Showing papers by "Environmental Molecular Sciences Laboratory published in 2003"
TL;DR: In this article, the density functional theory was applied to representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, using density functional analysis.
Abstract: Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations ...
1,061 citations
TL;DR: Using relativistic density functional calculations, it is found that Au20 possesses a tetrahedral structure, which is a fragment of the face-centered cubic lattice of bulk gold with a small structural relaxation, which suggests that the Au20 cluster should be highly stable and chemically inert.
Abstract: Photoelectron spectroscopy revealed that a 20-atom gold cluster has an extremely large energy gap, which is even greater than that of C60, and an electron affinity comparable with that of C60. This observation suggests that the Au20 cluster should be highly stable and chemically inert. Using relativistic density functional calculations, we found that Au20 possesses a tetrahedral structure, which is a fragment of the face-centered cubic lattice of bulk gold with a small structural relaxation. Au20 is thus a unique molecule with atomic packing similar to that of bulk gold but with very different properties.
1,006 citations
TL;DR: Experimental and theoretical evidence is reported that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the Hückel rules, akin to planar hydrocarbons.
Abstract: An interesting feature of elemental boron and boron compounds is the occurrence of highly symmetric icosahedral clusters. The rich chemistry of boron is also dominated by three-dimensional cage structures. Despite its proximity to carbon in the periodic table, elemental boron clusters have been scarcely studied experimentally and their structures and chemical bonding have not been fully elucidated. Here we report experimental and theoretical evidence that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the Huckel rules, akin to planar hydrocarbons. Aromatic boron clusters possess more circular shapes whereas antiaromatic boron clusters are elongated, analogous to structural distortions of antiaromatic hydrocarbons. The planar boron clusters are thus the only series of molecules other than the hydrocarbons to exhibit size-dependent aromatic and antiaromatic behaviour and represent a new dimension of boron chemistry. The stable aromatic boron clusters may exhibit similar chemistries to that of benzene, such as forming sandwich-type metal compounds.
589 citations
TL;DR: Experimental and theoretical evidence is reported that 8- and 9-atom boron clusters are perfectly planar molecular wheels, with a hepta- or octacoordinated central borons atom, respectively, despite the predominance of three-dimensional structures normally found in bulk bor on and its compounds.
Abstract: Clusters of atoms can adopt different atomic arrangements from bulk materials. They often exhibit novel structures and properties, which provide opportunities for a new types of chemical bonding and stoichiometry. Herein we report experimental and theoretical evidence that 8- and 9-atom boron clusters are perfectly planar molecular wheels, with a hepta- or octacoordinated central boron atom, respectively, despite the predominance of three-dimensional structures normally found in bulk boron and its compounds.
447 citations
TL;DR: In this article, it was shown that molecular oxygen reacts with bridging OH (OHbr) groups formed as a result of water dissociation at oxygen vacancy defects on the surface of rutile TiO2(110).
Abstract: In this study we show that molecular oxygen reacts with bridging OH (OHbr) groups formed as a result of water dissociation at oxygen vacancy defects on the surface of rutile TiO2(110). The electron...
393 citations
TL;DR: A symbolic manipulation program and program generator (tensor contraction engine or TCE) that abstracts and automates the time-consuming, error-prone processes of deriving theensor contraction engines.
Abstract: We have developed a symbolic manipulation program and program generator (tensor contraction engine or TCE) that abstracts and automates the time-consuming, error-prone processes of deriving the wor...
388 citations
TL;DR: In this paper, the surface chemistry of water on the oxidized and reduced surfaces of a 500 A epitaxial CeO 2 (1/2 4f 0) film grown on yttria-stabilized ZrO 2 was investigated.
380 citations
TL;DR: In this article, the interaction of water and methanol with well-defined (1 × 1) terminated surfaces of anatase-TiO2(101) was investigated with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS).
