Microscopic structure of liquid dimethyl sulphoxide and its electrolyte solutions: molecular dynamics simulations

Molecular dynamics (MD) simulations of pure dimethyl sulphoxide (DMSO) and solutions of Na⁺, Ca²⁺, Cl^?, NaCl and CaCl₂ in DMSO have been performed at 298.15 K and 398.15 K in NVT ensembles by using a four-interaction-site model of DMSO and reaction field method for Coulombic interactions. The structure of solvent, ion-solvation shells and ion-pairs have been analysed by employing a concept of coordination centres and characteristic vectors of the solvent molecule. Results are given for atom-atom (corresponding to DMSO), ion-atom and ion-ion radial distribution functions (RDFs), orientation of the DMSO molecules and their geometrical arrangements in the first solvation shells of the ions (Na⁺, Ca²⁺, Cl^?). A preferential formation of cyclic dimers with antiparallel alignment between dipole moments of nearest-neighbour molecules in the pure solvent is found. Geometrical models of the first coordination shells of the ions in ‘infinitely dilute solutions’ are proposed. Ion-ion RDFs in NaCl-DMSO and CaCl₂-DMSO solutions reveal the presence of both solvent separated (SSIP) and contact (CIP) ion pairs. The structures of the solvation shells of such ion pairs are also discussed.     

Molecular dynamics simulations of carbon dioxide hydrate growth in electrolyte solutions of NaCl and MgCl2

Molecular dynamics simulations are performed to study the growth of carbon dioxide (CO₂) hydrate in electrolyte solutions of NaCl and MgCl₂. The kinetic behaviour of the hydrate growth is examined in terms of cage content, density profile, and mobility of ions and water molecules, and how these properties are influenced by added NaCl and MgCl₂. Our simulation results show that both NaCl and MgCl₂ inhibit the CO₂ hydrate growth. With a same mole concentration or ion density, MgCl₂ exhibits stronger inhibition on the growth of CO₂ hydrate than NaCl does. The growth rate of the CO₂ hydrate in NaCl and MgCl₂ solutions decreases slightly with increasing pressure. During the simulations, the Na⁺, Mg²⁺, and Cl^? ions are mostly excluded by the growing interface front. We find that these ions decrease the mobility of their surrounding water molecules, and thus reduce the opportunity for these water molecules to form cage-like clusters toward hydrate formation. We also note that during the growth processes, several 5¹²6³ cages appear at the hydrate/solution interface, although they are finally transformed to tetrakaidecahedral (5¹²6²) cages. Structural defects consisting of one water molecule trapped in a cage with its hydrogen atoms being attracted by two Cl^? ions have also been observed.     

First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO

ABSTRACT

A Fourier transform spectrum of phosgene (Cl₂CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm^?1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν₂ and ν₄ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 2¹ and 4¹ vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ～0.30 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν₀(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm^?1, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm^?1, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm^?1 and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm^?1.     

Effects of concentrated NaCl and KCl solutions on the behaviour of aqueous peptide bond environment: single-particle dynamics and H-bond structural relaxation

The effects of salt concentrations on the structure, dynamics and hydrogen bond structural relaxation properties of ～1.10 M aqueous N-methylacetamide (NMA) solution at 308 K are studied by classical molecular dynamics simulations. We have considered the concentration range of salts solution from 0.222 to 3.756 M to investigate the behaviour of aqueous environment of peptide bonds in the presence of concentrated NaCl and KCl solution. It is found that the addition of salt solution facilitates the structural breaking of aqueous NMA hydrogen bonds, as a result the number of hydrogen bonds per NMA molecule and their stability decreases. The water and NMA molecule shows slower translational and rotational dynamics with increasing salt concentrations due to additional ion atmospheric friction. Our result shows that the cation–O_NMA radial distribution function decreases whereas the Cl^?─H_NMA radial distribution function increases with ion concentration. On the other hand, the cation–O_water and Cl^?─H_water radial distribution function shows very negligible change with respect to ion concentration. We have also calculated NMA–water and water–water hydrogen bond structural relaxation times. It is observed that the hydrogen bond structural relaxation of O_NMA─H_water is comparatively slower than the H_NMA─O_water hydrogen bond, which can be attributed to higher number and greater stability of the former hydrogen bond than the latter. The change of the dynamical quantities observed here is more prominent in addition of NaCl rather than the KCl solution.     

