A vibrational spectroscopic study of perhamite, an unusual silico-phosphate

The silico-phosphate mineral perhamite has been studied using a combination of electron and vibrational spectroscopy. SEM photomicrographs reveal that perhamite morphology consists of very thin intergrown platelets that can form a variety of habits. Infrared spectroscopy in the hydroxyl-stretching region shows a number of overlapping bands which are observed in the range 3581-3078 cm(-1). These wavenumbers enable an estimation to be made of the hydrogen bond distances in perhamite: 3.176(0), 2.880(5), 2.779(6), 2.749(3), 2.668(1) and 2.599(7)A. Intense Raman bands are observed in the region 1110-1130 and 966-996 cm(-1) and are assigned to the SiO(4) and PO(4) symmetric stretching modes. Other bands are observed in the range 1005-1096 cm(-1) and are attributed to the nu(3) antisymmetric bending modes of PO(4). Some low intensity bands around 874 cm(-1) were discovered and remain unclassified. Bands in the low-wavenumber region are assigned to the nu(4) and nu(2) out-of-plane bending modes of the OSiO and PO(4) units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multi-anion minerals such as perhamite. Information on such a mineral would be difficult to obtain by other means.     

Synthetic deuterated erythrite--a vibrational spectroscopic study

A comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm(-1). The band at 3442 cm(-1) is attributed to weakly hydrogen bonded water and the band at 3039 cm(-1) to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm(-1). The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm(-1). Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm(-1) and new bands are observed at 692, 648 and 617 cm(-1). These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm(-1) with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers.     

Synthesis, NMR and vibrational spectroscopic characterization, and computational study of the cis-IO2F3 2- anion

The N(CH3)4(+) salt of the cis-IO2F3(2-) anion was synthesized from [N(CH 3)4][IO2F2] and excess [N(CH3)4][F] in CH3CN solvent. The [N(CH3)4] 2[IO2F3] salt was characterized by Raman, infrared, and (19)F solid-state MAS NMR spectroscopy. Geometry optimization and calculation of the vibrational frequencies at the DFT level of theory corroborated the experimental finding that the IO2F3(2-) anion exists as a single isomer with a cis-dioxo and mer-trifluoro arrangement. The fluorine atom in IO2F3(2-) that is trans to one of the oxygen atoms is weakly bound with a calculated bond length of 228.1 pm. The IO2F3(2-) anion is only the second example of an AEO 2F 3 species after XeO2F3(-).     

Raman spectroscopic study of mixed carbonate materials

The main parameters for precipitation of mixed carbonate materials have been studied by Raman microscopy. These carbonates are compounds of barium, strontium and calcium. It has been shown that the Raman spectrum of a sample is exclusively controlled by its composition, the precipitation parameters do not affect the crystal structure. Even at relatively low levels, the calcium content of a sample can dominate the vibrational frequencies as measured by Raman spectroscopy. Calcium contents greater than 17% show this effect to a considerable degree, and give the broadest or two Raman peaks and thus the least uniform unit cells. The analysis of the lattice modes demonstrates that each Raman shift observed for a mixed carbonate sample corresponds to a specific crystal structure. Some peaks lie within two or three shifts that are observed for different crystal structures.     

Organotin(IV) azido and mixed azidothiocyanato complex anions; A Mössbauer and vibrational spectroscopic study

Tetraphenylarsonium and tetramethylammonium salts of the complex anions Ph₃Sn(N₃)^?₂, Ph₃Sn(N₃)(NCS)^?, Me₂Sn(N₃)^2?₄ and Ph₂Sn(N₃)₂(NCS)^2?₂ have been synthesized, and the solid state configuration of the complex anions has been studied by Mössbauer and vibrational spectroscopies. Trigonal bipyramidal structures are advanced for the Ph₃Sn^IV derivatives, with equatorial SnC₃ and apical pseudohalide ligands, while the R₂Sn^IV compounds are assumed to be trans-octahedral species. The NCS^? ligands are observed to be N-bonded to Sn^IV. Conductance and PMR (for the Me₂Sn^IV compound) data suggest the presence of the complex anions also in solution phases.     

A spectroscopic study of some radio frequency mixed gas plasmas

A spectroscopic study of some radio frequency argon-methane, sulphur, phosphorus and halogen plasmas has been carried out. Their analytical utility was assessed and some temperature measurements in the argon-methane plasma carried out. A number of novel lines is reported in the argon-sulphur plasma spectrum and an excitation process in these plasmas discussed.     

