Ν4 Regions Research Articles

Analysis and modeling of combination bands of sulfur hexafluoride 32SF6 based on global fits. Update of the SHeCaSDa database

Sulfur hexafluoride is a powerful greenhouse gas of industrial origin. Remote-sensing detection of this heavy species requires a detailed knowledge of its infrared absorption spectra that features many hot bands at room temperature. It is thus necessary to study many of its rovibrational levels which are implied in such hot band transitions. Based on our previous results reporting global fits of many rovibrational bands (Faye et al., 2017), we present here detailed analyses of three combination bands, namely ν1+ν4,ν2+ν6 and ν5+ν6. The ν2+ν6 combination band has been already investigated some years ago, but the present analysis represents a strong improvement; the two other bands are analyzed in detail for the first time. The results contribute to improve the simulation of hot bands in the strongly absorbing ν3 and ν4 regions and they have been used to update the SHeCaSDa database (http://vamdc.icb.cnrs.fr/PHP/shecasda.php).

Vibrational spectra of the rare‐occurring complex hydrogen arsenate minerals pharmacolite, picropharmacolite, and vladimirite: Dominance of Raman over IR spectroscopy to discriminate arsenate and hydrogen arsenate units

AbstractThis work represents the first complete experimental and theoretical study of the infrared (IR) spectra of pharmacolite, Ca(AsO3OH)·2H2O; vladimirite, Ca4(AsO3OH)(AsO4)2·4H2O; and picropharmacolite, Ca4Mg(AsO3OH)2(AsO4)2·11H2O. IR spectra, collected at both room and liquid nitrogen temperature, have shown similar spectral view among minerals in the region of ν1 to ν4 modes, surprisingly not involving complexity in vladimirite and picropharmacolite spectral view due to the presence of both AsO3OH and AsO4 units compared to pharmacolite where only AsO3OH units appear in the structure. On the other hand, vladimirite and picropharmacolite Raman spectra in the corresponding ν1 to ν4 region (955–350 cm−1) exhibit existence of 3 sets of 2 bands (6 in total) completely reflecting the existence of 3 symmetrically nonequivalent AsO4 groups in the structures of vladimirite and picropharmacolite (of which one is protonated) and only one set of ν1 to ν4 bands from the structurally equivalent AsO3OH units in the pharmacolite structure. The liquid nitrogen temperature IR spectra enabled to infer important information regarding the OH vibrational bands related to the AsO3OH groups and to the water molecules. Essentially, all bands in the vibrational spectra were assigned and correlated with the findings for a plethora of structurally similar complex hydrogen arsenate minerals. To support the tentative assignment of bands in the vibrational spectra, quantum theoretical calculations were performed within the framework of density functional theory. On the basis of theoretical calculations, a few reassignments of bands appearing in the OH stretching region are proposed. X‐ray powder diffraction was used to confirm authenticity of the title systems.

Raman and infrared spectroscopic study of kamphaugite-(Y)

We have studied the carbonate mineral kamphaugite-(Y)(CaY(CO3)2(OH)·H2O), a mineral which contains yttrium and specific rare earth elements. Chemical analysis shows the presence of Ca, Y and C. Back scattering SEM appears to indicate a single pure phase. The vibrational spectroscopy of kamphaugite-(Y) was obtained using a combination of Raman and infrared spectroscopy. Two distinct Raman bands observed at 1078 and 1088cm−1 provide evidence for the non-equivalence of the carbonate anion in the kamphaugite-(Y) structure. Such a concept is supported by the number of bands assigned to the carbonate antisymmetric stretching mode. Multiple bands in the ν4 region offers further support for the non-equivalence of carbonate anions in the structure. Vibrational spectroscopy enables aspects of the structure of the mineral kamphaugite-(Y) to be assessed.