Aggregation phenomena and dynamics in II-I and III-I hydrated molten salts

Summary We present results from EXAFS and Raman scattering on aqueous solutions on II-I and III-I salts. As II-I salt the system investigated was the ZnCl₂ and its mixture with LiCl, CaCl₂ and SrCl₂. It was shown that ZnCl₂ evidences a tetrahedral arrangement around the Zn²⁺ ion whereas Li⁺, Ca⁺ and Sr²⁺ ions prefer an inner-shell water complexation. In particular it was shown that the tetrahedral units become less and less interacting when the ratio Cl⁻/Zn²⁺ is increasing. Such structural results are confirmed by the Raman probe that shows the vibrational bands becoming more and more localized for Cl⁻/Zn²⁺ values higher than 2. For what III-I salts are concerned we report results on SbCl₃/H₂O mixture. EXAFS evidenciates an Sb−Cl and Sb...Cl coordination very close to that of pure SbCl₃. The water molecule appears linked to the chlorine giving rise to a cross-link between SbCl₃ chains. Raman confirms such a result showing that the C_3v symmetry of SbCl₃ molecule is lowered in the presence of water and shows a new chlorine-water contribution plus a phononlike contribution in the very lowfrequency region. Paper presented at the workshop ?Highlights on Simple Liquids?, held in Turin at ISI on 1–3 May, 1989.     

Ion-exchange of monovalent and bivalent cations with NaA zeolite membranes : a molecular dynamics study

Molecular simulations using the method of molecular dynamics have been carried out to study the dynamics and energetics of ion exchanges between monovalent and bivalent cations in supercritical and subcritical (liquid) electrolyte solutions (here Li⁺, and Ca⁺⁺ in aqueous solutions of LiCl and CaCl₂) and an ion exchange membrane (NaA zeolite) using direct simulations of up to a nanosecond or more. NaA zeolites are widely used in many commercial ion-exchange processes including detergents. Results show that with appropriate driving forces, such ion exchange processes can be clearly witnessed and investigated using molecular simulations at these timescales, especially for supercritical solutions. An attempt is made to understand the phenomenon of ion exchange at the molecular level. Results have shown that the ion-exchange process is primarily energetically driven and entropic forces do not appear to be playing a significant role in the exchanges observed. For supercritical LiCl solutions, small differences were found between the energy of the Li⁺ inside and outside the membrane. In contrast, for Na⁺ there was a considerable energetic advantage in being outside the membrane, making the overall exchange process energetically favourable. In subcritical (liquid) LiCl solutions an exchange was found to be more favourable energetically than supercritical solutions. For Ca⁺⁺ similar trends were observed, except the differences in the energies were much larger (compared to the corresponding Li⁺ exchanges), making them more energetically efficient, as has also been observed experimentally. In addition to clarifying the molecular basis for these exchanges, simulations can also potentially be very useful to determine the behaviour (e.g. state dependence, etc.) of hydrodynamic parameters commonly used to characterize ion-exchange processes at a fundamental molecular level, and to determine if the hydrodynamic equations used for ion-exchange processes are applicable to nano-systems that can be studied using simulations.     

Silicon negative ion implantation induced vacancy defects in thermally grown SiO2 thin films

ABSTRACT

Thermally grown SiO₂ thin films on a silicon substrate implanted with 100?keV silicon negative ions with fluences varying from 1?×?10¹⁵ to 2?×?10¹⁷ ions cm^?2 have been investigated using Electron spin resonance, Fourier transforms infrared and Photoluminescence techniques. ESR studies revealed the presence of non-bridging oxygen hole centers, E′-centers and P_b-centers at g-values 2.0087, 2.0052 and 2.0010, respectively. These vacancy defects were found to increase with respect to ion fluence. FTIR spectra showed rocking vibration mode, stretching mode, bending vibration mode, and asymmetrical stretching absorption bands at 460, 614, 800 and 1080?cm^?1, respectively. The concentrations of Si–O and Si–Si bonds estimated from the absorption spectra were found to vary between 11.95?×?10²¹ cm^?3 and 5.20?×?10²¹ cm^?3 and between 5.90?×?10²¹ cm^?3 and 3.90?×?10²¹ cm^?3, respectively with an increase in the ion fluence. PL studies revealed the presence of vacancies related to non-bridging oxygen hole centers, which caused the light emission at a wavelength of 720?nm.     