Abstract: The interaction of water and methanol with well-defined (1 × 1) terminated surfaces of anatase-TiO2(101) were investigated with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). For water, three desorption states were observed in the TPD spectra at 160, 190, and 250 K. The three desorption peaks were assigned to multilayer water, water adsorbed to 2-fold-coordinated O, and water adsorbed to 5-fold-coordinated Ti, respectively. The TPD spectra for methanol were more complicated. For methanol, five desorption peaks were observed in the TPD spectra at 135, 170, 260, 410, and 610 K. The five desorption peaks were assigned to multilayer methanol, methanol adsorbed to 2-fold-coordinated O, methanol adsorbed to 5-fold-coordinated Ti, methoxy adsorbed to 5-fold-coordinated Ti, and methoxy adsorbed to Ti at step edges, respectively. The XPS results indicated that the adsorbed water and methanol were predominantly bound to the surface in a molecular state, with no evidence for diss...
359 citations
TL;DR: A comparison of published calcite dissolution rates measured far from equilibrium at a pH of ∼ 6 and above shows well over an order of magnitude in variation Recently published AFM step velocities extend this range further still.
319 citations
TL;DR: Experimental and theoretical characterization of antiaromaticity in an all-metal system, Li3Al4–, produced by laser vaporization and studied with the use of photoelectron spectroscopy and ab initio calculations reveal a rectangular Al44– tetraanion stabilized by the three Li+ ions in a capped octahedral arrangement.
Abstract: We report the experimental and theoretical characterization of antiaromaticity in an all-metal system, Li3Al4–, which we produced by laser vaporization and studied with the use of photoelectron spectroscopy and ab initio calculations. The most stable structure of Li3Al4– found theoretically contained a rectangular Al44– tetraanion stabilized by the three Li+ ions in a capped octahedral arrangement. Molecular orbital analyses reveal that the rectangular Al44– tetraanion has four π electrons, consistent with the 4n Huckel rule for antiaromaticity.
211 citations
TL;DR: Amorphous helical SiO2 nanosprings were synthesized with a chemical vapor deposition technique, characterized and manipulated by scanning (SEM) and transmission (TEM) electron microscopy and atomic force microscopy (AFM).
Abstract: Amorphous helical SiO2 nanosprings (80 to 140 nm in diameter and up to 8 microns long) were synthesized with a chemical vapor deposition technique, characterized and manipulated by scanning (SEM) and transmission (TEM) electron microscopy and atomic force microscopy (AFM). The helical nanosprings were observed in the middle of a straight nanowire and were formed by a perturbation during the growth of the straight nanowire. Contraction and expansion of the helical nanosprings were observed under in situ electron beam heating during TEM, as well as bending induced by an AFM tip, suggesting that the helical nanosprings are highly flexible and may have potential applications in nanomechanical, nanoelectronmagnetic devices, and composite materials.
TL;DR: In this paper, a rapid and clean approach was developed to synthesize metal nanowires and nanorods using multi-walled carbon nanotubes (MWCNTs) as templates and supercritical CO{sub 2} as the reaction medium.
Abstract: A rapid, direct and clean approach has been developed to synthesize metal (Pd, Ni and Cu) nanowires and nanorods using multi-walled carbon nanotubes (MWCNTs) as templates and supercritical CO{sub 2} as the reaction medium. Filling of metals into MWCNTs to form nanowires or nanorods was easily achieved by the simple hydrogen reduction of metal-b-diketone complexes in supercritical CO{sub 2}.
TL;DR: The ability to quantify differences in protein expression and post-translational modifications using stable isotope labeling has been achieved, but insights into the biochemical mechanisms that will contribute to the development of new biotechnologies have yet to be realized.
TL;DR: Pd(II)-beta-diketone precursor in supercritical carbon dioxide produces palladium nanoparticles on multi-walled carbon nanotubes that exhibit promising catalytic properties for hydrogenation of olefins in carbon dioxide as well as electro-reduction of oxygen in fuel cell applications.
TL;DR: In this paper, the atomic structure of dioctahedral 2:1 phyllosilicate edge surfaces was calculated using pseudopotential planewave density functional theory, and it was shown that significant surface relaxation should occur on the (110)-type faces, as well as in response to different protonation schemes on both surface types.