Infrared spectroscopic study of SO42− ions included in M′2M′′(SeO4)2⋅6H2O (Me′ = K, NH4+; M′′ = Mg, Co, Ni, Cu, Zn) and NH4+ ions included in K2M(XO4)2⋅6H2O (X = S, Se; M′′ = Mg, Co, Ni, Cu, Zn)

Infrared spectra of Tutton compounds, M′2M′′(XO4)2⋅6H2O (M′=K, NH4+; M′′=Mg, Co, Ni, Cu, Zn; X=S, Se), as well as those of SO42− guest ions included in selenate host lattices and of NH4+ guest ions included in potassium host lattices are presented and discussed in the regions of ν3 and ν1 of SO42− guest ions, ν4 of NH4+ guest ions and water librations.The SO42− guest ions matrix-isolated in selenate matrices (approximately 2mol%) exhibit three bands corresponding to ν3 and one band corresponding to ν1 in good agreement with the low site symmetry C1 of the host selenate ions. When the larger SeO42− ions are replaced by the smaller SO42− ions the mean values of the asymmetric stretching modes ν¯3 of the included SO42− ions are slightly shifted to lower frequencies as compared to those of the same ions in the neat sulfate compounds due to the smaller repulsion potential of the selenate matrices (larger unit-cell volumes of the selenates). It has been established that the extent of energetic distortion of the sulfate ions matrix-isolated in the ammonium selenates as deduced from the values of Δν3 and Δν3/νc is stronger than that of the same ions matrix-isolated in the potassium selenates due to the formation of hydrogen bonds between the SO42− guest ions with both the water molecules in the host compounds and the NH4+ host ions (for example, Δν3 of the sulfate guest ions have values of 30 and 51cm−1 in the nickel potassium and ammonium compounds, and 33 and 49cm−1 in the zinc potassium and ammonium compounds, respectively).The infrared spectra of ammonium doped potassium sulfate matrices show three bands corresponding to Δν4 of the included ammonium ions in agreement with the low site symmetry C1 of the host potassium ions. However, the inclusion of ammonium ions in selenate matrices (with exception of the magnesium compound) leads to the appearance of four bands in the region of ν4. At that stage of our knowledge we assume that some kind of disorder of the ammonium ions included in selenate lattices occurs due to the different proton acceptor capability of the SO42− and SeO42− ions. The latter ions are known to exhibit stronger proton acceptor abilities. This fact will facilitate the formation of polyfurcate hydrogen bonds of the ammonium ions in the selenate matrices, thus leading to increasing in the coordination number of these ions, i.e. to a disorder of the ammonium guest ions.The strength of the hydrogen bonds formed in the title Tutton compounds as well as that of the hydrogen bonds in potassium compounds containing isomorphously included ammonium ions as deduced from the wavenumbers of the water librations are also discussed. The bands corresponding to water librations in the spectra of the mixed crystals K1.8(NH4)0.2M(XO4)2⋅6H2O (M=Mg, Co, Ni, Cu, Zn; X=S, Se) broaden and shift to lower frequencies as compared to those of the potassium host compounds, thus indicating that weaker hydrogen bonds are formed in the mixed crystals. These spectroscopic findings are owing to the decrease in the proton acceptor capacity of the SO42− and SeO42− ions due to the formation of hydrogen bonds between the host anions and the guest ammonium cations additionally to water molecules (anti-cooperative or proton acceptor competitive effect). Furthermore, the band shifts in the spectra of the selenate matrices are generally larger than those observed in the spectra of the respective sulfates due to the stronger proton acceptor ability of the selenate ions.

The molecular structure of the vanadate mineral mottramite [PbCu(VO4)(OH)] from Tsumeb, Namibia – A vibrational spectroscopic study

We have studied a mineral sample of mottramite PbCu(VO4)(OH) from Tsumeb, Namibia using a combination of scanning electron microscopy with EDX, Raman and infrared spectroscopy. Chemical analysis shows principally the elements V, Pb and Cu. Ca occurs as partial substitution of Pb as well as P and As in substitution to V. Minor amounts of Si and Cr were also observed. The Raman band of mottramite at 829cm−1, is assigned to the ν1 symmetric (VO4-) stretching mode. The complexity of the spectra is attributed to the chemical composition of the Tsumeb mottramite. The ν3 antisymmetric vibrational mode of mottramite is observed as very low intensity bands at 716 and 747cm−1. The series of Raman bands at 411, 439, 451cm−1 and probably also the band at 500cm−1 are assigned to the (VO4-) ν2 bending mode. The series of Raman bands at 293, 333 and 366cm−1 are attributed to the (VO4-) ν4 bending modes. The ν3, ν3 and ν4 regions are complex for both minerals and this is attributed to symmetry reduction of the vanadate unit from Td to Cs.

