A Vibrational Spectroscopic Study of the So-Called Healing Mineral Papagoite CaCuAlSi2O6(OH)3

ABSTRACT

Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi₂O₆(OH)₃ is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu²⁺ in square planar coordination.

The intense sharp Raman band at 1053 cm^?1 is assigned to the ν₁ (A _1g) symmetric stretching vibration of the SiO₄ units. The splitting of the ν₃ vibrational mode offers support to the concept that the SiO₄ tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm^?1 with a shoulder at 644 cm^?1 is assigned to the ν₄ vibrational modes.

Intense Raman bands at 419 and 460 cm^?1 are attributed to the ν₂ bending modes.

Intense Raman bands at 3545 and 3573 cm^?1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm^?1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi₂O₆(OH)₃ · xH₂O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.     

Vibrational spectroscopy of oxygen on the (100) and (111) surfaces of lanthanum hexaboride

Reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS) have been used to study the adsorption of oxygen on the (100) and (111) surfaces of lanthanum hexaboride. Exposure of the surface at temperatures of 95 K and above to O₂ produces atomic oxygen on the surface and yields vibrational peaks in good agreement with those observed in previous HREELS studies. On the La-terminated (100) surface, RAIRS peaks correspond to vibrations of the boron lattice that gain intensity due to a decrease in screening of surface dipoles that accompanies oxygen adsorption. A sharp peak at ～ 734 cm^?1 in the HREEL spectrum shows isotopic splitting with RAIRS into two components at 717 and 740 cm^?1 with full widths at half maxima of only 12 cm^?1. The sharpness of this mode is consistent with its interpretation as a surface phonon that is well separated from both the bulk phonons and other surface phonons of LaB₆. On the boron-terminated LaB₆(111) surface, broad and weak features are assigned to both vibrations of the boron lattice and of boron oxide. On the (100) surface, oxygen blocks the adsorption sites for CO, and adsorbed CO prevents the dissociative adsorption of O₂.     

Ethylene-oxide adsorption on Ni(111): Hreels and Arups investigations

The adsorption of ethylene-oxide (Et-O) on Ni(111) was studied with high resolution electron energy loss spectroscopy and angular resolved UV-light induced photoelectron spectroscopy (ARUPS) at 140K; these measurements were complemented by thermal desorption spectroscopy (TDS) and workfunction change measurements ( δφ ).For fractional Et-O monolayer coverages five loss peaks were observed with HREELS at 835, 1155, 1270, 1495 and 3150 cm⁻¹ which are attributed to the C₂O ring deformation, CH₂ wagging and twisting modes, to the C₂O ring breathing, to the CH₂ scissor modes and C-H stretching modes of molecular adsorbed Et-O. At low coverage, the HREELS is dominated by the 835 and 3150 cm⁻¹ losses, whereas the 1155, 1270 and 1495 cm⁻¹show only weak intensities. The latter loss peaks increase significantly in intensity for Et-O coverage near the saturation of the first adsorption layer, θ (Et-O)~0.3.UPS measurements confirm the molecular adsorption of Et-O on Ni(111) at 140 K. Compared to the Et-O gas phase UPS, a considerable shift to lower binding energy is observed for the 6a₁ oxygen lone pair orbital and also for the 2b₁ (n, σ_CO, σ_CC) which has some lone pair character. These chemical shifts suggest a bonding of Et-O to Ni(111) through the oxygen atom.     

The adsorption of cyclic hydrocarbons on Ru(001): I. Cyclopropane

The adsorption of cyclopropane on Ru(001) at 90 K has been investigated by high-resolution electron energy loss spectroscopy, He I photoelectron spectroscopy, low-energy electron diffraction and thermal desorption mass spectrometry. The results indicate that the molecule adsorbs nondissociatively without long-range order and that no opening of the carbon ring occurs. The adsorption bond is weak, and multilayers form at 90 K only in the presence of a relatively high c-C₃H₆ equilibrium pressure. The vibrational spectrum is characterized by strong, dipole-active ring deformation modes and an additional mode at 570 cm^?1, which is due to a frustrated translation of the admolecule perpendicular to the surface with some ring deformation character. The photoelectron spectrum is characterized by a Jahn-Teller splitting of the 3e' molecular orbital, which is observed also in the gas phase. With the exception of a uniform relaxation shift, no other shifts could be observed in comparison with the gas phase. The results are discussed in relation to possible bonding mechanisms.     

