Thermochemistry of SiO(OH) Vapor Species from Quantum Chemical Calculations.

The thermochemistry of the Si-O-H system has been extensively studied both experimentally and theoretically due to its importance in chemical processes, degradation of silica-protected materials in combustion, and geological processes. In this paper, we review past studies and use quantum mechanical methods to generate a new data set. Molecular geometries were generated with DFT using the B3LYP functional.

Modeling Singlet Oxygen-Induced Degradation Pathways Including Environmental Effects of 1,2-Dimethoxyethane in Li-O Batteries through Density Functional Theory.

We employ density functional theory (DFT) to examine reaction mechanisms involving singlet oxygen Δ (O) and 1,2-dimethoxyethane (DME) to probe potential parasitic reactions occurring in Li-O batteries. First, we investigate the attack of O on the ethylene group (-CH-CH-) to form HO and a C-C double bond in a single step. Second, we look at hydroperoxide formation that occurs via a two-step mechanism.

Quantum chemical and experimental thermodynamic studies of HfO(g).

Hafnium dioxide vaporizes primarily to HfO(g) in a reducing environment. The thermochemistry of HfO(g) is calculated from quantum methods and measured via Knudsen effusion mass spectrometry. For the computations, all-electron and relativistic effective core potential calculations are used.

Computational Chemistry Derivation of Cr, Mn, and La Hydroxide and Oxyhydroxide Thermodynamics.

Thermodynamic quantities are calculated for gaseous hydroxides and oxyhydroxides of Cr, Mn, and La. These would form due to water-vapor-containing environments reacting with Cr-forming alloys or oxide components of potential fuel cell interconnects or anode materials. Structures and vibrational modes for the expected hydroxides and oxyhydroxides are calculated with the B3LYP hybrid functional.

Reaction of Singlet Oxygen with the Ethylene Group: Implications for Electrolyte Stability in Li-Ion and Li-O Batteries.

Recent experimental and computational evidence indicates that singlet oxygen (O) attacks the ethylene group (-CH-CH-) in ethylene carbonate (EC) leading to degradation in Li-ion batteries employing EC as the electrolyte solvent [ , , 8828-8839]. Here, we employ computational quantum chemistry to explore this mechanism in detail for a large set of organic molecules. Benchmark calculations comparing density functional theory to the complete active space second-order perturbation theory and internally contracted multireference configuration interaction indicate that the M11 functional adequately captures trends in the transition-state energies for this mechanism.

Thermochemistry of Gaseous Ytterbium and Gadolinium Hydroxides and Oxyhydroxides.

GdO and YbO are the proposed constituents of advanced coating systems in combustion environments. In such environments, they are exposed to high-temperature water vapor, which would lead to gaseous hydroxide formation. Thermodynamic parameters are reported for YbO(OH) and GdO(OH) species.

Proton Abstraction from DME ···X by OH, O, and XO, for X = Li, Na, and K: Implications for Li-O Batteries.

The abstraction of a proton by OH, O, and XO from DME ···X, where X is Li, Na, or K, is studied using density functional theory. Both the gas phase and the solution phase are studied. In general, when explicit solvent molecules are added, the difference between the gas-phase and solution results becomes rather small.

POLYCYCLIC AROMATIC HYDROCARBONS WITH STRAIGHT EDGES AND THE 7.6/6.2 AND 8.6/6.2 INTENSITY RATIOS IN REFLECTION NEBULAE.

We have investigated the mid-infrared spectral characteristics of a series of polycyclic aromatic hydrocarbons (PAHs) with straight edges and containing an even or odd number of carbons using density functional theory (DFT). For several even and odd-carbon PAHs, the 8.6/6.

Li-ligand binding energies and the effect of ligand fluorination on the binding energies.

The Li-ligand binding energies are computed for seven ligands and their perfluoro analogs using Density Functional Theory. The bonding is mostly electrostatic in origin. Thus the size of the binding energy tends to correlate with the ligand dipole moment, however, the charge-induced dipole contribution can be sufficiently large to affect the dipolebinding energy correlation.

Computational and Experimental Study of Thermodynamics of the Reaction of Titania and Water at High Temperatures.