Vibrational Spectroscopy of the Copper (II) Disodium Sulphate Dihydrate Mineral Kröhnkite Na2Cu(SO4)2 · 2H2O

ABSTRACT A natural single-crystal specimen of the kröhnkite from Chuquicamata, Chile, with the general formula Na2Cu(SO4)2 · 2H2O, was investigated by Raman and infrared spectroscopy. The mineral kröhnkite is found in many parts of the world's arid areas. Kröhnkite crystallizes in the monoclinic crystal system with point group 2/m and space group P21/c. It is an uncommon secondary mineral formed in the oxidized zone of copper deposits, typically in very arid climates. The Raman spectrum of kröhnkite dominated by a very sharp intense band at 992 cm−1 is assigned to the ν1 symmetric stretching mode and Raman bands at 1046, 1049, 1138, 1164, and 1177 cm−1 are assigned to the ν3 antisymmetric stretching vibrations. The infrared spectrum shows an intense band at 992 cm−1. The Raman bands at 569, 582, 612, 634, 642, 655, and 660 cm−1 are assigned to the ν4 bending modes. Three Raman bands observed at 429, 445, and 463 cm−1 are attributed to the ν2 bending modes. The observation that three or four bands are seen in the ν4 region of kröhnkite is attributed to the reduction of symmetry to C2v or less.

Photoprotection in Plants Involves a Change in Lutein 1 Binding Domain in the Major Light-harvesting Complex of Photosystem II

Nonphotochemical quenching (NPQ) is the fundamental process by which plants exposed to high light intensities dissipate the potentially harmful excess energy as heat. Recently, it has been shown that efficient energy dissipation can be induced in the major light-harvesting complexes of photosystem II (LHCII) in the absence of protein-protein interactions. Spectroscopic measurements on these samples (LHCII gels) in the quenched state revealed specific alterations in the absorption and circular dichroism bands assigned to neoxanthin and lutein 1 molecules. In this work, we investigate the changes in conformation of the pigments involved in NPQ using resonance Raman spectroscopy. By selective excitation we show that, as well as the twisting of neoxanthin that has been reported previously, the lutein 1 pigment also undergoes a significant change in conformation when LHCII switches to the energy dissipative state. Selective two-photon excitation of carotenoid (Car) dark states (Car S(1)) performed on LHCII gels shows that the extent of electronic interactions between Car S(1) and chlorophyll states correlates linearly with chlorophyll fluorescence quenching, as observed previously for isolated LHCII (aggregated versus trimeric) and whole plants (with versus without NPQ).

Vibrational behavior of matrix‐isolated ions in Tutton compounds IV. Infrared spectroscopic study of NH4+ and SO42‐ ions included in nickel sulfates and selenates

AbstractInfrared spectra of K2Ni(SeO4)2·6H2O and (NH4)2Ni(SeO4)2·6H2O containing SO42‐ ions and those of K2Ni(SO4)2·6H2O and K2Ni(SeO4)2·6H2O containing NH4+ ions are presented and discussed in the region of ν3 and ν1 of the sulfate ions and in the region of ν4 of the NH4+ ions, respectively. The SO42‐ ions matrix‐isolated in the selenate matrices (approximately 1 mol%) exhibit three bands for ν3 and one band for ν1 in agreement with the low site symmetry C1 of the host selenate ions. The NH4+ guest ions included in the potassium sulfate matrix are characterized also with three bands for ν4. However, the ammonium ions in (NH4)2Ni(SeO4)2·6H2O as well as those included in K2Ni(SeO4)2·6H2O display four infrared bands corresponding to ν4 due probably to some kind of disorder of the ammonium ions. The extent of energetic distortion of the isomorphously included sulfate ions as deduced from the values of Δν3 and Δνmax is commented. The spectroscopic experiments reveal that the SO42‐ guest ions are weaker distorted in the selenate matrices as compared to the same ions in the neat sulfates due to the larger unit‐cell volumes of the selenate compounds. The band positions of the water librations in the host potassium compounds are affected by the included ammonium cations. The formation of hydrogen bonds between the NH4+ guest ions and the XO42‐ host ions leads to a decrease in the proton acceptor capabilities of the anions and as a result the hydrogen bonds weaken on going from the neat potassium compounds to the mixed crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of a Globin-coupled Oxygen Sensor with a Gene-regulating Function