Raman spectroscopic study of the magnesium carbonate mineral hydromagnesite (Mg5[(CO3)4(OH)2]· 4H2O)

Magnesium minerals are important for understanding the concept of geosequestration. One method of studying the hydrated hydroxy magnesium carbonate minerals is through vibrational spectroscopy. A combination of Raman and infrared spectroscopy has been used to study the mineral hydromagnesite. An intense band is observed at 1121 cm⁻¹, attributed to the CO₃²⁻ν₁ symmetric stretching mode. A series of infrared bands at 1387, 1413 and 1474 cm⁻¹ are assigned to the CO₃²⁻ν₃ antisymmetric stretching modes. The CO₃²⁻ν₃ antisymmetric stretching vibrations are extremely weak in the Raman spectrum and are observed at 1404, 1451, 1490 and 1520 cm⁻¹. A series of Raman bands at 708, 716, 728 and 758 cm⁻¹ are assigned to the CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum in the OH stretching region is characterized by bands at 3416, 3516 and 3447 cm⁻¹. In the infrared spectrum, a broad band is found at 2940 cm⁻¹, which is assigned to water stretching vibrations. Infrared bands at 3430, 3446, 3511, 2648 and 3685 cm⁻¹ are attributed to MgOH stretching modes. 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.     

Vibrational spectra of ethylene and acetylene on metal surfaces - an electron energy loss study of ethylene adsorbed on Ni(110) and its carbided surface,and the use of metal-cluster analogies

An analysis has been made of on- and off-specular electron energy loss spectra (EELS) from C₂H₄ and C₂D₄ adsorbed on a clean Ni(110) and also a carbided Ni(110) surface. The carbided surface was prepared by heating the clean Ni surface in ethylene to 573 K or above. EELS spectra were obtained using a Leybold-Heraeus spectrometer at a beam energy of 3.0 eV and with a resolution of ca. 6.5 meV (ca. 50 cm^?1).The loss spectrum from ethylene at low temperatures (110 K) showed principal features at 3000 (w), 1468 (w), 1162 (s), 879 (w) and 403 cm^?1 (s) (C₂D₄ adsorption) and 2186 (w), 1258 (ms), 944 (ms), 645 (w) and 400 cm^?1 (s) (C₂D₄ adsorption). The overall pattern of wavenumbers and intensifies of the C₂H₄/C₂D₄ loss peaks is very similar in form (although systematically different in positions) to those previously observed on Ni(111) (ref.1) and Pt(111) (ref.2) surfaces at low temperatures. Like these earlier spectra,the EELS results for C₂H₄/C₂D₄ adsorbed on clean Ni(110) can be well interpreted in terms of a MCH₂CH₂M/MCD₂CD₂M species (M = metal) with the CC bond parallel to the surface.After adsorption on the carbided Ni(110) surfaces at 125 K,the main loss features occur at 3065 (m), 2992 (m), 1524 (ms), 1250 (s), 895 (s), and 314 cm^?1 (vs) (C₂H₄ adsorption) and 2339 (m), 2242 (m), 1395 (s), 968 (s), 661 (m) and 314 cm^?1 (vs). With the exceptions of reduced intensities of the bands at 895 cm^?1 (C₂H₄) and 661 cm^?1 (C₂D₄) this pattern of losses - particularly the 1550-1200 cm^?1 features which can be assigned to coupled νCC and δCH₂/δCD₂ modes - is well related to similar results on Cu(100) (ref.3) and Pd(111) (ref.4) which have been interpreted convincingly in terms of the presence of π-bonded species, (C₂H₄)M or (C₂D₄)M on the surface. This structural assignment is supported by comparison with the vibrational spectra of Zeise's salt, K[PtCl₃(C₂H₄)].H₂O (refs.5&6).Spectral changes occur on warming C₂H₄ on the clean Ni(110) surface with a growth of a feature near 895 cm^?1 at 200 K. At 300 K a rather poorly-defined spectrum occurs, which differs substantially from those found on (111) surfaces of Pt (ref.2), Rh (ref.7) or Pd (ref.8) at room temperature. These latter have been attributed to the ethylidyne, CH₃.CM₃, surface species (ref.9). For adsorption on Ni(110) there is clearly a mixture of species at room temperature.The analysis of the vibrational spectra of selected metal-cluster compounds of known structure with selected hydrocarbon ligands has helped substantially to assign the spectra of surface species in terms of bonding structures of the adsorbed species, as in the cases of the identification of (C₂H₄)M π-adsorbed (refs.5&6) and the ethylidyne CH₃.CM₃ species (ref.9). We have recently analysed the infrared and Raman spectra of the cluster compound (C₂H₂)Os₃(CO)₁₀ and its deuterium-containing analogue. The infrared frequency and intensity pattern for the A′ modes (C_S symmetry) of the two isotopomers bears a remarkable resemblance to EELS spectra previously obtained at low temperature for C₂H₂/C₂D₂ adsorbed on Pt(111) (ref.2) and (after taking into account systematic frequency shifts) for Pd(111) (ref.4). There is good evidence for believing that the structure of the hydrocarbon ligand interacting with the osmium complex takes the form

