Vibrational spectroscopy of SnBr4 and CCl4 using Lie algebraic approach

The stretching and bending vibrational energies of SnBr₄ and CCl₄ are calculated in the one-dimensional framework. The dynamical symmetry group of tetrahedral molecule was taken into consideration to construct the model Hamiltonian in this framework. Casimir and Majorana invariant operators were also determined accordingly. Using the model Hamiltonian so constructed, we reported the vibrational energy levels of SnBr₄ and CCl₄ molecules accurately.      

Collision-induced simultaneous transitions in H2+CF4 and H2+SF6 mixtures

The simultaneous transitions of the v₃ fundamental vibrations of CF₄ and SF₆ with the fundamental Q branch and S(1) line of H₂ have been studied for various H₂+CF₄ and H₂+SF₆ mixtures at total pressures up to 185 bars. The integrated intensities are found to be proportional to the partial densities of the gas mixture components. The agreement between experimental and calculated intensities is generally better for the Kihara potential than for the Lennard-Jones potential.     

Vibrational study of H3OUO2PO4·3 H2O (HUP) and related compounds. Phase transitions and conductivity mechanism: Part II,H3OUO2PO4·3 H2O

Infrared and Raman spectra of polycrystalline H₃OUO₂PO₄·3 H₂O (HUP) and its D and P¹⁸O₄ derivatives, in the form of dense transparent disks and wet powder, have been investigated at various temperatures in the 100–300 K region. The bands due to framework vibrations are similar to those of KUP, whereas those for the protonic species are different. OH stretching and bending bands of the oxonium ion have been identified at 2920, 1740 and 1160 cm^?1 in the low-temperature spectrum of HUP. Differential scanning calorimetry (DSC) and infrared (IR) intensity investigations show a phase transition between 274 and 260 K. The mechanism of the phase transition consists, as in the case of KUP, of ordering of the protonic species, which induces ordering of PO₄ tetrahedra. The ordering can be influenced by excess water content, stacking faults and stress (ferroelastic behaviour is evidenced). The conductivity mechanism in HUP is discussed.     

Magnetic phase diagram of MnBr24H2O

The magnetic phase diagram of the monoclinic antiferromagnet MnBr₂4H₂O (obtained from differential magnetization measurements) is presented for temperatures down to T = 0.3 K, and for applied magnetic fields parallel to the crystallographic axes a', b and c. For H∥c an unusual behaviour is observed below T ≈ 0.55 K where the antiferro-paramagnetic boundary apparently splits into three others. It is shown that our critical fields extrapolated to T = 0 are consistent with a recent theory proposed by Becerra and Ferreira.     

Vibrational study of phase transitions and conductivity mechanism in H3OUO2PO4.3 H2O (HUP)

Infrared and Raman spectra of polycrystalline H₃OUO₂PO₄.3 H₂O (HUP) have been envestigated at various temperatures between 50 K and 300 K. The most temperature sensitive bands corresponding to PO₄ and H₂O librations, U-OPO₃ stretching and OH stretching vibrations indicate four different phases of HUP and allow to propose a phase transition mechanism from a quasiliquid state of protonated species in R.T. phase to a fully ordered crystal below 100 K. Protonic conductivity mechanism of room and low temperature phases is discussed.     

Vibrational study of H3OUO2PO4 · 3 H2O (HUP) and related compounds. phase transitions and conductivity mechanisms: part I,KUO2PO4 · 3 H2O (KUP)

Infrared and Raman spectra of polycrystalline KUO₂PO₄ · 3 H₂O (KUP) and its isotopic derivatives KUO₂P¹⁸O₄ · 3 H₂O and KUO₂PO₄ · 3 D₂O have been investigated in the 4000-10-cm^?1 range at different temperatures. An assignment of the bands in terms of UO₂, PO₄ and H₂O vibrations has been proposed. Combined differential scanning calorimetry and spectroscopic data show two diffuse phase transitions near 130 and 230 K. Comparison of the vibrational spectra of phase I at 300 K and phase IV at 100 K indicates that ordering of the water molecules with subsequent ordering of PO₄ tetrahedra on a site with lower symmetry appears to be the main mechanism responsible for the phase transformation. All the six O-H distances of water molecules in phase IV are found to be crystallographically nonequivalent. Conducting ion frequencies and the corresponding force constants have been determined for the analogous compounds MUP with M = K⁺, Na⁺, Ag⁺, NH⁺₄, Tl⁺ and H₃O⁺ and compared with other properties of these ionic conductors. Conductivity mechanisms in these materials are discussed.     