Globin-coupled sensors (GCSs) are multiple-domain transducers, consisting of a regulatory globin-like heme-binding domain and a linked transducer domain(s). GCSs have been described in both Archaea and bacteria. They are generally assumed to bind O(2) (and perhaps other gaseous ligands) and to transmit a conformational change signal through the transducer domain in response to fluctuating O(2) levels. In this study, the heme-binding domain, AvGReg178, and the full protein, AvGReg of the Azotobacter vinelandii GCS, were cloned, expressed, and purified. After purification, the heme iron of AvGReg178 was found to bind O(2). This form was stable over many hours. In contrast, the predominant presence of a bis-histidine coordinate heme in ferric AvGReg was revealed. Differences in the heme pocket structure were also observed for the deoxygenated ferrous state of these proteins. The spectra showed that the deoxygenated ferrous derivatives of AvGReg178 and AvGReg are characterized by a penta-coordinate and hexa-coordinate heme iron, respectively. O(2) binding isotherms indicate that AvGReg178 and AvGReg show a high affinity for O(2) with P(50) values at 20 degrees C of 0.04 and 0.15 torr, respectively. Kinetics of CO binding indicate that AvGReg178 carbonylation conforms to a monophasic process, comparable with that of myoglobin, whereas AvGReg carbonylation conforms to a three-phasic reaction, as observed for several proteins with bis-histidine heme iron coordination. Besides sensing ligands, in vitro data suggest that AvGReg(178) may have a role in O(2)-mediated NO-detoxification, yielding metAvGReg(178) and nitrate.

X-ray diffraction and Ir-absorption characteristics of lanthanide orthophosphates obtained by crystallisation from phosphoric acid solution

Powders of LnPO4 · H2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) prepared by crystallisation from boiling phosphoric acid (2 M H3PO4/1) solution were characterised by X-ray diffraction and FTIR-spectroscopy. Hexagonal LnPO4 · H2O (La → Tb), tetragonal (Ho → Lu and Y) and orthorombic DyPO4 · H2O crystalline modifications were identified. Ir-spectra of the hydrated hexagonal, anhydrous tetragonal LnPO4 · H2O (Dy, Ho, Er, Tm, Yb, Lu and Y) and anhydrous monoclinic (La → Tb) are consistent with those reported in the literature. However, the hydrated tetragonal LnPO4 · H2O (Ho, Er, Tm, Yb, Lu and Y) display a surplus band (625 cm−1) in the region of ν4, which was not reported in the literature. The band disappears after ignition at 950°C, while the tetragonal structure is still maintained, which may imply that it is attributed to hydrogen bonding of H2O molecules to the phosphate oxygen in hydrated salts. Some of the phosphates, after ignition at 950°C, display additional P2O7 4− band at 1265–1267 cm−1. That may be resulted from HPO4 2− for PO4 3− substitution in the phosphates crystallised in acidic (2 M H3PO4/1) solution.

Raman excitation wavelength investigation of single red blood cells in vivo

AbstractRaman spectra are reported for oxygenated and deoxygenated haemoglobin contained within a single red blood cell in vivo using excitation wavelengths of 488, 514, 568 and 632.8 nm. The peak assigned in previous work to ν4 is observed at 1376 cm−1 in oxygenated cells and 1356 cm−1 in deoxygenated cells with the results from 488 nm excitation consistent with earlier Raman studies on isolated haem proteins. Exciting the cells with 514 nm radiation revealed two bands appearing in this region at 1372 and 1356 cm−1 in the oxygenated state, whereas in the deoxygenated state only one band at 1356 cm−1 is observed. At 632.8 nm excitation bands in the ν4 region appeared at 1367 and 1365 cm−1 in the oxygenated and deoxygenated states, respectively. Our results clearly show that the enhancement of bands in the vicinity of ν4 within single erythrocytes is influenced by the excitation wavelength. Furthermore, many other bands observed in oxygenated erythrocytes using 632.8 nm excitation were dramatically enhanced compared with the bands observed with other excitation wavelengths. Ruling out other explanations, it is hypothesized that the enhancement observed at 632.8 nm results from excitonic coupling between aligned porphyrins. The high concentration of haemoglobin in a single cell enables the porphyrins to be in close proximity to permit charge transfer between the haem moieties. The high signal‐to‐noise ratio and excellent reproducibility obtained using Raman water immersion microspectroscopy on single erythrocytes in vivo shows potential as a diagnostic tool for a variety of haemopathies. However, judicious choice of the excitation wavelength is a prerequisite especially if the technique is applied to diagnose oxidation status within erythrocytes. Copyright © 2002 John Wiley & Sons, Ltd.

