Phonon dispersion of carbon nanotubes

We present the phonon dispersion relations of single-wall carbon nanotubes calculated within a force-constants approach. By using the full symmetry group of the tubes, we are able to calculate the dispersion relations for any chirality starting from one single carbon atom. We find an overbending in the highest optical branch between 6 and 12 cm⁻¹ independent of the tube diameter. The order of the high-energy modes at the Γ-point differs from the results derived from simple zone folding. The splitting between the two Raman active optical modes with A₁ symmetry at the Γ-point of chiral tubes is ≈4 cm⁻¹ for typical diameters; it increases with decreasing tube diameter.     

Raman spectra of proton order of thin ice Ih film

The polarized Raman spectra of the upper part of a thin ice Ih film were obtained in the range of 150 cm⁻¹ to 3800 cm⁻¹. The spectra showed clear polarization dependence; several new peaks were also observed. The longitudinaloptic–tranverseoptic (LO–TO) splitting of the mode near 220 cm⁻¹ in the translational vibration region was experimentally confirmed at 133 K. The Fermi resonance between the bending overtone (around 3270 cm⁻¹) and symmetry stretching fundamental (around 3350 cm⁻¹) in the stretching vibration region appeared at nearly the same temperature. Results showed that ice XI (i.e. proton‐ordered phase of ice Ih) slowly formed in the upper part of a thin ice Ih film without KOH as the temperature gradually decreased below 133 K. Copyright © 2015 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering and fluorescence emission of gold nanoparticle–multiwalled carbon nanotube hybrids

Multiwalled carbon nanotubes (MWCNTs) are grafted with gold (Au) nanoparticles of different sizes (1–12 and 1–20 nm) to form Au–MWCNT hybrids. The Au nanoparticles pile up at defect sites on the edges of MWCNTs in the form of chains. The micro‐Raman scattering studies of these hybrids were carried using visible to infrared wavelengths (514.5 and 1064 nm). Enhanced Raman scattering and fluorescence is observed at an excitation wavelength of 514.5 nm. It is found that the graphitic (G) mode intensity enhances by 10 times and down shifts by approximately 3 cm⁻¹ for Au–MWCNT hybrids in comparison with pristine carbon nanotubes. This enhancement in G mode due to surface‐enhanced Raman scattering effect is related to the interaction of MWCNTs with Au nanoparticles. The enhancement in Raman scattering and fluorescence for large size nanoparticles for Au–MWCNTs hybrids is corroborated with localized surface plasmon polaritons. The peak position of localized surface plasmons of Au nanoparticles shifts with the change in environment. Further, no enhancement in G mode was observed at an excitation wavelength of 1064 nm. However, the defect mode (D) mode intensity enhances, and peak position is shifted by approximately 40 cm⁻¹ to lower side at the same wavelength. The enhanced intensity of D mode at 1064 nm excitation wavelength is related to the double resonance phenomenon and shift in the particular mode occurs due to more electron phonon interactions near Fermi level. Copyright © 2012 John Wiley & Sons, Ltd.     

Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6‐mm‐thick sulfur specimen at 1500 m

The absolute Raman scattering cross sections (σ_RS) for the 471, 217, and 153 cm⁻¹ modes of sulfur were measured as 6.0 ± 1.2 × 10⁻²⁷, 7.7 ± 1.6 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁶ cm² at 815, 799, and 794 nm, respectively, using a 785‐nm pump laser. The corresponding values of σ_RS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10⁻²⁷, 1.2 ± 0.24 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁷ cm² using a 1064‐nm laser. A temperature‐controlled, small‐cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6‐mm‐thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4‐W, CW, 785‐nm pump laser. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

The interaction of K⁺ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm⁻¹. The wavenumber position of the band at ~529 cm⁻¹ shows a red shift of 14 cm⁻¹, while the Raman band at ~634 cm⁻¹ shows a blue shift of 10 cm⁻¹ with the increasing x from 1 to 5 M. The intensity ratio I₆₃₄/I₅₂₉ is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K⁺] complex in the solution. The new Raman band appeared at ~1079 cm⁻¹ in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K⁺ with ZAla, the structures of ZAla and the [ZAla + K⁺] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO⁻, and therefore, COO⁻ would be the most probable site for the interaction of K⁺ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K⁺] and the [ZAla⁻ + K⁺] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm⁻¹ may be used as the Raman fingerprint for the interaction of K⁺ with COO⁻ of the ZAla and ZAla⁻. Copyright © 2015 John Wiley & Sons, Ltd.     