Optical absorption spectra of Nd2(SO4)38H2O complexes in solution

The values of Slater-Condon, spin-orbit, Racah, and Judd-Ofelt intensity parameters are reported. Observed energy levels and spectral intensities have been correlated with theoretically computed values. The nature of bonding in Nd³⁺ complexes is discussed. The oscillator strength of the hypersensitive transition decreases with a decrease of the Judd-Ofelt T₂ parameter.     

Proton magnetic resonance in CoHgCl4· 4H2O

Proton magnetic resonance in a new paramagnetic crystalline hydrate, cobalt mercuric chloride tetrahydrate, was observed using a CW wide line NMR spectrometer. The resonance spectra showed appreciable asymmetry caused by the paramagnetic influence of Co²⁺ ions at the proton sites. The angular dependence of the resonance splittings about each of the three crystallographic axes was analysed to determine the p-p vectors in the unit cell of the crystal, and the angular variation of paramagnetic shift about the [001] axis of rotation was studied.     

Absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O

Optical absorption spectra of Ni²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O and Co²⁺ in Na₂Zn(SO₄)₂·4H₂O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band in Ni²⁺ and ${}^4\text{T}{}_{\mathrm{2g}}\text{(F)}$ band in Co²⁺ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm^-1 in the case of Ni²⁺ at low temperature has been interpreted to be the superposition of vibrational mode of SO^2-₄ radical on ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.     

Vibrational spectra of crystalline H2SeO3 in the O-H stretching region

IR transmission, near-normal IR reflection and polarized Raman spectra of single crystals of selenious acid (H₂SeO₃) have been obtained at temperatures between 77°K and 335°K. The observed bands in the O-H stretching region have been assigned to two types of O-H….O bonds in the crystal structure. The spectral results appear to rule out correlation field splittings, intramolecular coupling, or Fermi resonance as explanations for the observed splitting. A proposed model based on intermolecular coupling of O-H….O vibrations to explain the splitting of the O-H stretching region is given.     

Aimantation a basse temperature de deux sels ferromagnetiques uniaxes. Cu(NH4)2Br4, 2H2O ET CuRb2Br4, 2H2O

The low temperature spontaneous magnetization of the spin 1/2 b.c.c. ferromagnet has been computed using the self-consistently renormalized spin-wave theory of Bloch, taking into account weakly anisotropic exchange. A good agreement with our experimental data in Cu(NH₄)₂Br₄, 2H₂O and CuRb₂Br₄, 2H₂O is observed for 0 < T/T_{c < 0.5}, using the following anisotropy fields at 0°K: (293 ± 25) oe in Cu(NH₄)₂Br₄, 2H₂O and (300 ± 25)oe in CuRb₂Br₄, 2H₂O.     

A calorimetric study of LiClO4 · 3H2O

The heat capacity of LiClO₄ · 3H₂O was measured from 17 to 343 K, in order to determine the relationship between its phase diagram and the phase diagrams of divalent metal perchlorate hexahydrates The heat capacity curve of pure LiClO₄ · 3H₂O was found to be smooth, indicating an absence of polymorphism, although a small amount of excess perchloric acid in one sample gave rise to a eutectic point at 232 8 ± 0 3 K The absence of transitions in LiClO₄ · 3H₂O is discussed in terms of its known structure, and some conclusions are drawn concerning the differences in H-bonding in this salt and in divalent metal perchlorate hexahydrates.     

Penning ionization electron spectroscopy of H2O,D2O,H2S and SO2

Electron energy peak shifts and peak shapes were determined in the ionization of H₂O, D₂O, H₂S and SO₂ by Ne(³P₂) and He(2¹S, 2³S) metastable atoms. The shifts are large, especially in ionization of H₂O and D₂O into the ionic ground state and are probably mostly due to chemical interaction during the collision.In a previous paper the electron energy distribution curves for ionization of CO, HCl, HBr, N₂O, NO₂, CO₂, COS and CS₂ by helium, neon and argon metastables and the characteristics of this ionization were described¹. In this paper the series of triatomic molecules was extended to the molecules H₂O, D₂O, H₂S and SO₂. Because all these molecules have considerable dipole moments it could be expected that the peak shifts might be enhanced as compared with other triatomic molecules.     