Molecular structure of bismuth trichloride from combined electron diffraction and vibrational spectroscopic study

The results of an electron diffraction reanalysis, augmented with a combined electron diffraction and vibrational spectroscopic elucidation, of the molecular structure of BiCl₃ are reported. The principal parameters arer _g (Bi-Cl)=2.424±0.005 å (r =2.417±0.005 å) and <Cl-Bi-Cl=97.5±0.2. They are in excellent agreement with previous electron diffraction analysis [1], utilizing a more limited data range from the same experiment. They are also fully consistent with the expected trends of geometrical variation in the Group V trihalide series. The force fields of BiCl₃, determined by normal coordinate analysis and by combined analysis, agree within experimental error.     

Deviation from the planarity--a large Dy3N cluster encapsulated in an Ih-C80 cage: an X-ray crystallographic and vibrational spectroscopic study

The high-yield synthesis of Dy3N@C80 (I) opens the possibility of characterizing its molecular and vibrational structures. We report on the structure determination of Dy3N@C80 (I) by X-ray crystallographic study of single crystal of Dy3N@C80.Ni(OEP).2C6H6, revealing a nearly planar Dy3N cluster encapsulated in an Ih-C80 cage. The vibrational structure of Dy3N@C80 (I) is studied by Fourier transform infrared (FTIR) and Raman spectroscopy in combination with force-field calculations. A correlation was found between the antisymmetric metal-nitrogen stretching vibration and the structure of the M3N cluster of M3N@C80 (I) (M = Y, Gd, Tb, Dy, Ho, Er, Tm). Moreover, a stronger interaction between the encaged nitride cluster and the C80 carbon cage was found in the class II M3N@C80 (I) (M = Y, Gd, Tb, Dy, Ho, Er, Tm) than in Sc3N@C80 (I). This study demonstrates that the cluster size plays the dominating role in the structure of the M3N cluster in M3N@C80 (I).     

Rietveld refinement and vibrational spectroscopic study of alunite from el Gnater, central Tunisia

The crystal structure of alunite (K_0.72,Na_0.28) Al₃(SO₄)₂(OH)₆ from El Gnater, central Tunisia, is refined by the Rietveld method. Raman and infrared data of this mineral are also given in order to provide some further information about the mineralogy and chemistry of this alunite. The crystal system is trigonal, space group R $ \bar 3 The crystal structure of alunite (K_0.72,Na_0.28) Al₃(SO₄)₂(OH)₆ from El Gnater, central Tunisia, is refined by the Rietveld method. Raman and infrared data of this mineral are also given in order to provide some further information about the mineralogy and chemistry of this alunite. The crystal system is trigonal, space group R m, with a = 6.9834(4) ? and c = 17.0899(11) ?. Final Rietveld refinement converges to R _p = 0.16, R _wp = 0.16, and R _Bragg = 0.07. In the alkalic site, the occupancy of potassium and sodium is refined to 72 and 28%, respectively. The Raman and infrared spectra are investigated in order to improve previous assignments of the observed frequencies, especially for tetrahedral and octahedral vibration and OH group, which are discussed on the basis of unit-cell group analysis and by comparison with previously observed wavenumbers of natrojarosite and synthetic alunite. The text was submitted by the authors in English.     

Picosecond IR-UV pump-probe spectroscopic study on the vibrational energy flow in isolated molecules and clusters

Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) from the XH stretching vibrations, where X refers to O or C atom, of aromatic molecules and their hydrogen(H)-bonded clusters are investigated by picosecond time-resolved IR-UV pump probe spectroscopy in a supersonic beam. For bare molecules, we mainly focus on IVR of the OH stretch of phenol. We describe the IVR of the OH stretch by a two-step tier model and examine the effect of the anharmonic coupling strength and the density of states on IVR rate and mechanism by using isotope substitution. In the H-bonded clusters of phenol, we show that the relaxation of the OH stretching vibration can be described by a stepwise process and then discuss which process is sensitive to the H-bonding strength. We discuss the difference/similarity of IVR/VP between the "donor" and the "acceptor" sites in phenol-ethylene cluster by exciting the CH stretch vibrations. Finally, we study the vibrational energy transfer in the isolated molecules having the alkyl chain, namely phenylalcanol (PA). In this system, we measure the rate constant of the vibrational energy transfer between the OH stretch and the vibrations of benzene ring which are connected at the both ends of the alkyl chain. This energy transfer can be called "through-bond IVR". We investigate the three factors which are thought to control the energy transfer rate; (1) "OH <--> next CH(2)" coupling, (2) chain length and (3) conformation. We discuss the energy transfer mechanism in PAs by examining these factors.     

Infrared spectroscopic study of mixed copper-cobalt and copper-nickel formate dihydrates (cation distribution in mixed crystals).