where the arrow denotes a π-bond to the third metal atom. This strongly confirms the structure for the low-temperature acetylene species on Pt(111) as proposed by Ibach and Lehwald (ref.2).Finally the room-temperature spectra for ethylene adsorbed on finely-divided silica-supported Pt and Pd catalysts have previously been interpreted in terms of the presence of MCH₂CH₂M (ref.10) and π-bonded (C₂H₄)M species (ref.11). However comparisons with the more recent EELS spectra from ethylene on Pt(111) at room temperature (ref.2) now leads to a reassignment of the 2880 cm^?1 band, on Pt, previously assigned to MCH₂CH₂M, together with a new, related,band at 1340 cm^?1 (ref.12), to the ethylidyne species CH₃CPt₃ found on the single crystal surface.More detailed analyses of the spectra reported here will be published later. Acknowledgement is given to substantial assistance for this programme of research from the Science and Engineering Research Council.     

New vibrational assignments in the Ā1 Au-[Xtilde] 1Σ+ g electronic transition of acetylene,C2H2: the v′1 frequency

New laser-induced fluorescence spectra of supersonic jet cooled acetylene (C₂H₂) in the wavelength region 230–205 nm have led to an improved understanding of the vibrational structure of the A ¹A_u state. Among the new bands observed are two weak perturbed bands at 46008 cm^?1 and 46116 cm^?1. Rotational analyses of these bands, together with the corresponding ‘hot’ bands arising from the ground state v4 fundamental, have shown that the upper states have asymmetric top K structure that is unaffected by a axis Coriolis coupling; this means that they do not involve overtones of the low frequency bending vibrations and therefore must be combinations of a_g vibrational normal modes. From their positions in the manifold, their vibrational assignments can only be 2² ₀3¹ ₀; and 1¹ ₀;3¹ ₀. These assignments lead to values of x ₂₂, x₁₃, and a revised value for the symmetric CH stretching frequency, ν₁ = 2880.5cm^?1; this revised value is 160cm^?1 lower than the previously accepted value, but consistent with new ab initio calculations that we performed at the EOM-CCSD level using a TZ2P (triple-zeta plus double polarization) basis set.     

Identification of surface vibrations on clean and oxygen covered Pt(111) surfaces with high resolution electron energy loss spectroscopy (EELS)

Clean and oxygen covered {111} recrystallized Pt surfaces were studied by EELS after surface preparation at 150≤T≤165OK. The clean surface shows Stokes as well as anti-Stokes lines of surface phonons at ±195^?1. Adsorption of small amounts of (<10^?2 monolayers) of O₂ or H₂ leads to substrate-derived phonon losses at ±380cm^?1. Oxygen exposure at different pressures, times and temperatures leads to atomic and/or molecular adsorption as well as oxide-related features which have been identified by EELS.     