Experimental and theoretical study of line mixing in methane spectra. IV. Influence of the temperature and of the band

Line-mixing effects are studied in infrared bands of CH4 perturbed by N2 at various pressures. The effects of temperature are investigated in the ν3 region whereas spectral shapes of the ν2, ν4, and ν3 bands are compared at room temperature. The theoretical approach proposed in preceding papers is used in order to model and analyze the influence of collisions on the spectral shape. All model parameters are now fixed to values determined in the previous studies. Comparisons between measurements and spectra computed with and without the inclusion of line mixing are made. They show that our approach satisfactorily accounts for the effects of temperature, pressure, and of rotational quantum numbers on the absorption by the ν3 band. Furthermore, the effects of collisions on spectra in the ν4 region at room temperature are also correctly calculated. On the other hand, the proposed approach fails in modeling the evolution with increasing pressure of absorption in the spectral range containing the ν2 band. This result is attributed to the Coriolis coupling between the ν2 and ν4 vibrational states and to a contribution whose physical origin remains unclear. The latter, which is negligible when CH4–He mixtures are considered, behaves as collision-induced absorption.

Simultaneous Analysis of the ν2 Raman and ν2 + ν6 Infrared Spectra of the SF6 Molecule

High-resolution Raman spectra of the ν2 band of SF6 have been recorded at a temperature of 195 K (dry ice) and a pressure of 39 mbar. These spectra were analyzed using a new set of programs specially written for XY6 molecules. These programs, called HTDS (highly spherical top data system) in reference to the set of programs called STDS (spherical top data system written for XY4 molecules) can be freely accessible through ftp (user anonymous) at f3jupiter.u-bourgogne.frf3 or on the web at the URL http://www.u-bourgogne.fr/LPUB/shTDS.html. The study of ν2 was made using a Hamiltonian developed through the third order. Four parameters were determined. The standard deviation obtained using about 559 data up to J < 61 is 0.0021 cm−1. This result is used to refine by simultaneous analysis the ν2 and ν2 + ν6 bands of SF6. This new fit allows the determination for the first time of some ν6 parameters. The values obtained for this band (forbidden in Raman and in infrared) will be used to study the infrared hot bands in the ν3 and ν4 regions.

Time-Resolved Resonance Raman Spectroscopy of Excited-State Porphyrins

Time-resolved resonance Raman (TR3) and absorbance difference studies of the excited states of Cu(TPP) (TPP=5,10,15,20-tetraphenylporphyrin) have been carried out with &lt; 10 ps times resolution in THF and pyridine solvents. In THF the distinctive transient Raman bands in the ν2 and ν4 regions, previously observed with ns laser pulses, grow in the first 55 ps before decaying in 100's of ps. The ∆A spectra also show biphasic decay. This behaviour is associated with attack by solvent on the 4-coordinate excited state to form the longer lived species observed in TR3 experiments.In pyridine two component decay is also observed but it is the shorter-lived species which gives the transient Raman bands seen previously with ns laser excitation. This state is different from that seen in THF. At 5 ps delay ν4 is broader than in the ground state and, more importantly, there is a significant shift in the two pyridine bands at ca. 1000 cm-1. This implies a significant involvement of the pyridine-based orbitals in the excited state.

