hydrate single crystal have been measured in order to examine the crystal-orientation dependence of the Raman spectra. Since the crystal had crystallographic facets, the orientation of the crystal was determined by using the Miller indices of the facets. When the angle θ between the polarization plane of the incident laser beam and the direction of one of the 〈110〉 axes of the single crystal varied, it was observed that the intensities of the peaks, which were caused by the Fermi resonance of the symmetric stretching mode and the overtone of the bending mode of CO2, and the O–H symmetric stretching vibration mode, varied with θ. Since the tetrakaidecahedron cage in the CO2 clathrate hydrate is distorted along the 〈100〉 axis, the variations of the scattering intensities of the CO2 have been calculated by using a simple model that assumes that the CO2 rotates on the {100} plane in the tetrakaidecahedron cage. The results obtained from the experiments are consistent with the calculations made by using this model. It has been concluded that the anisotropy of the peak intensities of the CO2 show the influence of the cage geometry on the motion of the guest molecule. The anisotropy of the O–H symmetric stretching vibration mode was interpreted with a five-body structure model. As the calculation with the model was consistent with the result obtained from the experiment, it was found that the anisotropy of the peak intensity of the O–H symmetric stretching vibration mode was related to the arrangement of the water molecules. We consider that the result indicates the influence of the motion of the guest molecule on the surrounding hydrogen-bonded network.

Melt growth of tetrahydrofuran clathrate hydrate and its inhibition: method and first results

Abstract Tetrahydrofuran clathrate hydrate single crystals grow from the supercooled melt as octahedra, showing that {1 1 1} is the slowest-growing face. The addition of poly(vinylpyrrolidone), poly(vinylcaprolactam) or a random terpolymer of the previous two with dimethylaminoethylmethacrylate causes the crystals to grow as hexagonal plates also bounded by {1 1 1} faces. Plate thickness decreases with increasing concentration of the impurity, until growth is altogether inhibited at a concentration of polymer that depends on supercooling.

Crystal-Orientation Dependence of Raman Spectra of Natural Air Hydrate Single Crystal

The polarized Raman spectra of a natural air hydrate single crystal from a deep ice core recovered at Dye-3 Greenland have been measured in order to examine the crystal-orientation dependence of the Raman spectra. Since the crystal had facets, the orientation of the crystal was determined by using the Miller indices of facets. When the angle θ between the polarization plane of the incident laser beam and the direction of [111] of the crystal varied, it was observed that the intensities of the stretching modes of the two major guest molecules (nitrogen and oxygen) varied with θ. Since the dodecahedron cage in the air hydrate are distorted along the 〈111〉 axis, the variations of the scattering intensities of N2 and O2 have been calculated by using a simple model that assumes N2 and O2 are on the plane of {111} in the dodecahedron cage. The results obtained from experiments are consistent with the calculations made by using this simple model. We concluded that the anisotropy of the intensities of N2 and O2 w...

Vibronic structure of the lowest-energy UV absorption band in cytosine

Fine vibronic structure of the lowest-energy absorption band of cytosine was obtained by low temperature UV reflectivity measurement on cytosine hydrate single crystal. The absorption spectrum was then evaluated using advanced deconvolution procedure. It has been found that the spectrum consists of successions of Frank-Condon vibronic transitions with dominating role of the breathing vibrational mode. This fact suggests remarkable increasing of interatomic distances caused by electronic excitation of cytosine molecule.

Study of γ-irradiated chloral hydrate single crystal by electron spin resonance

Electron spin resonance spectroscopy has been used to investigate γ-irradiated single crystals of chloral hydrate. The spectra are attributed to chlorine abstraction radicals and the eigenvalues and direction cosines of the g tensor are reported. It is proposed that the radical is formed by abstraction of the chlorine atom Cl 1 from the chloral hydrate molecule. It should be noted that the Cl 1 atom is also distinguished from the other chlorine atoms in nuclear quadrupole resonance investigations. Conformational changes in the molecule caused by radical formation are discussed.

Polarized phosphorescence of adeninium hemisulphate hydrate single crystal

Temperature dependence of polarized low-temperature phosphorescence spectra of single crystals of adeninium hemisulphate hydrate in the region 20–150 K was measured together with Raman spectra at temperatures 10 and 300 K. The vibronic structure of phosphorescence spectra is interpreted by means of four prevailing vibrations particularly active in Raman scattering. With increasing temperature not only the participation of individual vibrations is changed, but also the intensity of the O-O transition in phosphorescence decreases and above 150 K this transition cannot be observed at all.

Hydrogen uranyl arsenate hydrate single crystals: H 2(UO 2) 2(AsO 4) 2·8H 2O; gel growth and characterization

Single crystals of hydrogen uranyl arsenate hydrate (HUAsH) were grown in tetramethoxysilane gels at different temperatures, below and above the paraelastic-ferroelastic transition temperature, T 0. The crystals were characterized by X-ray diffraction, chemical etching, scanning electron microscopy and optical microscopy. The habit of the gel grown crystals allowed the three-dimensional features of the domain structure to be studied for the first time. A correlation was made between crystal perfection, domain structure and growth history.

The Electronic Single Crystal Spectrum of Binuclear Rhodium(II)acetate Hydrate Rh2(CH3COO)4· 2 H2O

Abstract The visible and near-ultraviolet spectrum of rhodium(II)acetate hydrate single crystals has been measured in a temperature range from 10 K to 295 K. Two band systems centered at 17,000 cm-1 and 22,000 cm-1 have been found, both consisting of components polarized parallel to and perpendicular to the rhodium-rhodium z-axis. Polarizations, intensities and temperature dependences are consistent with an assignment of z-polarized a1g →a2u and xy-polarized eg →a2u transitions for the lower energy band. For the higher energy band it could not be determined definitely whether only the b2g →-b1u and eg → b1u transitions give rise to the z-and x,y-polarization directions, respectively, or if b1g → b2u and eg →b2u also make a contribution.

ChemInform Abstract: ESR OF PARAMAGNETIC SPECIES PRODUCED BY GAMMA IRRADIATION IN CADMIUM OXALATE THREE HYDRATE SINGLE CRYSTAL

Chemischer InformationsdienstVolume 7, Issue 15 Preparative Organic Chemistry ChemInform Abstract: ESR OF PARAMAGNETIC SPECIES PRODUCED BY GAMMA IRRADIATION IN CADMIUM OXALATE THREE HYDRATE SINGLE CRYSTAL F. KOEKSAL, F. KOEKSALSearch for more papers by this authorH. YUEKSEL, H. YUEKSELSearch for more papers by this author F. KOEKSAL, F. KOEKSALSearch for more papers by this authorH. YUEKSEL, H. YUEKSELSearch for more papers by this author First published: April 13, 1976 https://doi.org/10.1002/chin.197615115AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue15April 13, 1976 RelatedInformation

ESR of Paramagnetic Species Produced by Gamma Irradiation in Cadmium Oxalate Three Hydrate Single Crystal

Paramagnetic species produced in a single crystal of cadmium oxalate three hydrate (CdC2O4 · 3H2O) by gamma irradiation have been investigated with the method of electron spin resonance. Only one radical species was observed at room temperature. Analysis of the experimental results leads to the conclusion that the species has the form RCHOH in which the unpaired electron is concentrated at the carbon atom and interacts with the two hydrogen atoms. The ESR pattern was observed nearly undiminished for more than three months after the irradiation. The g factor was found to be only very slightly anisotropic with an average value of 2.0124. The hyperfine interaction tensors of the unpaired electron with the two H nuclei have been determined.