Polarised IR and Raman spectra of monoglycine dihydrogenphosphate single crystal

Polarised Raman, IR and FIR spectra of the monoglycine dihydrogenphosphate (glycinium dihydrogenphosphate) single crystal samples are presented and discussed with respect to the crystal structure on the basis of oriented gas model approximation. The IR and FIR spectra were measured by specular reflection method and spectra of an imaginary part of the refractive indices were computed by the Kramers-Kronig transformation. The polarisation properties of the internal vibrations of the glycinium cation, H₂PO₄¹⁻ anion and hydrogen bonds are predicted and compared to the experimentally determined.     

Polarised IR and Raman spectra of the gamma-glycine single crystal

Complete (full) set of the polarised IR and Raman spectra for the gamma-glycine single crystal at room temperature are presented. The polarised IR spectra were measured by the specular reflection method and the spectra of the imaginary parts of the refractive indices were computed by Kramers-Kronig transformation. The polarised properties of the bands are discussed with respect to the normal coordinate analysis (literature data) and diffraction crystal data (oriented gas model approximation). A very good agreement between the polarised properties of the bands and simple models of vibrations are observed for the stretching vibrations of the CH2 and COO- group. It is not the case for most of the deformation vibrations of the carboxylic group and of the skeleton. The polarization properties of the stretching vibrations of the NH3+ group are determined by their hydrogen bondings.     

Polarised infrared and Raman studies of YCa4O(BO3)3 a non-linear optical single crystal

YCa4O(BO3)3-(YCOB) is a non-linear optical (NLO) material grown by Czochralski technique. Polarised IR, ATR-IR, polarised Raman and optical transmission spectral measurements were made. A series of absorption bands have been observed with intensities depending on the functional groups of the crystals. The observed bands were assigned and discussed.     

Polarised IR-microscope spectra of guanidinium hydrogensulphate single crystal

Polarised IR-microscope spectra of C(NH(2))(3)*HSO(4) small single crystal samples were measured at room temperature. The spectra are discussed on the basis of oriented gas model approximation and group theory. The stretching nuOH vibration of the hydrogen bond with the Ocdots, three dots, centeredO distance of 2.603A gives characteristic broad AB-type absorption in the IR spectra. The changes of intensity of the AB bands in function of polariser angle are described. Detailed assignments for bands derived from stretching and bending modes of sulphate anions and guanidinium cations were performed. The observed intensities of these bands in polarised infrared spectra were correlated with theoretical calculation of directional cosines of selected transition dipole moments for investigated crystal. The vibrational studies seem to be helpful in understanding of physical and chemical properties of described compound and also in design of new complexes with exactly defined behaviors.     

Polarised vibrational studies of the α-glycine single crystal: Part I. Polarised Raman spectra—the Problem of effective local Raman tensors for the glycine zwitterions

Complete (full) set of the polarised Raman spectra for the α-glycine single crystal at room temperature are presented. For the strongest bands arising from the ν_sCH₂, ν_aCH₂, δCH₂, τCH₂, νCOO⁻, δCOO and ν_sCCN vibrations effective local Raman tensors are determined applying the Tsuboi approach. The obtained results are compared to literature data available on this problem. Unfortunately, significant differences are observed between our data and other published results. This is due to the improper single crystal sample preparation for polarised Raman spectra measurements in the past. The obtained results are presented in forms which allow to apply these data for the polarised Raman spectra of other crystals of glycine compounds.     

Raman spectrum from a single crystal of SnHPO4

The polarized Raman spectrum of a single crystal of SnHPO₄ has been obtained in order to ascertain the vibrational characteristics of HPO²⁻₄ dimers in a known configuration. Bands due to hydroxyl, OH, stretching, POH bending and the hydrogen bond were observed in addition to most of the predicted lattice modes.The OH stretching mode was observed at 2730 cm⁻¹, the in-plane POH bend at 1275 cm⁻¹ and the out-of-plane POH bend at 818 cm⁻¹. A band of 55 cm⁻¹ is assigned, on the basis of its deuterium shift, to a deformation of the hydrogen bond. Very low frequency bands at 18 and 30 cm⁻¹ reflect the layer structure of SnHPO₄ in which intra-layer forces are strong and inter-layer (hydrogen bonds) forces are weak.     