Raman studies of sodium fluoroborate single crystals

AbstractRaman spectra of oriented single crystals of NaBF4 were measured at 77 and 298 K. The number of bands and the intensities were in excellent agreement with the unit cell group predictions for the known crystal structure, D, Z = 2. The results for the ν1, ν2 and ν4 regions were in excellent agreement with those of Bates [J. Chem. Phys. 55, 489 (1971)]. A recent study by Rajakumar et al. [J. Raman Spectrosc. 23, 75 (1992)] is erroneous. The new measurements permitted the assignment for the Raman bands in the ν3 region. Peaks in the external mode region were very weak because both the Na+ and BF4− ions have spherical symmetry, small polarizabilities and small polarizability derivatives with respect to normal coordinates. Only three weak peaks of the nine predicted external‐modes were observed (88 cm−1, Ag; 110 cm−1, B2g; and 214 cm−1, B2g). Crystals grown from aqueous solution were found to contain water and as much as 0.1% of BF3OH− as a substitutional impurity. Peaks due to the O–H (O–D) stretching vibration were detected in the crystals at 3641 (2688) cm−1 and peaks due to the B–OH (B–OD) stretching vibration were detected as 773 (748) cm−1.

Raman spectral studies of dehydration of Sr(BrO3)2 · H2O

AbstractRaman spectra of single‐crystal Sr(BrO3)2 · H2O were examined at 298 and 356 K from the fully hydrated to the totally anhydrous state. The Raman spectrum of the anhydrous compound, when compared with that of the hydrate, showed significant alterations in both the internal and lattice regions. The changes in the ν2–ν4 region revealed the existence of non‐equivalent BrO3− groups in the anhydrous compound. It is inferred from a relative comparison of the Raman and infrared spectra in the lattice region and thermal motion analysis that largeamplitude motions are operative for the BrO3− in the anhydrous compound.

Vibrational spectroscopy at high pressures. Part 31.—Raman and infrared spectra of rubidium and caesium nitrates

Mid-infrared and Raman spectra have been obtained for RbNO3 and CsNO3 at pressures up to at least 40 kbar in each case and up to 125 kbar for the i.r. spectra of CsNO3. The data are shown to be consistent with the recently proposed structure for RbNO3 V based upon the space group Pmmn with z= 2. The clearest evidence comes from the ν1 and ν4 regions of the nitrate ion and the libratory lattice mode region. The CsNO3 III to IV phase transition recently claimed by Kalliomäki and Meisalo on the basis of X-ray measurements has been confirmed but is shown to be extremely sluggish with phase III/IV intergrowths extending over the range 72–109 kbar.

Vibrational anharmonicity constants for SF6. I. A 16 μ diode laser study of transitions in the ν4 region

A total of eight empirical anharmonicity constants have been determined from diode laser studies of the ν4 vibrational transitions in SF6. The transitions from the low excited states on the 16 μ region were recorded using semiconductor lasers with a long optical path absorption cell. The relative intensities of the corresponding Q branches were related to the population distribution in the temperature range from 160 to 300 K in order to make the spectroscopic assignments of the ν4 hot band transitions. These measured states represent some 86% of the total population distribution of the SF6 molecules at 300 K. Theoretical models based on Morse potential functions are discussed and the results from the model calculations are compared with the experimental vibrational anharmonicity constants.

Measurements of some line positions and strengths in the ν4 region of SF6

Absolute ’’line strength’’ measurements with a diode laser spectrometer are reported for a number of J-manifolds for ν4 of SF6 in the gas phase. These results are analyzed to obtain the ν4 vibrational band strength: S0V≡A= (83±11 km mole−1. A critical discussion is presented of errors in line and band strength measurements in general, and of these results in particular. The experimental procedure was calibrated by measurements on several rotational lines in ν2 of N2O; the vibrational band strength derived for that transition in N2O is S0V=A=7.71±0.76 km mole−1, in excellent agreement with the literature value from total integrated band area measurements. The measured value for S0V for ν4 of SF6 is compared with literature values, and the discrepancy is discussed.

Vibrational Spectral Studies of Hexaquozinc Nitrate and Hexaquozinc Nitrate-d2

Infrared and Raman spectra are reported for the hexaquozinc nitrate crystal. Replacement of water by deuterium oxide causes a remarkable intensity reversal of components in the ν3 nitrate region and provides Raman spectra free from interference in the 2ν2 and ν4 regions. The nitrate spectrum is interpreted in terms of a site group approximation. The spectra are compared with those of concentrated aqueous solutions and partially dehydrated crystals to point up changes which result from a lowered site symmetry and those which result from ionic association.