Gaseous titanium hydroxide and oxyhydroxide species were studied with quantum chemical methods. The results are used in conjunction with an experimental transpiration study of titanium dioxide (TiO) in water vapor-containing environments at elevated temperatures to provide a thermodynamic description of the Ti(OH)(g) and TiO(OH)(g) species. The geometry and harmonic vibrational frequencies of these species were computed using the coupled-cluster singles and doubles method with a perturbative correction for connected triple substitutions [CCSD(T)].

The low-lying electronic states of MgO.

The low-lying singlet and triplet states of MgO have been studied using a SA-CASCF/IC-MRCI approach using the aug-cc-pV5Z basis set. The spectroscopic constants ( , , and ) are in good agreement with the available experimental data. The computed lifetime for the state is in excellent agreement with two of the three experimental results.

Infrared spectroscopy of matrix-isolated neutral polycyclic aromatic nitrogen heterocycles: The acridine series.

The matrix-isolated, mid-infrared spectra of seven acridine-based polycyclic aromatic nitrogen heterocycles (PANHs) have been measured and compared to their non-nitrogen containing parent molecule. The acridine species investigated include acridine, benz[a]acridine, benz[c]acridine, dibenz[a,j]acridine, dibenz[c,h]acridine, dibenz[a,h]acridine and dibenz[a,c]acridine. The previously reported results for 1 and 2-azabenz[a]anthracenes are included for comparison.

Phenolic Polymer Solvation in Water and Ethylene Glycol, II: Ab Initio Computations.

Ab initio techniques are used to study the interaction of ethylene glycol and water with a phenolic polymer. The water bonds more strongly with the phenolic OH than with the ring. The phenolic OH groups can form hydrogen bonds between themselves.

Phenolic Polymer Solvation in Water and Ethylene Glycol, I: Molecular Dynamics Simulations.

Interactions between pre-cured phenolic polymer chains and a solvent have a significant impact on the structure and properties of the final postcured phenolic resin. Developing an understanding of the nature of these interactions is important and will aid in the selection of the proper solvent that will lead to the desired final product. Here, we investigate the role of the phenolic chain structure and the solvent type on the overall solvation performance of the system through molecular dynamics simulations.

Ab Initio Simulations and Electronic Structure of Lithium-Doped Ionic Liquids: Structure, Transport, and Electrochemical Stability.

Density functional theory (DFT), density functional theory molecular dynamics (DFT-MD), and classical molecular dynamics using polarizable force fields (PFF-MD) are employed to evaluate the influence of Li(+) on the structure, transport, and electrochemical stability of three potential ionic liquid electrolytes: N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([pyr14][TFSI]), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ([pyr13][FSI]), and 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF4]). We characterize the Li(+) solvation shell through DFT computations of [Li(Anion)n]((n-1)-) clusters, DFT-MD simulations of isolated Li(+) in small ionic liquid systems, and PFF-MD simulations with high Li-doping levels in large ionic liquid systems. At low levels of Li-salt doping, highly stable solvation shells having two to three anions are seen in both [pyr14][TFSI] and [pyr13][FSI], whereas solvation shells with four anions dominate in [EMIM][BF4].

Structure and energetics of Li(+)-(BF4(-))n, Li(+)-(FSI(-))n, and Li(+)-(TFSI(-))n: ab initio and polarizable force field approaches.

The Li(+)-BF4(-) and BF4(-)-BF4(-) interactions are studied using second order perturbation theory (MP2) and coupled cluster singles and doubles approach, including the effect of connected triples, CCSD(T). The MP2 and CCSD(T) results are in excellent agreement. Using only the MP2 approach, the interactions of Li(+) with bis(trifluoromethane)sulfonimide anion (TFSI) and Li(+) with bis(fluorosulfonyl)imide anion (FSI) are studied.

Computational and experimental investigation of Li-doped ionic liquid electrolytes: [pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4].

We employ molecular dynamics (MD) simulation and experiment to investigate the structure, thermodynamics, and transport of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsufonyl)imide ([pyr14][TFSI]), N-methyl-N-propylpyrrolidinium bis(fluorosufonyl)imide ([pyr13][FSI]), and 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF4]), as a function of Li-salt mole fraction (0.05 ≤ xLi(+) ≤ 0.33) and temperature (298 K ≤ T ≤ 393 K).

Infrared vibrational and electronic transitions in the dibenzopolyacene family.