The infrared (IR) spectra of Co(HCOO)2 x 2H2O, Ni(HCOO)2 x 2H2O and Cu2Co(Ni)1-x (HCOO)2 x 2H2O mixed crystals (0 < x < or = 0.5) have been recorded and the internal modes of the formate groups and the water molecules are discussed. The analysis of the spectra of the mixed crystals reveals that when copper ions replace cobalt and nickel ions in Co(HCOO) x 2H2O and Ni(HCOO)2 x 2H2O, the Cu2+ ions are localized at the two available positions. However, the occupancy degree of the Me(1) and Me(2) sites by the different cations needs X-ray diffraction (XRD) studies of the single crystals. The new crystal phase Co0.17Cu0.83(HCOO)2 x 2H2O obtained from the Co(HCOO)2 x 2H2O-Cu(HCOO)2 x 2H2O-H2O system at 50 degrees C crystallizes in the monoclinic system with lattice parameters: a = 12.329(4); b = 7.241(2); c = 8.707(5) A and beta = 103.13(3) degrees (SG probably P2/c). The number of the bands corresponding to the uncoupled OD vibrations and the water librations shows that probably more than two water molecules are expected to exist in the structure. Furthermore, it is assumed that the water molecules bonded to the copper ions form stronger hydrogen bonds (stronger Cu-OH2 interaction) than those bonded to the cobalt ions.     

Comparative vibrational spectroscopic study of 1,3-diacetylbenzene and 2,6-diacetylpyridine aided with density functional calculation

Comparative studies of the Raman and infrared spectra of 1,3-diacetylbenzene and 2,6-diacetylpyridine have been made. The spectra are interpreted with the aid of normal mode analysis following full structure optimization based on the density functional method using different levels of theories and various basis sets combination. The unscaled DFT LSDA frequencies approximate the experimental ones in much more uniform fashion than B3LYP or B3PW91 theories do. Nevertheless the use of overall scale factor leads to further significant improvement with less than 2% error. The scaled B3PW91 6-31G result is best, even though LSDA 6-311G frequencies are superior to the B3PW91 ones before scaling. While making complete assignments of vibrational wavenumbers on the basis of potential energy distribution, some interesting observation in the vibrational spectra of these two molecules have been noticed. Instances of Fermi resonances between fundamentals and some combination modes of vibration have also been ascertained. Following the quantum chemical calculation optimized geometries of the both molecules are predicted. The theoretical global minimum energy calculation helps to find the structural symmetries of the molecules.     

Synthesis and vibrational spectroscopic characterisation of nickel containing aurichalcite

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise a synthetic nickel substituted aurichalcite a zinc/nickel hydroxy carbonate, (Zn²⁺, Cu²⁺, Ni²⁺)₅(CO₃)₂(OH)₆. XRD patterns show high orientation and indicate the presence of some minor impurities. The diffraction patterns for the Ni-aurichalcite are well correlated with the standard reference patterns. EDAX analyses indicate variations in chemical composition of Zn/Ni ratios of ∼20:1. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band for the Ni-aurichalcite at 1070 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for Ni-aurichalcite at 1372, 1480 and 1543 cm⁻¹. Multiple Raman bands are observed in the regions from 800 to 850 cm⁻¹ and 720 to 750 cm⁻¹, and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. This research proves that nickel containing aurichalcites can be synthesised in the laboratory thus mimicing the natural nickel containing aurichalcites.     

Conformational analysis and vibrational spectroscopic investigation of 3-phenylpropylamine

The possible stable forms of 3-phenylpropylamine (3-PPA) molecule were experimentally and theoretically studied by infrared and Raman spectroscopy. FT-IR and Raman spectra of 3-PPA were recorded in the regions of 4000–400 cm⁻¹ and 3700–60 cm⁻¹, respectively. The potential energy surface corresponding to the internal rotations of the molecule was investigated by semi-empirical quantum mechanical methods, and appropriate conformers defined with B3LYP hybrid density functional theory method along with the basis sets of different size and type. Results from experimental and theoretical data showed the trans–trans–gauche (TTG) to be the most stable form of a 3-PPA molecule.     

A study of the anion mobility in mixed fluorides with the tysonite structure

Summary From the studies which have been carried out it follows that in Berthollide solid solutions with the tysonite structure there is intensive diffusion of fluoride ions in the vacancies, and this is responsible for the electrical conductivity of the crystals. It follows from an analysis of the NMR data obtained that the fluorine vacancies are produced in the positions corresponding to fluorine atoms of low mobility, confirming structural studies which indicate the preferential formation of vacancies in the F_III positions. At low temperatures, the movement of the highly mobile F_I fluorine atoms shows practically no association with the low-mobility F_III positions. Thus in spite of the high concentration of anion vacancies in the specimens studied, the mobility of fluorine at low temperatures does not increase, compared with the ideal tysonite structure. It follows from the temperature dependence of the¹⁹F NMR spectra, however, that the presence of vacancies increases the mobility in the subsystems of fluorine atoms with low mobility and increases the exchange between the fluorine atoms with high and low mobilities.L. V. Kirenskii Institute of Physics, Siberian Branch, Academy of Sciences of the USSR. Institute of Crystallography, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 20, No. 4, pp. 622–626, July–August, 1979.     