Abstract: The atomic structure of dioctahedral 2:1 phyllosilicate edge surfaces was calculated using pseudopotential planewave density functional theory. Bulk structures of pyrophyllite and ferripyrophyllite were optimized using periodic boundary conditions, after which crystal chemical methods were used to obtain initial terminations for ideal (110)- and (010)-type edge surfaces. The edge surfaces were protonated using various schemes to neutralize the surface charge, and total minimized energies were compared to identify which schemes are the most energetically favorable. The calculations show that significant surface relaxation should occur on the (110)-type faces, as well as in response to different protonation schemes on both surface types. This result is consistent with atomic force microscopy observations of phyllosilicate dissolution behavior. Bond-valence methods incorporating bond lengths from calculated structures can be used to predict intrinsic acidity constants for surface functional groups on (110)- and (010)-type edge surfaces. However, the occurrence of surface relaxation poses problems for applying current bond-valence methods. An alternative method is proposed that considers bond relaxation, and accounts for the energetics of various protonation schemes on phyllosilicate edges.
TL;DR: In this paper, the phase transformation of solid particles into liquid droplets through heterogeneous chemistry was shown in a two-step mechanism involving the conversion of calcium carbonate into calcium nitrate followed by the deliquescence of the calcium Nitrate product.
Abstract: [1] Individual calcium carbonate particles reacted with gas-phase nitric acid at 293 K have been followed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX) analysis as a function of time and relative humidity (RH). The rate of calcium carbonate to calcium nitrate conversion is significantly enhanced in the presence of water vapor. The SEM images clearly show that solid CaCO 3 particles are converted to spherical droplets as the reaction proceeds. The process occurs through a two-step mechanism involving the conversion of calcium carbonate into calcium nitrate followed by the deliquescence of the calcium nitrate product. The change in phase of the particles and the significant reactivity of nitric acid and CaCO 3 at low RH are a direct result of the deliquescence of the product at low RH. This is the first laboratory study to show the phase transformation of solid particles into liquid droplets through heterogeneous chemistry.
TL;DR: In this paper, the structure of α-Fe2O3 (001) surfaces is not fully understood, and questions have arisen recently concerning different terminations of (1) terraces; a so-called Fe-termination is expected, but under some conditions an O-termination may also be possible.
TL;DR: The relationship between the free energy of activation and the potential of mean force is derived for reaction coordinates that are arbitrary functions of all the coordinates defining a system in this paper, and the general result is illustrated for rectilinear reaction coordinates, bond distance reaction coordinates and energy gap reaction coordinates.
Abstract: The relationship between the free energy of activation and the potential of mean force is derived for reaction coordinates that are arbitrary functions of all the coordinates defining a system. The general result is illustrated for rectilinear reaction coordinates, bond distance reaction coordinates, atom transfer reaction coordinates, synchronous double atom transfer reaction coordinates, and energy gap reaction coordinates.
TL;DR: The first CaP coatings were produced via vapor phase processes, but more recently solution-based and biomimetic methods have emerged as mentioned in this paper, which promise to improve implant biocompatibility and ultimately implant longevity.
TL;DR: An improved stable-isotope labeling method using a phosphoprotein isotope-coded solid-phase tag (PhIST) for isolating and measuring the relative abundances of phosphorylated peptides from complex peptide mixtures resulting from the enzymatic digestion of extracted proteins.
Abstract: Many cellular processes are regulated by reversible protein phosphorylation, and the ability to broadly identify and quantify phosphoproteins from proteomes would provide a basis for gaining a better understanding of these dynamic cellular processes. However, such a sensitive, efficient, and global method capable of addressing the phosphoproteome has yet to be developed. Here we describe an improved stable-isotope labeling method using a phosphoprotein isotope-coded solid-phase tag (PhIST) for isolating and measuring the relative abundances of phosphorylated peptides from complex peptide mixtures resulting from the enzymatic digestion of extracted proteins. The PhIST approach is an extension of the previously reported phosphoprotein isotope-coded affinity tag (PhIAT) approach developed by our laboratory,1,2 where phosphoseryl and phosphothreonyl residues were derivatized by hydroxide ion-mediated β-elimination followed by the Michael addition of 1,2-ethanedithiol (EDT). Instead of using the biotin affinit...
TL;DR: This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center, as well as four distinct CUO(Ar)(4-n)(Ng)(n) complexes.
Abstract: Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies (12C16O, 13C16O, 12C18O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)4-n(Ng)n (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas−actinide complexes, and the first example of neutral complexes with four n...