Infrared diode laser spectroscopy of the Kr–N2O van der Waals complex: the v 1 symmetric stretch region of N2O

The rovibrational spectra of four isotopomers of the Kr–N₂O van der Waals complex, namely ⁸²Kr–N₂O, ⁸³Kr–N₂O, ⁸⁴Kr–N₂O and ⁸⁶Kr–N₂O, were measured in the v ₁ vibrational band region of the N₂O monomer (～1285?cm^?1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. Rotational constants for both ground and excited vibrational states of these four isotopomers were accurately determined. The band-origin of Kr–N₂O was observed to shift by +0.1065?cm^?1 from that of the monomer. The band-origin shifts of Rg–N₂O (Rg?=?Ne, Ar, Kr) in the v ₁ vibrational band region could also be well explained by the model based on a Buckingham intermolecular potential [W.A. Herrebout, H.-B. Qian, H. Yamaguchi and B.J. Howard, J. Mol. Spectrosc. 189, 235 (1998)]. But the band-origin shift of He–N₂O was found to deviate significantly from this model. The possible reason is discussed and the band-origin shift of Xe–N₂O predicted.     

Exploration of large amplitude motions in the Ca+Ar2 complex

ABSTRACT

We present a theoretical study of the ground electronic state potential of the Ca⁺Ar₂ complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220?K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca⁺Ar₂ complex. Our study shows that the most stable form of Ca⁺Ar₂ is a bent C_2v structure, whereas the linear isomer is located at around 90?±?10?cm^?1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca⁺Ar₂ to linear ArCa⁺Ar occurs at T～100?K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures.     

High-resolution infrared and ab initio investigation of CHD2 79Br: Ro-vibrational analysis of the ν6 fundamental and the 2ν6−ν6 hot band

The high-resolution infrared spectrum of CHD₂ ⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 540–615?cm^?1 at an unapodised resolution of 0.0035?cm^?1. This spectral region is characterised by the ν₆ fundamental (584.8510?cm^?1), corresponding to C–Br stretching mode, and its hot band 2ν₆?ν₆ (578.4333?cm^?1). The spectral analysis resulted in the identification of 3430 transitions (J’?≤?73 and K'_a ?≤?18) for the ν₆ fundamental and 1212 transitions (J’?≤?49 and K'_a ?≤?11) for the hot band 2ν₆?ν₆. The assigned data have been fitted using the Watson’s S-reduced Hamiltonian in the I^r representation and new constants for the ground state from about 24,600 combination differences and sets of parameters for the v ₆?=?1 and 2 vibrational states have been obtained. From spectral simulations the intensity ratio between 2ν₆?ν₆ and ν₆ has been estimated to be 0.15?±?0.02. High-quality ab initio calculations have also been performed at the CCSD(T) level of theory in order to support the experimental investigation through the calculation of molecular parameters relevant to ro-vibrational spectroscopy.     

Hydrogen bonds at silica–CO2 saturated water interface under geologic sequestration conditions

To investigate the effects of sequestration condition on hydrogen bonds between mineral and water, molecular dynamics simulations have been performed. The simulations were conducted at conditions related with geologic sequestration sites: pressure (3.1–32.6 MPa), temperature (318 and 383 K), salinity (0–3 M), salt (NaCl and CaCl₂) and silica surface models Q² (geminal), Q³ (isolated) and amorphous Q³. The hydrogen bonds were classified into four types: silica–silica, silica–dissolved CO₂, silica–water as donors and silica–water as acceptors. The mean numbers of hydrogen bonds for each type were analysed. The results show that: (1) silica surface silanol groups do not form H-bonds with dissolved CO₂ molecules in water (brine); (2) The mean number of hydrogen bonds between silanol groups follows the order: Q² > amorphous Q³ > Q³; (3) The mean number of hydrogen bonds between silanol and water molecules follows the order: Q³ > amorphous Q³ > Q².     