Raman spectra of 3-methyl-4-nitropyridine-N-oxide single crystal

A Raman study of 3-methyl-4-nitropyridine-N-oxide single crystal (3M4NPO) has been performed at 78 K in the range 10–3500 cm⁻¹. The symmetry analysis of the vibrational modes of 3M4NPO is given. The assignments are presented for internal and external modes. The results of the Raman spectra exhibit the spectroscopic proofs of hydrogen bonds in the crystal.     

Raman spectra of single crystal Li2SeO4

The room temperature polarized Raman spectra of single crystal Li₂SeO₄ are assigned using a factor group analysis. The internal optic modes of the selenate ion are responsible for Raman bands from 920 to 440 cm⁻¹, the translational optic modes of the lithium occur in the interval from 444 to 290 cm⁻¹ and the external optic modes of the selenate ion are found between 210 and 70 cm⁻¹. The symmetry-based assignments of these bands are discussed.     

Polarised Raman and infrared spectral analysis of L-alanine oxalate (C5H9NO6)--a non-linear optical single crystal

L-alanine oxalate (C5H9NO6), a promising material for effective frequency conversion, was grown by standard slow evaporation technique. Solubility studies were carried out at different temperatures. Unambiguous assignments of fundamental modes of various molecular groups were made from the recorded infrared and polarised Raman spectra. The non-linear optical property has been confirmed from the optical transmission and fluorescence spectra.     

The Raman spectrum of hexamethylbenzene single crystal

A set of polarized Raman spectra obtained from suitable hexamethylbenzene single crystals at room temperature is presented. All the observed frequencies are attributed to intramolecular vibrations or lattice modes on the basis of clear polarization data.     

Raman intensities in Na2SO4(V) single crystal

The Raman tensors for the 9 internal vibrations of Na₂SO₄(V) (Thenardit) crystal have been computed using the Raman tensor transfer technique. The relative intensities derived from the computed tensors are in good agreement with the experimental values measured on an oriented single crystal. It means that the Raman tensors of the unperturbed sulfate groups (T_d symmetry) can be transfered to the Na₂SO₄(V) crystal (D_2h²⁴ symmetry) in the zero order approximation. Due to the particular orientation of SO₄²⁻ in the crystal, the structure of the Na₂So₄ (V) is very suitable for a illustration of the computational steps of the Raman tensor transfer technique, which have been developed here in detail.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Raman spectra and phase transitions in single crystal (NH4)2ZnCl4

Raman spectra of single crystal (NH₄)₂ZnCl₄ at 300 and 105K at different polarizations are reported and analysed in view of previously reported structural data. The experimental observations suggest that the free oriented gas model is applicable for group theoretical analysis of the vibrational modes in this system at room temperature. It is also concluded that the space group for the room temperature phase III is C²_s instead of C⁹_2v. The temperature dependence of thermosensitive bands shows discontinuities at 267 and 194 K. The structure in the new phase VI below 194 K is suggested to be triclinic.     

Polarized infrared and Raman spectra of a CsHSO4 single crystal

The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO₄ single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C_2h factor group is observed. The vibrational factor group appears to be C₂. This implies C₁ site symmetry for the SO²⁻₄ ions. The polarization features of the HSO⁻₄ ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO₃ group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance.     

The single crystal Raman spectra of Cs2Zn(N3)4

Raman spectra of Cs₂Zn(N₃)₄ are reported for single crystals at 300 K and for powdered material at 80 K, respectively. Above 200 cm⁻¹ the spectral features are dominated by the vibrational aspects of the isolated azide ions (all of which occupy general positions in the unit cell). Site group splittings have a pronounced effect in both the 600 cm⁻¹ and 1200 cm⁻¹ regions whereas in the 2000 cm⁻¹ region factor group splittings play an additional role. Infrared spectra at room temperature of powdered Cs₂Zn(N₃)₄, together with Raman and infrared spectra of K₂Zn(N₃)₄ and Rb₂Zn(N₃)₄ are also discussed.     