Solid-state vibrational spectroscopy: Part 11. An infrared and raman vibrational spectroscopic study of metal(II) halide aniline complexes

Infrared (4000?200 cm^?1) and Raman (3500?50 cm^?1) spectra are reported for metal(II) halide aniline complexes of the following stoichiometries: (MX₂an₂) (M  Co, Ni or Hg, X  Cl; M  Mn, X  Cl or Br; M  Zn or Cd, X  Cl, Br or I); (MX₂an₃) (M  Mn, X  Cl or Br; M  Ni, X  Cl); (CdCl₂an) and an assignment is proposed for all the observed bands. Low-temperature (83 K) IR spectra are also reported and it is noted that whilst the aniline ring and CH mode values are virtually insensitive to temperature, the NH₂ rocking and metal-ligand stretching mode values increase with decreasing temperature, whilst the NH₂ stretching mode values decrease with decreasing temperature.     

Hydrogen-bonding between pyrimidine and water: a vibrational spectroscopic analysis

We present an experimental and a theoretical study on hydrogen-bonding between pyrimidine and water as the H-donor. The degree of hydrogen-bonding in this binary system varies with mixture composition. This was monitored experimentally by polarization-resolved linear Raman spectroscopy with the pyrimidine ring breathing mode nu1 as a marker band. A subsequent quantitative line shape analysis of the isotropic Raman intensity for 24 pyrimidine/water mixtures clearly revealed a splitting into three spectral components upon dilution with water. The two additional peaks have been assigned to distinct groups of hydrogen-bonded species that differ in the number of pyrimidine nitrogen atoms (N) involved in hydrogen-bonding to water hydrogen atoms (H). From the integrated Raman intensities for "free" and "hydrogen-bonded" pyrimidine, a concentration profile for these species was established. Our assignments and interpretations are supported by quantum mechanical calculations of structures and by vibrational spectra for pyrimidine and 10 pyrimidine/water complexes with increasing water content. Also, accurate structure-spectra correlations for different cluster subgroups have been determined; within each particular cluster subgroup the water content varies, and a perfect negative correlation between NH hydrogen-bond distances and nu1 wavenumbers was observed.     

A vibrational spectroscopic study of structure evolution of water dissolved in supercritical carbon dioxide under isobaric heating

A combination of Raman scattering spectroscopy and infrared absorption was applied to investigate the structural evolution of water dissolved in supercritical carbon dioxide under isobaric heating (T=40-340 degrees C, P=250 bar). Quantitative analysis of experimental spectra allowed us to determine that at relatively moderate temperatures water dissolved in CO(2)-rich phase exists only under monomeric form (solitary water surrounding by CO(2) molecules), but hydrogen-bonded species, namely, dimers, begin to appear upon heating. At the same time, the ratio of dimers to monomers concentration increases with further temperature increase and at temperatures close to the temperature of total miscibility of the mixture (T=366 degrees C, P=250 bar), water dimers only are present in the CO(2)-rich phase.     

C78 cage isomerism defined by trimetallic nitride cluster size: a computational and vibrational spectroscopic study

Molecular structures of Dy(3)N@C(78) and Tm(3)N@C(78) clusterfullerenes are addressed by the IR and Raman vibrational spectroscopic studies and density functional theory (DFT) computations. First, extensive semiempirical calculations of 2927 isomers of C(78) hexaanions followed by DFT optimization were applied to establish their relative stability. Then, DFT calculations of a series of M(3)N@C(78) (M = Sc, Y, Lu, La) isomers were performed which have shown that the stability order of the isomers depends on the cluster size. While the Sc(3)N cluster is planar in the earlier reported Sc(3)N@C(78) (D(3)h: 24,109) clusterfullerenes, relatively large Y(3)N and Lu(3)N clusters would be forced to be pyramidal inside this cage, which would result in their destabilization. Instead, these clusters remain planar in the nonisolated pentagon rule (non-IPR) C(2): 22,010 isomer making Y(3)N@C(78) and Lu(3)N@C(78) clusterfullerenes with this cage structure the most stable ones. Finally, on the basis of a detailed analysis of their IR and Raman spectra supplemented with DFT vibrational calculations, the recently isolated Tm(3)N@C(78) and the major isomer of Dy(3)N@C(78) are assigned to the non-IPR C(2): 22,010 cage structure. A detailed assignment of their experimental and computed IR and Raman spectra is provided to support this conclusion and to exclude other cage isomers.     

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO–LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.