Comparison of Inductively Coupled Plasma with Classical Analytical Techniques in the Analysis of Southern Oregon Lithia Water: Inclusion of a Local Resource in the Undergraduate Chemistry Curriculum

Abstract

Lithia water, a community resource of local historical significance, is described as a central theme in the undergraduate analytical chemistry sequence. A statistical comparison of the classical determination of major cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (HCO₃ ^?, Cl^?) reinforces statistical and charge‐balance concepts covered in analytical chemistry. Subsequent determination of these major cations by inductively coupled plasma (ICP) enables students to statistically evaluate the presence of bias between instrumental and classical methods. The effect of easily ionized elements on ICP calibration sensitivity and linearity via the use of cesium as an ionization suppressor is reported.     

Phase transitions and energy storage properties of some compositions in the (1−x)Li2SO4–xNa2SO4 system

In the binary system (1?x)Li₂SO₄–xNa₂SO₄, the solid–solid phase transitions and energy storage properties of Li₂SO₄, Na₂SO₄, the binary compound LiNaSO₄ and two eutectoids (E₁: 0.726Li₂SO₄–0.274Na₂SO₄; E₂: 0.03Li₂SO₄–0.97Na₂SO₄) were investigated by X-ray diffraction and differential scanning calorimetry. Li₂SO₄ has a solid–solid phase transition at 578 °C with the transition enthalpy 252 J g^?1. The binary compound LiNaSO₄ gives a slightly lower enthalpy value, 214 J g^?1 and its transition temperature is clearly reduced to 514 °C. The transition enthalpy of the eutectoid E₁ is maintained to 177 J g^?1 and its transition temperature is further reduced to 474 °C. Li₂SO₄, LiNaSO₄ and the eutectoid E₁ are applicable phase transition materials because of their large transition enthalpies. The enthalpies of Na₂SO₄ and the eutectoid E₂ are not very high (～45 J g^?1), but their transition temperatures are quite low (～250 °C); thus their transition properties may be applied at such low temperatures.     

Optical properties and the crystal structure of anhydrous gadolinium-trichloride

The Raman and i.r. reflection spectra of GdCl₃ have been studied in order to estabish the optically active fundamental frequencies. Gd³⁺?Cl^?)-and (Cl^??Cl^?)-force constants in GdCl₃ and in LaCl₃ and PrCl₃ have been calculated on the basis of a simple rigid ion model. It is found that the apparently anomalous spectra of GdCl₃ may be a result of a stronger (Cl^??Cl^?)-coupling constant than in the hexagonal rare earth trichlorides with lower Z on the metal ion. This peculiar status of GdCl₃ is related to the change of crystal structure in the series of Rare-Earth trichlorides from a hexagonal (La-…Gd-) Cl₃ to an orthorhombic (TbCl₃ DyCl₃) structure. Some properties of the electronic spectra are also discussed in this context.     

Swift ion irradiation effect on high-k ZrO2- and Al2O3-based MOS devices

This paper describes the heavy ion-induced effects on the electrical characteristics of reactively sputtered ZrO₂ and Al₂O₃ high-k gate oxides deposited in argon plus nitrogen containing plasma. Radiation-induced degradation of sputtered high-k dielectric ZrO₂/Si and Al₂O₃/Si interface was studied using 45?MeV Li³⁺ ions. The devices were irradiated with Li³⁺ ions at various fluences ranging from 5?×?10⁹ to 5?×?10¹²?ions/cm². Capacitance–voltage and current–voltage characteristics were used for electrical characterization. Shift in flat band voltage towards negative value was observed in devices after exposure to ion radiation. Post-deposition annealing effect on the electrical behavior of high-k/Si interface was also investigated. The annealed devices showed better electrical and reliability characteristics. Different device parameters such as flat band voltage, leakage current, interface defect density and oxide-trapped charge have been extracted.The surface morphology and roughness values for films deposited in nitrogen containing plasma before and after ion radiation are extracted from Atomic Force Microscopy.     