Neutron inelastic spectroscopy of benzene chemisorbed on Raney platinum

The neutron inelastic scattering spectrum of benzene adsorbed at 300 K on Raney platinum has been measured between 350 and 2250 cm^?1. No deshydrogenation of the molecules is observed so that the benzene ring must be adsorbed parallel to the surface. Slight modifications of the force field of the model molecule (C₆H₆)Cr(CO)₃ were introduced to account for the vibrational frequency shifts. The benzene molecule is found less perturbed on platinum than on nickel. The calculated frequencies of adsorbed C₆H₆ and C₆D₆ are used to reassign some modes previously observed by electron loss spectroscopy.     

Vibrational Spectroscopic Characterization of the Sulphate-Carbonate Mineral Burkeite: Implications for Evaporites

Burkeite formation is important in saline evaporites and in pipe scales. Burkeite is an anhydrous sulphate-carbonate with an apparent variable anion ratio. Such a formula with two oxyanions lends itself to vibrational spectroscopy. Two symmetric sulphate stretching modes are observed, indicating at least at the molecular level the nonequivalence of the sulphate ions in the burkeite structure. The strong Raman band at 1065 cm^?1 is assigned to the carbonate symmetric stretching vibration. The series of Raman bands at 622, 635, 645, and 704 cm^?1 are assigned to the ν₄ sulphate bending modes. The observation of multiple bands supports the concept of a reduction in symmetry of the sulphate anion from T _d to C _3v or even C _2v.     

Raman microscopy of haidingerite Ca(AsO3OH)·H2O and brassite Mg(AsO3OH)·4H2O

Raman spectroscopy has been used to study the arsenate minerals haidingerite Ca(AsO₃OH)·H₂O and brassite Mg(AsO₃OH)·4H₂O. Intense Raman bands in the haidingerite spectrum observed at 745 and 855 cm⁻¹ are assigned to the (AsO₃OH)²⁻ν₃ antisymmetric stretching and ν₁ symmetric stretching vibrational modes. For brassite, two similarly assigned intense bands are found at 809 and 862 cm⁻¹. The observation of multiple Raman bands in the (AsO₃OH)²⁻ stretching and bending regions suggests that the arsenate tetrahedrons in the crystal structures of both minerals studied are strongly distorted. Broad Raman bands observed at 2842 cm⁻¹ for haidingerite and 3035 cm⁻¹ for brassite indicate strong hydrogen bonding of water molecules in the structure of these minerals. OH···O hydrogen‐bond lengths were calculated from the Raman spectra based on empirical relations. Copyright © 2009 John Wiley & Sons, Ltd.     

A vibrational characterisation of the O/A1(111) system: a reassignment of HREELS data

In light of recent STM measurements of the O/A1(111) system, we reassign the dipole active modes observed at low coverage to resolve discrepancies between the interpretation of Strong, Firey, deWette and Erskine [Phys. Rev. B 26 (1982) 3483], invoking subsurface oxygen, and a variety of other studies which find no evidence for surface oxygen. The STM results, which show that very small island sizes are stabilized over an exposure range up to ∼ 200 L with a total coverage ≤ 0.2 ML, are incompatible with the assumption of long range periodicity required for lattice dynamical modeling. The consequence is that vibrational modes polarized parallel to the surface may become dipole active. Within an Al₃O cluster model appropriate to exposures ≤ 3 L where most oxygen atoms are isolated species in three-fold hollow sites, the strong feature at 584 cm⁻¹ (72 meV) is still attributed to top-layer oxygen motion perpecdicular to the surface (the symmetric Al₃O stretch) but the second intense feature at 480 cm⁻¹ (60 meV) is assigned to the umbrella mode involving predominantly Al motion parallel to the surface rather than the motion of two AlO layers moving perpendicular to the surface out of phase with each other. The lowest frequency mode near 224 cm⁻¹ (28 meV) derives from the frustrated translation of the cluster perpendicular to the surface. At higher exposures (> 10 L) where multiple oxygen islands begin to appear, totally symmetric combinations of the E-derived asymmetric Al₃O stretching motion polarised nominally parallel to the surface become dipole allowed and can be assigned to the loss at 850 cm⁻¹ (105 meV), which was previously attributed to subsurface oxygen.     

