Region Of Internal Vibrations Research Articles

Lattice vibrations of the molecular crystal of photoreactive substance with defects

Lattice vibrations are studied theoretically by density-functional based tight-binding methods for the model structure of 2-(2'-hydroxyphenyl)benzoxazole crystal with defects. 2-(2'-hydroxyphenyl)benzoxazole is a photoreactive compound that exhibits excited state intramolecular proton transfer in the structure with an OH...N hydrogen bond. The unit cell of the model structure consists of two crystal unit cells where the molecules have the structure with intramolecular hydrogen bonds OH...N and one molecule is supposed to have a different orientation of the whole molecule or its fragment. The different orientation of the fragment forms the structure with an intramolecular hydrogen bond OH...O. It is calculated that defect caused by the different orientation of the molecule have a lower energy than the defect caused by the different orientation of the fragment. In the frequency region where the contribution of external vibrations of the molecules is significant, the vibrations mainly involve several molecules in the cell. In the region of internal vibrations there are modes, which are local vibrations of the defects. These local vibrations involve mainly motion of the atoms constituting the defect molecule. The number of local vibrations is larger for the defect that corresponds to the formation of the structure with the OH...O hydrogen bond than for the defect that corresponds to the different orientation of the whole molecule with the OH...N hydrogen bond. The internal vibrations of the defect molecule formed by the different orientation of phenol fragment in the lattice undergoes frequency shift in relation to the frequency of the modes of isolated molecule.

Experimental and theoretical study of the IR spectrum of [(CH2OH)3CNH3]2SiF6 crystal

[(CH2OH)3CNH3]2SiF6, (tris(hydroxymethyl)aminomethane)2SiF6 crystal, abbreviated as (TRIS)2SiF6 crystal, exhibits a solid–solid phase transition (PT) at 182K. The phase transition is connected with reorientational motion of SiF62− and –CH2OH groups. The vibrational infrared spectra of powdered (TRIS)2SiF6 crystal in Nujol and Fluorolube mulls were studied in the wide range of temperatures, from 320K to 133K. A wide region of internal vibrations of the TRIS+ and SiF62− ions was investigated. Temperature changes of wavenumber, width, centre of gravity, and intensity of bands were analyzed to clarify the molecular mechanism of the phase transitions. Theoretical calculations were made based on density functional theory (DFT). The calculated normal vibrational modes of the molecules, their frequencies and intensities were compared with those obtained from experimental data.

Infrared investigations of the order–disorder ferroelectric phase transitions in imidazolium halogenobismuthates(III) and halogenoantimonates(III): (C 3N 2H 5) 5Bi 2Cl 11, (C 3N 2H 5) 5Bi 2Br 11 and (C 3N 2H 5) 5Sb 2Br 11

Infrared spectra of the powdered (C 3N 2H 5) 5Bi 2Cl 11, (C 3N 2H 5) 5Bi 2Br 11and (C 3N 2H 5) 5Sb 2Br 11 crystals in the region of internal vibrations of the imidazolium cations (3600 and 400 cm −1) at the temperature intervals of 10–300 K, covering paraelectric–ferroelectric phase transitions, are presented and discussed in this paper. The research shows that the vibrational states of the imidazolium cations change markedly during the paraelectric–ferroelectric phase transition. The continuous nature of these transitions is well reflected in the infrared spectra, which is consistent with the previous X-ray and dielectric findings.

Properties of (NH 4) 2SbF 5 crystal: Infrared and thermal studies

Phase transitions of ammonium pentafluoroantimonate (NH 4) 2SbF 5 crystal have been investigated by thermal and infrared measurements. Differential scanning calorimetry showed two phase transitions: at 291 K and about 171 K. This result is similar to the issues obtained during specific heat investigations. The infrared spectra of powdered (NH 4) 2SbF 5 crystal in Nujol and Perfluorolube oil were studied in the wide region of internal vibration of the NH 4 + and SbF 5 2 − ions (6000–400 cm −1) in the temperature range between 98 and 320 K. The temperature changes of wavenumber, half-width, center of gravity and intensity of the bands were analysed to clarify the cationic and anionic dynamics contribution to the phase transitions mechanisms. The separate bands were assigned to vibrations of two inequivalent ammonium ions below 168 K.

2,4,6-Triamino-1,3,5-triazin-1-ium Acetate Acetic Acid Solvate Monohydrate. Infrared and Raman Spectra

The crystals of the new melaminium salt, i.e. melaminium acetate acetic acid solvate monohydrate, C 3 H 7 N 6 +.CH 3 COO - .CH 3 COOH.H 2 O, were obtained by the slow evaporation of an aqueous solution at room temperature. Powder infrared and Raman spectra were measured and interpreted. The vibrational spectra in the region of internal vibrations of ions corroborate structural data recently published by Perpetuo and Janczak. 1 Some spectral features of this new crystal are referred to corresponding one for melamine crystal as well as other melamine complexes in crystalline form. Hydrogen-bonded network present in the crystal gives notable vibrational effect.