We report experimental spectra in the mid-infrared (IR) and near-IR for a series of dibenzoacenes isolated in Ar matrices. The experiments are supported by Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations with both vibrational and electronic transitions studied. For the neutrals, we find good agreement between the experimental and B3LYP and BP86 results for all species studied.

Comparison of ReaxFF, DFTB, and DFT for phenolic pyrolysis. 1. Molecular dynamics simulations.

A systematic comparison of atomistic modeling methods including density functional theory (DFT), the self-consistent charge density-functional tight-binding (SCC-DFTB), and ReaxFF is presented for simulating the initial stages of phenolic polymer pyrolysis. A phenolic polymer system is simulated for several hundred picoseconds within a temperature range of 2500 to 3500 K. The time evolution of major pyrolysis products including small-molecule species and char is examined.

Comparison of ReaxFF, DFTB, and DFT for phenolic pyrolysis. 2. Elementary reaction paths.

Reaction paths for the loss of CO, H2, and H2O from atomistic models of phenolic resin are determined using the hybrid B3LYP approach. B3LYP energetics are confirmed using CCSD(T). The energetics along the B3LYP paths are also evaluated using the PW91 generalized gradient approximation (GGA), the more approximate self-consistent charge density functional tight binding (SCC-DFTB), and the reactive force field (ReaxFF).

Reactions of group 3 metals with OF2: infrared spectroscopic and theoretical investigations of the group 3 oxydifluoride OMF2 and oxyfluoride OMF molecules.

The oxidifluoride molecules, OYF(2) and OLaF(2), are produced via the reactions of laser ablated metal atoms with OF(2) in solid argon. The product structures are characterized using matrix isolation infrared spectroscopy as well as theoretical calculations. Similar to the very recently characterized OScF(2) molecule, OYF(2) is predicted to have a (2)B(2) ground state with C(2v) symmetry while the heavier OLaF(2) has a (2)A″ ground state with near C(2v) symmetry.

Formation of metal oxyfluorides from specific metal reactions with oxygen difluoride: infrared spectroscopic and theoretical investigations of the OScF2 radical and OScF with terminal single and triple Sc-O bonds.

The scandium oxydifluoride free radical, OScF(2), is produced by the spontaneous, specific reaction of laser ablated Sc atoms with OF(2) in solid argon and characterized by using matrix infrared spectroscopy and theoretical calculations. The OScF(2) molecule is predicted to have C(2v) symmetry and a (2)B(2) ground state with an unpaired electron located primarily on the terminal oxygen atom, which makes it a scandium difluoride molecule coordinated by a neutral oxygen atom radical in forming the Sc-O single bond. The closed shell singlet OScF molecule with an obtuse bent geometry has a much shorter Sc-O bond of 1.

Infrared spectroscopic and theoretical studies of the OTiF2, OZrF2 and OHfF2 molecules with terminal oxo ligands.

The isolated group 4 metal oxydifluoride molecules OMF(2) (M = Ti, Zr, Hf) with terminal oxo groups are produced specifically on the spontaneous reactions of metal atoms with OF(2) through annealing in solid argon. The product structures and vibrational spectra are characterized using matrix isolation infrared spectroscopy as well as B3LYP density functional and CCSD(T) frequency calculations. OTiF(2) is predicted to have a planar structure while both OZrF(2) and OHfF(2) possess pyramidal structures, all with singlet ground states.

Optical properties of (GaAs)n clusters (n = 2-16).

The electronic and geometrical structures of the lowest triplet states of (GaAs) n clusters ( n = 2-16) are studied using density functional theory with generalized gradient approximation (DFT-GGA). It is found that the triplet-state geometries are different from the corresponding singlet-state geometries; for n = 2-8, 10, and 11, the triplets and singlets have different topologies, while the (GaAs) 9, (GaAs) 12, (GaAs) 15, and (GaAs) 16 triplets possess a reduced symmetry, due to Jahn-Teller distortions. Except for GaAs, the singlet states are the ground states.

Electronic and geometrical structure of Mn13 anions, cations, and neutrals.

We have computed the electronic and geometrical structures of thirteen atom manganese clusters in all three charge states, Mn(13) (-), Mn(13) (+), and Mn(13) by using density functional theory with the generalized gradient approximation. Our results for Mn(13) (-) are compared with our anion photoelectron spectrum of Mn(13) (-), published in this paper. Our results for Mn(13) (+) are compared with the previously published photoionization results of Knickelbein [J.