High concentration trans form unsaturated lipids detected in a HeLa cell by Raman microspectroscopy

High concentration trans form unsaturated lipids have been found in a HeLa cell by Raman microspectroscopy. Two CC stretch bands are observed simultaneously at 1669 cm⁻¹ (trans form) and at 1656 cm⁻¹ (cis form) in a Raman spectrum obtained from a small area (1 µm in diameter) in a HeLa cell. The intensity ratio 1669/1656 indicates that the concentration of the trans form is as high as that of the cis. It is demonstrated that Raman microspectroscopy provides a powerful and unique means for in situ and noninvasive structural characterization of unsaturated lipids in a living cell. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies of the structure of di‐amino acid peptides. Part II: cyclo(L‐Asp‐L‐Asp) in the solid state and in aqueous solution

Solid‐state protonated and N,O‐deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di‐amino acid peptide cyclo(L ‐Asp‐L ‐Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3‐LYP/cc‐pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L ‐Asp‐L ‐Asp), assuming C₂ symmetry, predicts a boat conformation for the DKP ring with both the two L ‐aspartyl side chains being folded slightly above the ring. The CO stretching vibrations have been assigned for the side‐chain carboxylic acid group (e.g. at 1693 and 1670 cm⁻¹ in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm⁻¹ in the Raman spectrum). The presence of two bands for the carboxylic acid CO stretching modes in the solid‐state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm⁻¹ in the solid‐state Raman spectrum, which is in agreement with results for cyclic di‐amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C^α atom is increased, the amide II band wavenumber decreases to below 1500 cm⁻¹; this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm⁻¹), which indicates that this band has a smaller N H bending contribution than the trans amide II vibrational band observed for linear peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman‐induced Kerr effect spectroscopy of single‐wall carbon nanotubes aqueous suspensions in the range 0.1–10 and 100–250 cm−1

Here, we study a low (less than 0.1 µg/ml) concentration aqueous suspension of single‐wall carbon nanotubes (SWNTs) by Raman‐induced Kerr effect spectroscopy (RIKES) in the spectral bands 0.1–10 and 100–250 cm⁻¹. This method is capable of carrying out direct investigation of SWNT hydration layers. A comparison of RIKES spectra of SWNT aqueous suspension and that of milli‐Q water shows a considerable growth in the intensity of low wavenumber Raman modes. These modes in the 0.1–10 cm⁻¹ range are attributed to the rotational transitions of H₂O₂ and H₂O molecules. We explain the observed intensity increase as due to the production of hydrogen peroxide and the formation of a low‐density depletion layer on the water–nanotube interface. A few SWNT radial breathing modes (RBM)are observed (ω_RBM = 118.5, 164.7 and 233.5 cm⁻¹) in aqueous suspension, which allows us to estimate the SWNT diameters (∼2.0, 1.5, and 1 nm, respectively). Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the mineral finnemanite Pb5(As3+O3)3Cl

The arsenite mineral finnemanite Pb₅(As³⁺ O₃)₃Cl has been studied by Raman spectroscopy. The most intense Raman band at 871 cm⁻¹ is assigned to the ν₁(AsO₃)³⁻ symmetric stretching vibration. Three Raman bands at 898, 908 and 947 cm⁻¹ are assigned to the ν₃(AsO₃)³⁻ antisymmetric stretching vibration. The observation of multiple antisymmetric stretching vibrations suggest that the (AsO₃)³⁻ units are not equivalent in the molecular structure of finnemanite. Two Raman bands at 383 and 399 cm⁻¹are assigned to the ν₂(AsO₃)³⁻ bending modes. Density functional theory enabled calculation of the position of AsO₃²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹ and the deformation mode at 449 cm⁻¹. Raman bands are observed at 115, 145, 162, 176, 192, 216 and 234 cm⁻¹ as well. The two most intense bands are observed at 176 and 192 cm⁻¹. These bands are assigned to PbCl stretching vibrations and result from transverse/longitudinal splitting. The bands at 145 and 162 cm⁻¹ may be assigned to Cl Pb Cl bending modes. Copyright © 2009 John Wiley & Sons, Ltd.     