Structure and spectra of melaminium citrate

The first X-ray diffraction and vibrational spectroscopic analysis of the new melaminium salt, i.e. melaminium citrate, C 3H 7N 6 +·C 6H 7O 7 −, has been reported. Crystals were obtained by slow evaporation of an aqueous solution at room temperature. Powder infrared and Raman spectra were measured and interpreted. The vibrational spectra in the region of internal vibrations of ions corroborate structural data. Some spectral features of this new crystal are referred to the corresponding one for melamine crystal as well as other melamine complexes in crystalline form. Hydrogen-bonded network present in the crystal gives notable vibrational effect. No anomaly was detected in the heat-flow vs. temperature diagram in the range of 320–100 K.

Polarised infrared and Raman studies of K 4LiH 3(SO 4) 4 single crystal : Part 1. Room temperature experiments

Room temperature polarised infrared and Raman measurements for the tetrapotassium lithium trihydrogentetrasulphate(VI) (K 4LiH 3(SO 4) 4) single crystal were carried out. The stretching vibration of the short (2.500 Å) asymmetric hydrogen bond gives rise to the strong and broad absorption in the range of 1500–400 cm −1 in the spectra polarised in the c-direction. The band corresponding to the out-of-plane bending type of vibration appears at 1004 cm −1 and is not observed in Raman spectra. The long (2.547 and 2.532 Å) hydrogen bonds give rise to an ABC structure. The vibrational spectra in the region of internal vibrations of sulphate corroborate the X-ray diffraction data. Some spectral features of K 4LiH 3(SO 4) 4 (K 4LiD 3(SO 4) 4) are referred to corresponding one for Rb 4LiH 3(SO 4) 4 (Rb 4LiD 3(SO 4) 4) and K 4LiH 3(SeO 4) 4 (K 4LiD 3(SeO 4) 4).

Infrared and Raman spectra of the new melaminium salt: 2,4,6-triamino-1,3,5-triazin-1-ium hydrogenphthalate

Room temperature powder infrared and Raman measurements for the new melaminium salt, 2,4,6-triamino-1,3,5-triazine-1-ium hydrogenphthalate, C 3H 7N 6 +·C 8H 5O 4 − were carried out. In the region of internal vibrations of ions, the vibrational spectra corroborate the X-ray data published recently. Some spectral features of this new crystal are referred to be corresponding both to melamine crystal and other melamine complexes in crystalline form. Intense hydrogen-bonded network is present in the crystal structure of the complex with noticeable vibrational effects. DSC measurements do not indicate any phase transition in the temperature range 113–293 K.

Infrared and Raman Spectra of Bis(Melaminium) Sulfate Dihydrate

Room temperature powder infrared and Raman measurements for the new melaminium salt, bis(2,4,6-triamino-1,3,5-triazin-1-ium) sulfate dihydrate, 2C3H7N6+·SO42-·2H2O, in the crystalline state, were carried out. The vibrational spectra in the region of internal vibrations of the ions corroborate recent X-ray data of Janczak et al. Some spectral features of this new crystal are referred to those of other crystalline melaminium salts.

Structure, spectra and phase transition in p-nitroanilinium perchlorate crystal

The first X-ray diffraction and vibrational spectroscopic analysis of a novel complex between p-nitroaniline and perchloric acid is reported. The structure was solved in 295 K. Room temperature powder infrared and Raman measurements for the p-nitroanilinium perchlorate (1:1) crystals were carried out. The vibrational spectra in the region of internal vibrations of ions corroborates the X-ray data which show that p-nitroaniline molecule is monoprotonated. DSC measurements on powder sample indicate the phase transition point at about 213 and 208 K for heating and cooling, respectively. No detectable signal was observed during powder test for second harmonic generation.

Infrared and Raman spectra of melaminium chloride hemihydrate

Room temperature powder infrared and Raman measurements for the new melaminium salt, 2,4,6-triamino-l,3,5-triazine-1-ium chloride hemihydrate, C 3H 8N 6 +·Cl − · 0.5H 2O were carried out. The vibrational spectra in the region of internal vibrations of ions corroborates the X-ray data recently published by Janczak (Acta Crystallogr. 57 (2001) 1120) Some spectral features of this new crystal are referred to corresponding one for melamine crystal as well as other melamine complexes in crystalline form.

A molecular dynamics simulation of the vibrational properties of the Ar1−x(N2)x crystal

A classical molecular dynamics calculation of the vibrational properties (and in particular of the infrared and Raman response) of the Ar1−x(N2)x mixed crystal is presented based on an intermolecular interaction potential including electrostatic terms. The lattice and internal vibration region are discussed separately. The vibrational properties are correlated with the structural properties and with the orientational ordering in the crystals.