Synthesis and luminescence properties of green phosphors Ca6Sr4(Si2O7)3Cl2:Eu2+ for white light emitting diodes

Divalent europium-activated chlorosilicate Ca₆Sr₄(Si₂O₇)₃Cl₂:Eu²⁺ phosphors were synthesized by a conventional solid-state reaction under reductive atmosphere. These phosphors can be efficiently excited by UV–visible light from 320 to 420 nm, which matches that of a near UV-emitting InGaN chip. Under the 360 nm excitation, Ca₆Sr_3.97(Si₂O₇)₃Cl₂:0.03Eu²⁺ phosphor shows a strong and broad emission centering at 515 nm, which is attributed to the 5d→4f transition of Eu²⁺ ion. The mechanism of concentration quenching was determined to be the dipole–dipole interaction and the critical energy-transfer distance of Eu²⁺ was calculated as 3.31 nm. The CIE chromaticity coordinates of Ca₆Sr_3.96(Si₂O₇)₃Cl₂:0.03Eu²⁺ phosphor are (0.127, 0.770) according to the emission spectrum. It can be expected that Ca₆Sr₄(Si₂O₇)₃Cl₂:Eu²⁺ phosphor is a promising candidate as the green component for near-ultraviolet InGaN-based white LED.     

Equilibrium molecular dynamics calculation of the bulk viscosity of liquid water

Twenty independent equilibrium molecular dynamics simulations were performed in NVE ensemble to calculate the bulk viscosity of water at a temperature of 303 K and a density of 0.999 gcm^?3. The energy of each simulation with a production time of 200ps was conserved within 1 part in 10⁴. By stopping the velocity-scaling procedure at a proper step, the energies of independent simulations were specified precisely. This caused the simulations of different start configurations to sample the same NVE ensemble. The shear viscosity of SPC/E water obtained in the present study was 6.5±0.4 × 10^?4 Pas, which is in close agreement with a previous calculation in the NVT ensemble (Balasubramanian, S., Mundy, C. J., and Klein, M. L., 1996, J. clzern. Phys., 105, 11 190). The bulk viscosity was 15.5 ± 1.6 × 10^?4 Pas, which is 27% smaller than the experimental value. Thus, like its behaviour in predicting the shear viscosity, the SPC/E model also underestimates the bulk viscosity of real water.     

Preparation of Sm3+–Eu3+ coactivating red-emitting phosphors and improvement of their luminescent properties by charge compensation

By charge compensating, a series of red-emitting phosphors Ca_0.54Sr_0.16Ca_0.54Sr_0.31Eu_0.08Sm_0.02(MoO₄)_0.6(WO₄)_0.4 were synthesized. Two approaches to charge compensation were used: (a) 2Ca²⁺/Sr²⁺→Eu ³⁺/Sm³⁺+M ⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ or K⁺; (b) Ca²⁺/Sr²⁺→Eu ³⁺/Sm³⁺+N ^?, where N⁺ is a monovalent anion like F^?, Cl^?, Br^?, or I^?. One red LED was made by combining the phosphor and 390–405 nm emitting LED chip under 20 mA forward-bias current, the color purity, chromaticity coordinates and the luminous intensity of which were 99.5%, x=0.66, y=0.33, 5600 mcd, respectively.     

Laser-induced voltage effects in Ca3Co4O9 thin films on tilted LaAlO3（001） substrates grown by chemical solution deposition

Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10 tilted LaAlO3(001) substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, open-circuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.     

High-pressure in-situ X-ray diffraction and Raman spectroscopy of Ca2AlFeO5 brownmillerite

The behavior of Ca₂AlFeO₅ brownmillerite was studied by in situ synchrotron X-ray diffraction and Raman spectroscopy at 300?K with pressures up to 26.5 and 32.1 GPa, respectively. A reversible structural phase transition was observed. The P–V data were fitted by a third-order Birch–Murnaghan equation of state, and the isothermal bulk modulus was obtained as K₀?=?181.9(76) GPa with K₀′_?=?4.4(17). If K₀′ was fixed to 4, K₀ was obtained as 183.8(20) GPa. Ca₂AlFeO₅ brownmillerite shows an axial elastic anisotropy since the b-axis is more compressible than a- and c-axis. Combined with previous results, the isothermal bulk modulus and axial compressibility of Ca₂AlFeO₅ brownmillerite increase with more Al incorporated in the structure. The Raman spectra of Ca₂AlFeO₅ brownmillerite were analyzed and the pressure coefficients vary from 2.23 to 4.90?cm^?1/GPa. The isothermal mode Grüneisen parameters range from 0.83 to 1.77 and the thermal Grüneisen parameter is determined as 1.08(11).