OctTES/TEOS system for hybrid coatings: real‐time monitoring of the hydrolysis and condensation by Raman spectroscopy

The hybrid organic–inorganic system Tetra‐ethyl‐ortho‐silicate functionalized with Octyl‐triethoxy‐silane, studied as protective coating for the preservation of historical glasses from the environmental weathering agents, has been characterized by Raman spectroscopy by monitoring the sol‐gel reactions over time through characteristic features in the spectrum. In particular, for the hydrolysis reaction the disappearance of the 653 cm⁻¹ (Si‐O symmetric breathing) and 810 cm⁻¹ (CH₂ rocking in Si‐alkoxides) peaks and the growth of the 710 cm⁻¹ band, because of hydrolyzed alkyl‐silane, and of the 881 cm⁻¹ peak (ethanol C–C symmetric stretching) have been checked. Moreover, the condensation reaction can be tracked by the disappearance of the two main peaks of the alcohols at 816 and 881 cm⁻¹, going along with the growth of the broad band between 250 and 500 cm⁻¹ (Si–O–Si symmetric bending) and of the feature at 840 cm⁻¹ (Si–O–Si stretching). At the end of the condensation process the Raman spectrum still displays spectral bands unique to the alkyl chain in Octyl‐triethoxy‐silane, in the 1330–1450 cm⁻¹ and 2725–3000 cm⁻¹ ranges. Copyright © 2016 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the tellurite minerals: emmonsite Fe23+Te34+O9·2H2O and zemannite Mg0.5[Zn2+Fe3+(TeO3)3]4.5H2O

Raman spectroscopy has been used to study zemannite Mg_0.5[Zn²⁺Fe³⁺(TeO₃)₃]4.5H₂O and emmonsite Fe₂³⁺Te₃⁴⁺O₉·2H₂O. Raman bands for zemannite and emmonsite, observed at 740 and 650 cm⁻¹ and at 764 and 788 cm⁻¹, respectively, are attributed to the ν₁ (TeO₃)²⁻ symmetric stretching mode. The splitting of the symmetric stretching mode for emmonsite is in harmony with the results of X‐ray crystallography which shows three non‐equivalent TeO₃ units in the crystal structure. Two bands at 658 and 688 cm⁻¹ are assigned to ν₃ (TeO₃)²⁻ anti‐symmetric stretching modes. Raman bands observed at 372 and 408 cm⁻¹ for zemannite and 397 and 414 cm⁻¹ for emmonsite are attributed to the (TeO₃)²⁻ν₂(A₁) bending mode. The two Raman bands at 400 and 440 cm⁻¹ for emmonsite are ascribed to the ν₄(E) bending modes, while the band at 326 cm⁻¹ is due to the ν₂(A₁) bending vibration. Copyright © 2008 John Wiley & Sons, Ltd.     

Visible,near‐infrared,and ultraviolet laser‐excited Raman spectroscopy of the monocytes/macrophages (U937) cells

Raman spectra of the monocytes were recorded with laser excitation at 532, 785, 830, and 244 nm. The measurements of the Raman spectra of monocytes excited with visible, near‐infrared (NIR), and ultraviolet (UV) lasers lad to the following conclusions. (1) The Raman peak pattern of the monocytes can be easily distinguished from those of HeLa and yeast cells; (2) Positions of the Raman peaks of the dried cell are in coincidence with those of the monocytes in a culture cell media. However, the relative intensities of the peaks are changed: the peak centered around 1045 cm⁻¹ is strongly intensified. (3) Raman spectra of the dead monocytes are similar to those of living cells with only one exception: the Raman peak centered around 1004 cm⁻¹ associated with breathing mode of phenylalanine is strongly intensified. The Raman spectra of monocytes excited with 244‐nm UV laser were measured on cells in a cell culture medium. A peak centered at 1485 cm⁻¹ dominates the UV Raman spectra of monocytes. The ratio I₁₅₇₄/I₁₆₁₃ for monocytes is found to be around 0.71. This number reflects the ratio between proteins and DNA content inside a cell and it is found to be twice as high as that of E. coli and 5 times as high as that of gram‐positive bacteria. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Raman signature for the formation of CdO/MnO2 (core/shell) nanostructures