TL;DR: In this article, a self-contained asymptotic correction to exchange-correlation potentials in Kohn−Sham density functional theory (DFT) for use in time-dependent DFT was proposed.
Abstract: By combining the asymptotic correction scheme of Casida and Salahub for exchange-correlation potentials and the phenomenological linear correlation between experimental ionization potentials and highest occupied Kohn−Sham (KS) orbital energies found by Zhan, Nichols, and Dixon, we propose a new, expedient, and self-contained asymptotic correction to exchange-correlation potentials in KS density functional theory (DFT) for use in time-dependent density functional theory (TDDFT) that does not require an ionization potential as an external parameter from a separate calculation. The asymptotically corrected (TD)DFT method is implemented in the quantum chemistry program suite NWChem for both sequential and massively parallel execution. The asymptotic correction scheme combined with the B3LYP functional [B3LYP(AC)] is shown to be well balanced for both valence- and Rydberg-type transitions, with average errors in excitation energies of CO, N2, CH2O, and C2H4 being smaller than those of uncorrected BLYP and B3LY...
TL;DR: Proton-transfer-reaction mass spectrometry (PTR-MS) was deployed for continuous real-time monitoring of volatile organic compounds (VOCs) at a site near the Houston Ship Channel during the Texas Air Quality Study 2000.
Abstract: [1] Proton-transfer-reaction mass spectrometry (PTR-MS) was deployed for continuous real-time monitoring of volatile organic compounds (VOCs) at a site near the Houston Ship Channel during the Texas Air Quality Study 2000. Overall, 28 ions dominated the PTR-MS mass spectra and were assigned as anthropogenic aromatics (e.g., benzene, toluene, xylenes) and hydrocarbons (propene, isoprene), oxygenated compounds (e.g., formaldehyde, acetaldehyde, acetone, methanol, C7 carbonyls), and three nitrogencontaining compounds (e.g., HCN, acetonitrile and acrylonitrile). Biogenic VOCs were minor components at this site. Propene was the most abundant lightweight hydrocarbon detected by this technique with concentrations up to 100+ nmol mol � 1 , and was highly correlated with its oxidation products, formaldehyde (up to � 40 nmol mol � 1 ) and acetaldehyde (up to � 80 nmol/mol), with typical ratios close to 1 in propene-dominated plumes. In the case of aromatic species the high time resolution of the obtained data set helped in identifying different anthropogenic sources (e.g., industrial from urban emissions) and testing current emission inventories. A comparison with results from complimentary techniques (gas chromatography, differential optical absorption spectroscopy) was used to assess the selectivity of this on-line technique in a complex urban and industrial VOC matrix and give an interpretation of mass scans obtained by ‘‘soft’’ chemical ionization using proton-transfer via H3O + . The method was especially valuable in monitoring rapidly changing VOC plumes which passed over the site, and when coupled with meteorological data it was possible to identify likely sources. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: PTR-MS, VOC, air quality, Houston, ozone
TL;DR: In this article, the first principle solvation-included electronic structure study of the hydrated electron in water is presented, where the authors compare a variety of candidate electronic structures of the electron and determine its absolute hydration free energy ΔGhyd298(e-).
Abstract: We report the first first-principles solvation-included electronic structure study to energetically compare a variety of candidate structures of the hydrated electron and to determine its absolute hydration free energy ΔGhyd298(e-). The calculated results show that both the thermal motion and bulk solvent effects can qualitatively change the relative thermodynamic stability of different structures of the hydrated electron on the basis of a cluster of a given size, and that the most stable structure in solution is not necessarily the most stable one in the gas phase. For a given number of explicitly included solvent water molecules, the most stable structure in solution reveals a unique feature of the chemical nature of the solvated electron in water, i.e., the electron forms two strong electron−hydrogen bonds of the e-···HO type with the hydrogen-bonded water cluster and two of the hydrogen bonds in the neutral water cluster are broken. On the basis of the most stable structures, the calculated electronic...
TL;DR: In this article, the results of an accurate density-functional study of the structure, energetics and electronic structure of Ptn clusters (with n = 13, 38, and 55) are presented.