High-resolution infrared spectra of water vapor ν2 band of H2O

The ν₂ band of H₂¹⁸O occurring in the region 5–7.5 μ was recorded with a high-resolution vacuum infrared spectrograph and an analysis was presented of the rotational structure observed; comparison of the ground state (000) energy levels determined from the ν₂ band with those derived earlier by Fraley, Rao, and Jones from the ν₁ and ν₂ bands at 2.7 μ was of assistance in this analysis. Values for the energy levels of the first excited state (010) were evaluated.     

Elucidating surface properties of dry-etched ZnO using H2/CH4 and H2/CH4/Ar plasma

This paper reports a study of reactive ion etching (RIE) of n-ZnO in H₂/CH₄ and H₂/CH₄/Ar gas mixtures. Variables in the experiment were gas flow ratios, radio-frequency (rf) plasma power, and total pressure. Structural and electrical parameters of the etched surfaces and films were determined. Both the highest surface roughness and highest etching rate of ZnO films were obtained with a maximum rf power of 300 W, but at different gas flow ratios and working pressures. These results were expected because increasing the rf power increased the bond-breaking efficiency of ZnO. The highest degree of surface roughness was a result of pure physical etching by H₂ gas without mixed CH₄ gas. The highest etching rate was obtained from physical etching of H₂/Ar species associated with chemical reaction of CH₄ species. Additionally, the H₂/CH₄/Ar plasma treatment drastically decreased the specific contact and sheet resistance of the ZnO films. These results indicated that etching the ZnO film had roughened the surface and reduced its resistivity to ohmic contact, supporting the application of a roughened transparent contact layer (TCL) in light-emitting diodes (LEDs).     

Collisional broadening and shifting of the 211-202 transition of H2O, H2O, H2O by atmosphere gases

Broadening and shifting of the 2₁₁-2₀₂ transition of H₂¹⁶O, H₂¹⁷O, H₂¹⁸O by pressure of water, nitrogen and oxygen were precisely measured at room temperature using spectrometer with radio-acoustic detection of absorption. Shift parameters for all studied lines as well as broadening parameters of H₂¹⁷O, H₂¹⁸O lines were measured for the first time. Comparison of obtained results with previously known experimental and theoretical data is presented.     

Protonic conductivity of solid UO2HPO4·3H2O

The electrical and electrochemical properties of the solid ionic conductor UO₂HPO₄·3H₂O were investigated within the temperature range from room temperature up to 673 K. The conductivity of a nondehydrated sample within the temperature range from 303 K (6.5 × 10^-3 S/m) to 350 K (2.5 × 10^-2 S/m), with the activation energy of 23 kJ/mol, is a consequence of the presence of crystal water, and originates, mostly, from the fast movement of protons across the network of molecules of water in a tunneling mechanism pattern. When heated, the conductor loses crystal water, which leads to a final change in the nature of the conductor and in the conductivity mechanism. The conductivity of the dehydrated salt UO₂HPO₄ (2.5 × 10^-4 S/m at 488 K), with the activation energy 44.04 kJ/mol, is considerably lower than the one mentioned above and can be attributed, to a great extent, to the movement of protons, most likely by a tunneling mechanism, through the less favourable structure formed by phosphate groups of the dehydrated salt. On being heated above 623 K for a certain time, the acid phosphate transforms into pyrophosphate, the conductivity of which is lower than that mentioned above. By means of electrochemical methods, the electrode processes were studied. It has been shown that H⁺ and UO²⁺ ions are reduced at the cathode, while the phosphate groups oxidize at the anode and O₂ is evolved.     

Absorption spectra of vanadyl ion doped in MgNH4PO4·6H2O (struvite) crystal

Results of Electron Paramagnetic Resonance (EPR) and optical absorption studies of VO²⁺ ion doped in struvite at room liquid nitrogen temperatures are reported. Three preferential V=O bond directions in the crystal have been identified. The optical and EPR data have shown the formation of NH₄(PO₄VO(H₂O)₅ complex in the crystal as a result of VO²⁺ doping. Correlating the optical and EPR data the molecular orbital coefficients are also obtained and discussed.