Raman spectra of single crystal Na2(SeO4)0.15(SO4)0.85

The room temperature polarized Raman spectra of single crystal Na₂(SeO₄)_0.15(SO₄)_0.85 are assigned, based on a factor group analysis. The internal optic modes of the oxyanions are responsible for Raman bands from 113O to 350 cm⁻¹ and the external optic modes are found between 270 and 50cm⁻¹. The symmetry-based and anion isotope abundance-based assignments of these bands are discussed.     

Monitoring the electrochemistry of single molecules by surface-enhanced Raman spectroscopy

Coherent control of chemical species in complex systems is always subject to intrinsic inhomogeneities from the environment. For example, slight chemical modifications can decisively affect transport properties of molecules on surfaces. Hence, single-molecule (SM) studies are the best solution to avoid these problems and to study diverse phenomena in biology, physics, and chemistry. Along these lines, monitoring SM redox processes has always been a "holy grail" in electrochemistry. To date, claims of SM electrochemistry by spectroscopy have come only from fluorescence quenching of polymers and redox-fluorescent molecules. In unconnected developments, the potential of the bianalyte surface-enhanced Raman scattering (SERS) method as a technique with SM sensitivity has been demonstrated. Raman spectroscopy has the potential to explore SM detection of any molecule, independent of its chemical nature. We provide definitive proof of SM events following redox cycles using SERS. The superior sensitivity and spectral richness of SERS makes it general enough to study, in principle, SM electron transfer of any (label-free) molecule.     

In situ X-ray Raman spectroscopy of LiBH4

X-Ray Raman Spectroscopy (XRS) is used to study the electronic properties of bulk lithium borohydride (LiBH(4)) and LiBH(4) in porous carbon nano-composites (LiBH(4)/C) during dehydrogenation. The lithium (Li), boron (B) and carbon (C) K-edges are studied and compared with calculations of the starting material and intermediate compounds. Comparison of the B and C K-edge XRS spectra of the as-prepared samples with rehydrogenated samples shows that the B and C electronic structure is largely regained after rehydrogenation. Both Li and C K-edge spectra show that during dehydrogenation, part of the Li intercalates into the porous carbon. This study shows that XRS in combination with calculations is a promising tool to study the electronic properties of nano-crystalline light-weight materials for energy storage.     

Towards a single crystal Raman spectrum of kaolinite at 77 K

The Raman spectra at 77 K of the hydroxyl stretching of kaolinite were obtained along the three axes perpendicular to the crystal faces. Raman bands were observed at 3616, 3658 and 3677 cm(-1) together with a distinct band observed at 3691 cm(-1) and a broad profile between 3695 and 3715 cm(-1). The band at 3616 cm(-1) is assigned to the inner hydroxyl. The bands at 3658 and 3677 cm(-1) are attributed to the out-of-phase vibrations of the inner surface hydroxyls. The Raman spectra of the in-phase vibrations of the inner-surface hydroxyl-stretching region are described in terms of transverse and longitudinal optic splitting. The band at 3691 cm(-1) is assigned to the transverse optic and the broad profile to the longitudinal optic mode. This splitting remained even at liquid nitrogen temperature. The transverse optic vibration may be curve resolved into two or three bands, which are attributed to different types of hydroxyl groups in the kaolinite.     

Optical microscopy,Raman spectroscopy,and AFM study of heavy weathered surface of barium crystal glass

Glass samples of barium crystal glass (handmade and produced by automatic technology) were weathered at controlled conditions. On the weathered glass surface, the high number of corrosion products of approximate size of (5–10) μm was found. On the unweathered (native) glass surfaces, only small non-homogeneities were observed. The micro-Raman spectroscopy was used for study of corrosion products observed by the optical microscopy. It was shown that surface roughness determined by atomic force microscopy (AFM) can be used for the quantification of degree of weathering. The stoichiometric corrosion products can be identified by Raman spectroscopy by application of the proper spectral database. The proposed method of quantification of the degree of weathering was confirmed by the coincidence of AFM results obtained for two kinds of glass samples (handmade and automatic produced) with the same chemical composition but with the different character of macroscopic surface irregularities. On the other hand, the micro-Raman spectroscopy confirmed the same chemical character of weathering process in both cases.