Abstract: The results of an accurate density-functional study of the structure, energetics and electronic structure of Ptn clusters (with n = 13, 38, and 55) are presented. For Pt38, a truncated octahedral geometry is considered; for Pt13 and Pt55, icosahedral, truncated decahedral, and cuboctahedral geometries are considered. In each case, the structure of the neutral and positively and negatively charged clusters is fully optimized within the given symmetry group. For Pt13, allowing symmetry breaking starting from the symmetrical structures derives additional local minima. The computational procedure is thoroughly tested to keep numerical accuracy under control. From the electronic structure point of view, it is found that these systems start developing metallic characteristics, with ionization introducing small changes. From the structural point of view, for Pt13 the icosahedral configuration is not favored, whereas it becomes the ground state for Pt55, in agreement with the predictions of atom−atom potentials. ...
TL;DR: In this article, large-scale multireference configuration interaction, as well as coupled cluster, wave functions have been used in conjunction with a series of correlation consistent basis sets to calculate the near-equilibrium potential energy functions of the first two electronic states of HgO.
Abstract: One of the possible key products in the oxidation and transport of atmospheric mercury is mercury monoxide, HgO. In the present work, large-scale multireference configuration interaction, as well as coupled cluster, wave functions have been used in conjunction with a series of correlation consistent basis sets to calculate the near-equilibrium potential energy functions of the first two electronic states of HgO. In the absence of spin−orbit coupling, the lowest 1Σ+ and 3Π states are nearly isoenergetic with a binding energy with respect to ground-state atoms of only 2−3 kcal/mol at the estimated complete basis set limit. After spin−orbit coupling effects are accurately included, the resulting X0+ state has a D0 of just 4.0 kcal/mol, leading to a ΔHf(0 K) of 70.4 kcal/mol. These values are in stark contrast to the currently accepted experimental values. The implications of these results to atmospheric mercury chemistry are briefly discussed.
TL;DR: In this article, a uniform, comprehensive theoretical interpretation of spectroscopic data is presented for 51 radical ion species of polycyclic aromatic hydrocarbons (PAHs) with the aid of (Tamm−Dancoff) time-dependent density functional theory (TDDFT).
Abstract: A uniform, comprehensive theoretical interpretation of spectroscopic data is presented for 51 radical ion species of polycyclic aromatic hydrocarbons (PAHs) with the aid of (Tamm−Dancoff) time-dependent density functional theory (TDDFT). TDDFT is capable of predicting the transition energies to the low-lying excited states of PAH ions with quantitative accuracy (the standard deviation from experimental results being less than 0.3 eV) and their intensity patterns qualitatively correctly. The accuracy is hardly affected by the sizes of PAH ions (azulene through dinaphthocoronene), the types of transitions (Koopmans or satellite transitions), the types of orbitals involved (π* ← π, π* ← σ, or σ* ← π transitions), the types of ions (cations or anions), or other geometrical or electronic perturbations (nonplanarity, sp3 carbons, or heterocyclic or nonbenzenoid rings).
TL;DR: Modeling demonstrated that, for short reaction delays, dissociation of these peptides is solely determined by shattering, which results in much better sequence coverage for the singly protonated peptides than dissociation patterns obtained with any of the slow activation methods.
Abstract: Time- and collision energy-resolved surface-induced dissociation (SID) of des-Arg(1)- and des-Arg(9)-bradykinin on a fluorinated self-assembled monolayer (SAM) surface was studied by use of a novel Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Time-resolved fragmentation efficiency curves (TFECs) were modeled by an RRKM-based approach developed in our laboratory that utilizes a very flexible analytical expression for the internal energy deposition function capable of reproducing both single- and multiple-collision activation in the gas phase and excitation by collisions with a surface. Both experimental observations and modeling establish a very sharp transition in the dynamics of ion-surface interaction: the shattering transition. The experimental signature for this transition is the appearance of prompt (time-independent) fragmentation, which becomes dominant at high collision energies. Shattering opens a variety of dissociation pathways that are not accessible to slow collisional and thermal ion activation. This results in much better sequence coverage for the singly protonated peptides than dissociation patterns obtained with any of the slow activation methods. Modeling demonstrated that, for short reaction delays, dissociation of these peptides is solely determined by shattering. Internal energies required for shattering transition are approximately the same for des-Arg(1) and des-Arg(9)-bradykinin, resulting in the overlap of fragmentation efficiency curves obtained at short reaction delays. At longer delay times, parent ions depletion is mainly determined by a slow decay rate and fragmentation efficiency curves for des-Arg(1) and des-Arg(9)-bradykinin diverge. Dissociation thresholds of 1.17 and 1.09 eV and activation entropies of -22.2 and -23.3 cal/(mol K) were obtained for des-Arg(1) and des-Arg(9)-bradykinin from RRKM modeling of time-resolved data. Dissociation parameters for des-Arg(1)-bradykinin are in good agreement with parameters derived from thermal experiments. However, there is a significant discrepancy between the thermal data and dissociation parameters for des-Arg(9)-bradykinin obtained in this study. The difference is attributed to the differences in conformations that undergo thermal activation and activation by ion-surface collisions prior to dissociation.