In the present report, bare CdO and CdO/MnO₂ core/shell nanostructures of various cores and different shell sizes were synthesized using co‐precipitation method. The phase, size, shape and structural details of the bare CdO and CdO/MnO₂ nanostructures were investigated by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy measurements. TEM micrographs confirm the formation of core/shell nanostructures. The presence of CdO (core) and MnO₂ (shell) crystal phases was determined by analyzing the Raman data of bare CdO and CdO/MnO₂ core/shell nanostructures. The Raman spectra of bare CdO nanostructures contain one broad intense convoluted envelop of three bands in the spectral range of 200–500 cm⁻¹ and a weaker band located at ~940 cm⁻¹. The intensity of these two Raman bands is decreased with the increase of shell size and disappeared completely for the shell size 5.3 ± 1 nm. Further, two new Raman bands appeared at ~451 and ~665 cm⁻¹ for the shell size 1.3 ± 0.1 nm. These two Raman bands are assigned to the deformation of Mn–O–Mn and Mn–O stretching modes of MnO₂. The intensity of these two Raman bands is enhanced with the increase of shell size and attains a maximum value for the shell size 5.3 ± 1 nm. The disappearance of characteristics Raman bands of CdO phase and the appearance of characteristics Raman bands corresponding to MnO₂ phase for nanostructures of shell size 5.3 ± 1 nm authenticate the presence of CdO as core and MnO₂ as shell in the core/shell nanostructures. Copyright © 2014 John Wiley & Sons, Ltd.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

Davydov doublets in Raman spectra of ϵ-GaSe

Raman scattering spectra of ϵ-GaSe and β-Gas crystals were examined at temperature 8° and 295°K with a resolution of 0.7 cm⁻¹. At low temperature the Davydov splitting of modes in ϵ-GaSe could be accurately measured. The largest splitting of the Raman bands in ϵ-GaSe was found to be about 3 cm⁻¹ and correlates well with that predicted from a model based on the molecular nature of this compound.     

The design of a peptide linker group to enhance the SERS signal intensity of an atto680 dye‐nanoparticle system

The Surface enhanced resonance Raman spectroscopy (SERRS) spectra of three modified atto680 dyes were recorded using Au nanoparticles and an excitation laser operating at 670 nm. The dyes were modified with linker groups based on the small peptides, Cys, Cys–Gly and Cys–Gly–Gly. The Cys thiol group acted as the coupling point to the Au surface and the Gly  NH₂ group used to attach the dye. The maximum signal was recorded for the Cys–Gly linker. This gave a signal intensity for the 577 cm⁻¹ Raman peak of the atto680 dye that was more than 27 times greater than the unmodified dye. The Au nanoparticles used had a diameter of 49.8 ± 1.2 nm and were synthesised by the citrate reduction method. The Raman dye‐AuNP probes were also used in an immunoassay to detect mouse IgG in the femto mole range. Copyright © 2010 John Wiley & Sons, Ltd.     

Dussertite BaFe3+3(AsO4)2(OH)5—a Raman spectroscopic study of a hydroxy‐arsenate mineral

The mineral dussertite, a hydroxy‐arsenate mineral with formula BaFe³⁺₃(AsO₄)₂(OH)₅, has been studied by Raman spectroscopy complemented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved to be quite similar, although some minor differences were observed. In the Raman spectra of the Czech dussertite, four bands are observed in the 800–950 cm⁻¹ region. The bands are assigned as follows: the band at 902 cm⁻¹ is assigned to the (AsO₄)³⁻ν₃ antisymmetric stretching mode, the one at 870 cm⁻¹ to the (AsO₄)³⁻ν₁ symmetric stretching mode, and those at 859 and 825 cm⁻¹ to the As‐OM^{2 + /3+} stretching modes and/or hydroxyl bending modes. Raman bands at 372 and 409 cm⁻¹ are attributed to the ν₂ (AsO₄)³⁻ bending mode and the two bands at 429 and 474 cm⁻¹ are assigned to the ν₄ (AsO₄)³⁻ bending mode. An intense band at 3446 cm⁻¹ in the infrared spectrum and a complex set of bands centred upon 3453 cm⁻¹ in the Raman spectrum are attributed to the stretching vibrations of the hydrogen‐bonded (OH)⁻ units and/or water units in the mineral structure. The broad infrared band at 3223 cm⁻¹ is assigned to the vibrations of hydrogen‐bonded water molecules. Raman spectroscopy identified Raman bands attributable to (AsO₄)³⁻ and (AsO₃OH)²⁻ units. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the selenite mineral: ahlfeldite,NiSeO3·2H2O