Photophysical studies of uranyl complexes 5. Luminescence spectrum of K4UO2(CO3)3

The photoluminescence of K₄UO₂(CO₃)₃ has been studied under conditions of high resolution at cryogenic temperatures. The origin corresponding to the pure electronic transition was located at 4774 Å (20945 cm^-1), and it was found that the totally symmetric uranyl stretching mode was coupled to this transition. A progression of four band systems thus resulted, and from an examination of the energies of corresponding peaks in each system, a value of 813 cm^-1 for the U-O stretching mode was determined. Two lattice modes (34 and 80 cm^-1) and two molecular vibrational modes (205 and 276 cm^-1) were also found to couple with the pure electronic transition, thus yielding approximately 15 major peaks in each band system. The 205 cm^-1 vibration corresponded to a CO^2-₃ vibration, while the 276 cm^-1 vibration was a UO²⁺₂ deformation. The low values obtained for the force constant and totally symmetric stretching frequency of the U-O bond suggested that in UO₂(CO)^4-₃, the uranium atom is bound in a complex species that may be considered as an intermediate between that of a uranyl (UO²⁺₂) and a uranate (UO^10-₈) ion.     

Raman spectroscopic study of the multi‐anion mineral dixenite CuMn2+14Fe3+(AsO3)5(SiO4)2(AsO4)(OH)6

The mixed anion mineral dixenite has been studied by Raman spectroscopy, complemented with infrared spectroscopy. The Raman spectrum of dixenite shows bands at 839 and 813 cm⁻¹ assigned to the (AsO₃)³⁻ symmetric and antisymmetric stretching modes. The most intense Raman band of dixenite is the band at 526 cm⁻¹ and is assigned to the ν₂ AsO₃³⁻ bending mode. DFT calculations enabled the calculation of the position of AsO₂²⁻ symmetric stretching mode at 839 cm⁻¹, the antisymmetric stretching mode at 813 cm⁻¹, and the deformation mode at 449 cm⁻¹. The Raman bands at 1026 and 1057 cm⁻¹ are assigned to the SiO₄²⁻ symmetric stretching vibrations and those at 1349 and 1386 cm⁻¹ to the SiO₄²⁻ antisymmetric stretching vibrations. Both Raman and infrared spectra indicate the presence of water in the structure of dixenite. This brings into question the commonly accepted formula of dixenite as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆. The formula may be better written as CuMn²⁺₁₄Fe³⁺(AsO₃)₅(SiO₄)₂(AsO₄)(OH)₆·xH₂O. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl selenite mineral marthozite Cu[(UO2)3(SeO3)2O2]·8H2O

The mineral marthozite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 K. The bands at 812 and 797 cm⁻¹ were assigned to the symmetric stretching modes of the (UO₂)²⁺ and (SeO₃)²⁻ units, respectively. These values gave the calculated U O bond lengths in uranyl of 1.799 and/or 1.814 Å. Average U O bond length in uranyl is 1.795 Å, inferred from the X‐ray single crystal structure analysis of marthozite by Cooper and Hawthorne. The broad band at 869 cm⁻¹ was assigned to the ν₃ antisymmetric stretching mode of the (UO₂)²⁺ (calculated U O bond length 1.808 Å). The band at 739 cm⁻¹ was attributed to the ν₃ antisymmetric stretching vibration of the (SeO₃)²⁻ units. The ν₄ and the ν₂ vibrational modes of the (SeO₃)²⁻ units were observed at 424 and 473 cm⁻¹. Bands observed at 257, and 199 and 139 cm⁻¹ were assigned to OUO bending vibrations and lattice vibrations, respectively. O H···O hydrogen bond lengths were inferred using Libowiztky's empirical relation. The infrared spectrum of marthozite was studied for complementation. Copyright © 2008 John Wiley & Sons, Ltd.     