TL;DR: To eliminate m/z discrimination in the external ion trap, further increase duty cycle, and improve MMA, the capability for data-dependent adjustment of ion accumulation times in the course of an LC separation is developed, referred to as automated gain control (AGC).
Abstract: When combined with capillary LC separations, electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) has demonstrated capabilities for advanced characterization of proteomes based upon analyses of proteolytic digests. Incorporation of external (to the ICR cell) multipole devices with FTICR for ion selection and ion accumulation has enhanced the dynamic range, sensitivity, and duty cycle of measurements. However, the highly variable ion production rate from an LC separation can result in “overfilling” of the external trap during the elution of major peaks and result in m/z discrimination and fragmentation of peptide ions. Excessive space charge trapped in the ICR cell also causes significant shifts in the detected ion cyclotron frequencies, reducing the achievable mass measurement accuracy (MMA) and making protein identification less effective. To eliminate m/z discrimination in the external ion trap, further increase duty cycle, and improve MMA, we have developed...
TL;DR: In this article, a comparison of the observed far-infrared (FIR) spectrum of Cl−-containing hydrotalcite, [Mg3Al(OH)8]Cl·3H2O, to a power spectrum calculated using molecular dynamics (MD) computer simulation, provides a greatly increased understanding of the structure and vibrational dynamics in the interlayers of layered double hydroxides.
Abstract: Comparison of the observed far-infrared (FIR) spectrum of Cl−-containing hydrotalcite, [Mg3Al(OH)8]Cl·3H2O, to a power spectrum calculated using molecular dynamics (MD) computer simulation, provides a greatly increased understanding of the structure and vibrational dynamics in the interlayers of layered double hydroxides. Good agreement between the observed FIR band positions and the simulated power spectrum illustrates the capability of this combination of experimental and computational techniques to effectively probe the structure and dynamics of water in nano-pores and other confined spaces. The simulation model assumes an ordered Mg3Al arrangement in the octahedral sheet and no constraints on the movement of any atoms or on the geometry and symmetry of the simulation supercell. Calculated anisotropic components of the individual atomic power spectra in combination with computed animations of the vibrational modes from normal mode analysis allow for reliable interpretations of the observed spectral bands. For the vibrations related to octahedral cation motions, bands near 145, 180, and 250 cm−1 are due dominantly to Mg vibration in the c direction (perpendicular to the hydroxide layers), Al vibration in the c direction, and Mg and Al vibrations in the a-b plane (parallel to the hydroxide layers), respectively. The low frequency vibrational motions of the interlayer are controlled by a network of hydrogen bonds formed between interlayer water molecules, Cl− ions, and the OH groups of the main hydroxide layers. The bands near 40–70 cm−1 are related to the translational motions of interlayer Cl− and H2O in the a-b plane, and the bands near 120 cm−1 and 210 cm−1 are largely due to translational motions of the interlayer species in the c direction. The three librational modes of interlayer water molecules near 390, 450, and 540 cm−1 correspond to twisting, rocking, and wagging hindered rotations, respectively. The spectral components of the interlayer Cl− motions are remarkably similar to those of bulk aqueous chloride solutions, reflecting the structural and dynamic similarity of the nearest-neighbor Cl− environments in the interlayer and in solution.