Raman spectroscopy has been used to study the selenite mineral ahlfeldite. A comparison is made with the Raman spectra of chalcomenite, cobaltomenite and clinochalcomenite. Selenite minerals are characterised by the position of the symmetric stretching mode which is observed at higher wavenumbers than the anti‐symmetric stretching mode. The selenite ion has C_3v symmetry and four modes, 2A₁ and 2E. These modes are observed at 813, 472 cm⁻¹ (A₁) and 685, 710, 727 and 367 and 396 cm⁻¹ (E). Bands assigned to the water stretching vibrations are observed for ahlfeldite at 3385 cm⁻¹, for chalcomenite at 2953, 3184 and 3506 cm⁻¹ and for clinochalcomenite at 2909, 3193 and 3507 cm⁻¹. A comparison of the Raman spectra of chalcomenite, clinochalcomenite and cobaltomenite is made. The position of these bands enabled hydrogen bond distances in the selenite structure to be estimated. Hydrogen bond distances for ahlfeldite, chalcomenite and clinochalcomenite were determined to be similar. Copyright © 2008 John Wiley & Sons, Ltd.     

Confocal Raman microscopy for monitoring the membrane polymerization and thermochromism of individual,optically trapped diacetylenic phospholipid vesicles

Optical‐trapping confocal Raman microscopy allows the 1, 4‐addition reaction of diacetylenic functional groups in 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine lipids to be monitored in individual phospholipid vesicles. Optical trapping allows a single vesicle to be observed over time, allowing the direct observation of structural changes in the vesicle membrane during polymerization. Confocal Raman microscopy excludes light collection outside the optical‐trap region avoiding interferences from the surrounding solution, while chemical reactions occurring in the membrane of the trapped vesicle can be measured with high sensitivity. Individual, optically trapped liposomes (0.6 µm in diameter) were exposed to photolysis radiation at 254 nm. Upon exposure to UV light, the cross‐linking polymerization reaction formed a conjugated ene–yne backbone in the bilayer of the optically trapped vesicle. Polymerization produces two different polymers, red and yellow in color, which can be distinguished structurally by their Raman spectra. Rates of red and yellow polymer formation were monitored by the Raman scattering intensities from both C = C stretching vibrations at 1455 cm^–1 and 1508 cm^–1 and C ≡ C stretching vibrations at 2080 and 2110 cm^–1, respectively. Polymer formation rates depended linearly on 254‐nm light intensity, consistent with a one‐photon excited polymerization reacting in a photostationary state. Relative populations of red and yellow polymer in a polymerized vesicle depend sensitively on the sample temperature. From temperature‐dependent Raman spectra, the enthalpy change of the red‐to‐yellow thermochromic response and corresponding structural changes in the polymer could be determined. Copyright © 2011 John Wiley & Sons, Ltd.     

Natural halotrichites—an EDX and Raman spectroscopic study

Raman spectroscopy has been used to characterise four natural halotrichites: halotrichite FeSO₄.Al₂(SO₄)₃. 22H₂O, apjohnite MnSO₄.Al₂(SO₄)₃.22H₂O, pickingerite MgSO₄.Al₂(SO₄)₃.22H₂O and wupatkiite CoSO₄.Al₂(SO₄)₃.22H₂O. A comparison of the Raman spectra is made with the spectra of the equivalent synthetic pseudo‐alums. Energy dispersive X‐ray analysis (EDX) was used to determine the exact composition of the minerals. The Raman spectrum of apjohnite and halotrichite display intense symmetric bands at ∼985 cm⁻¹ assigned to the ν₁(SO₄)²⁻ symmetric stretching mode. For pickingerite and wupatkiite, an intense band at ∼995 cm⁻¹ is observed. A second band is observed for these minerals at 976 cm⁻¹ attributed to a water librational mode The series of bands for apjohnite at 1104, 1078 and 1054 cm⁻¹, for halotrichite at 1106, 1072 and 1049 cm⁻¹, for pickingerite at 1106, 1070 and 1049 cm⁻¹ and for wupatkiite at 1106, 1075 and 1049 cm⁻¹ are attributed to the ν₃(SO₄)²⁻ antisymmetric stretching modes of ν₃(B_g) SO₄. Raman bands at around 474, 460 and 423 cm⁻¹ are attributed to the ν₂(A_g) SO₄ mode. The band at 618 cm⁻¹ is assigned to the ν₄(B_g) SO₄ mode. The splitting of the ν₂, ν₃ and ν₄ modes is attributed to the reduction of symmetry of the SO₄ and it is proposed that the sulphate coordinates to water in the hydrated aluminium in bidentate chelation. Copyright © 2007 John Wiley & Sons, Ltd.