采用二维坐标和变分方法计算磷烷阳离子的伞型振动

提出一个新的二维变分方法计算PH₃⁺(X²A₂")的对称伸缩振动(v1)和伞形振动(v2). 因为采用了对称化的笛卡尔坐标,所以动能项变得简单,同时伞形振动模式也能得到很好的反映. 相比采用经常使用的一维模型计算伞形振动,这个二维模型不需要约化质量的假设,同时也考虑了v1和v2振动模式之间的相互作用. 用二维模型对PH₃⁺首次进行了计算, 前七个能级的理论值和实验值的平均相对误差小于3 cm^{-1. 用相同的方法也计算了NH₃,结果没有PH₃+理想,说明这个方法有一定的局限性.}     

High-resolution electron energy-loss spectroscopy of CO on an Ni(110) surface

High-resolution vibrational electron energy-loss spectra of CO on an Ni(110) surface were studied at 300 K with the in-situ combination of LEED, Auger electron spectroscopy and work-function change measurement. The observed peaks are at 436 cm^?1, 1855 cm^?1 (shifting to 1944 cm^?1 with increasing coverage) and at 1960 cm^?1 (shifting to 2016 cm^?1 with increasing coverage). The experimental results indicate that CO is adsorbed non-dissociatively at all coverages. Three adsorbed states of CO have been found. At fractional CO coverages less than θ ~ 0.9 where the disordered adsorbed structure dominates, CO is adsorbed in two inequivalent sites (short- and long-bridge sites) at random with its axis oriented perpendicular to the surface. At high coverages (θ > 0.9) where the (2 × 1) structure develops, our results indicate that the adsorbed CO molecules may occupy the distorted long-bridge sites forming zig-zag chains which lie essentially in the troughs of the (110) surface.     

Observation of a soft phonon in linear chain compound (NbSe4)3I by Raman scattering

The phase transition of the linear chain compound (NbSe₄)₃I was studied by Raman scattering. At 78 K three new peaks were observed at 73 cm^?1, 205 cm^?1 and 261 cm^?1. The totally symmetric Raman peak at 73 cm^?1 shows anomalous temperature dependence. The frequency decreases with increasing temperature, and at high temperatures an anticrossing occurs with another peak observed at about 58 cm^?1. The Raman intensity decreases and the linewidth broadens remarkably as the temperature increases. These properties allow us to assign this peak to a soft phonon. This fact indicates clearly the existence of a structural phase transition of a displacive type below room temperature.     

Schwingungsspektrum von Magnesiumsulfat-Heptahydrat (Epsomit) und Cäsiumsulfat

As in the preceding paper [1], infrared reflection spectra of single crystals of orthorhombic MgSO₄·7H₂O and MgSO₄·7D₂O have been obtained at 300°K, 80°K, and at about 14°K in the region between 4000 cm^?1 and 400 cm^?1. By a Kronig-Kramers analysis, the frequencies of the infrared active transitions have been determined. The spectra and their temperature dependence are contrasted with reflection spectra of anhydrous, orthorhombic Cs₂SO₄, which show practically no temperature dependence. The spectra of the magnesium compounds show two prominent features: 1. In the region below 700 cm^?1, the low-temperature experiments show the existence of many distinct vibrational modes arising mainly from the coupled translational and librational motions of the water molecules. These observations will be discussed in the light of the results of the preceding paper [1]. 2. The internal vibrations of the SO₄-ions at about 1100 cm^?1 present a very interesting combination of two solid-state effects on vibrational states of molecules in crystals: a) The threefold degeneracy of this mode is lifted by the deformation of the molecule due to the asymmetric crystal field, and b) the coupling of four molecules in the unit cell (resonance or correlation-field coupling) results in a further splitting of each mode into four clearly separated states of which three are infrared active. The magnitude of this splitting is calculated with the Davydov-theory (Coulomb-interaction of the transition-dipoles), making use of the crystal structure and the experimentally determined strength of the transition dipoles. Considering the limitation of the model, fairly good agreement with the experiment is obtained.