Raman spectroscopic study of phase transformation in single crystals of cadmium fluorosilicate hexahydrate

AbstractA detailed temperature‐dependent Raman study of oriented single crystals of CdSiF6 · 6H2O down to 10 K was made in the region of internal vibrations and lattice modes. The frequency shifts, Iinewidths and intensities of some of the modes associated with the [Cd(OH2)6]2+ and (SiF6)2− ions show abrupt changes at temperatures around 220 K and some doubly degenerate modes split into two components. These studies suggest that the system undergoes a structural phase transition at ca. 220 K.

Laser Raman study of single crystals of deuterated cadmium fluorosilicate

A laser Raman study of oriented single crystals of CdSiF 6:6D 2O at room temperature as well as at 10 K in all the six polarization geometries has been made. Also a detailed temperature dependent Raman study from room temperature to 10 K in ( yy) polarization in the region of internal vibrations and lattice modes has been made. Abrupt changes have been observed in frequency shift, line-width and intensity of some of the bands at about 235 K. Some doubly degenerate modes show splitting at the same temperature. From these observations a phase change at about 235 K is inferred for this salt. It has been suggested that when the system is cooled, the lattice contracts and the water molecules lose their reorientational freedom to some extent which might result in the distortion of the [Cd(OD 2) 6] 2+ octahedra triggering a phase transition.

Spectroscopic Studies of Photochemical Reactions in Organic Solids. Photodimerization of p-Formylcinnamic Acid

Abstract Raman phonon spectroscopy and electronic absorption and emission spectroscopy have been used to study the mechanism of reaction and the role of electron–phonon coupling in determining the photoreactivity of p-formylcinnamic acid (p-FCA) in the crystalline state. Raman and infrared spectroscopy in the internal vibration region have been used to characterize the reactant p-FCA and the dimeric product t-3,t-4-bis(p-formylphenyl)-ν-1,c-2-cyclobutanedicarboxylic acid. Phonon spectroscopy reveals that the reaction proceeds principally by a heterogeneous mechanism though a homogeneous mechanism in the initial stage of short time domain can not be ruled out. The electronic spectroscopy suggests a strong electron–phonon coupling in the monomer crystal.

Effet de la Temperature sur les Modes Externes de Vibration du Monocristal. La2(SO4)3·9(H,D)2O

AbstractThe polarized Raman spectra in the region 0–400 cm−1 of oriented single crystals of La2(SO4)3.9H2O and La2(SO4)3. 9D2O have been recorded between 14 and 297 K. The behaviour of the external modes is analysed in order to elucidate the role of the hydrogen‐bonds and the lanthanum‐oxygen interactions in the order‐disorder transition observed at approximately 170 K. Large changes in the shape and intensities of the external bands with temperature (not detected in the region of internal vibration of the spectrum) have been observed.

ChemInform Abstract: RAMAN SCATTERING AND PHASE TRANSITION OF AMMONIUM NITRATES

AbstractDie polarisierten Raman‐Spektren von Einkristallen der Raumtemp.‐Phase NH4NO3 (IV) lassen sich im Bereich der niederfrequenten Gitterschwingungen und im Bereich der inneren Schwin gungen auf der Grundlage der D?l‐Struktur interpretieren.

Raman Scattering and Phase Transition of Ammonium Nitrates

Abstract Polarized Raman spectra of single crystals are observed for the room-temperature phase NH4NO3(IV). The spectra in the low-frequency lattice vibration region as well as in the internal vibration region are well interpreted based on D2h13 structure. Raman spectra of powdered samples are measured at various temperatures covering whole phases NH4NO3 I–V. A characteristic feature of Raman spectrum is clarified for each phase. An abrupt spectral change occurs in the phase transition, indicating a first order transition. The splitting of Ag and B1g components of ν3 (asymmetric stretching mode of NO3− ion) in NH4NO3 is quite large, due to the strong interionic interaction between NH4+ and NO3− ions.

Bound and many-particle states in polariton Raman spectra of NH 4Cl crystals

The properties of polariton Raman spectra for the internal vibration region of NH 4Cl crystal are discussed. These spectra have been recorded by means of a copper laser ( λ = 5105 and 5782 A ̊ ) for sample temperature T=80 and 10°K. According to the theory a polariton singularities in the region of a polar bound state has been obtained. The two-particle bands have been studied and a very complicate structure inside of these bands has been revealed. Moreover, multiphonon singularities at polariton curves have been observed. The experimental polariton law has been compared to the theory and a conclusion has been made as to the necessity of a further development of the theory.

Intermolecular interaction and infra-red spectra of the three crystalline phases of potassium nitrate—I. Internal vibration region

A polarized infra-red absorption of monocrystalline KNO 3 samples has been studied in the region of nitrate ion internal vibrations at temperatures 90–575°K. The vibration resonance interactions observed in KNO 3-II are in agreement with the conception of local and correlational field effect. Some peculiarities in the spectrum of KNO 3-I were interpreted as arising from orientational disorder of nitrate ions in the (001) plane.