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Lester Andrews

Bio: Lester Andrews is an academic researcher from University of Virginia. The author has contributed to research in topics: Infrared spectroscopy & Molecule. The author has an hindex of 68, co-authored 888 publications receiving 24613 citations. Previous affiliations of Lester Andrews include Ames Research Center & Environmental Molecular Sciences Laboratory.


Papers
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Journal ArticleDOI
TL;DR: Several new platinum nitride species are produced by the reaction of laser-ablated platinum with pure nitrogen, and their frequencies calculated by density functional theory in addition to the complexes observed in earlier thermal atom studies as mentioned in this paper.
Abstract: Several new platinum nitride species are produced by the reaction of laser-ablated platinum with pure nitrogen, and their frequencies calculated by density functional theory in addition to the complexes observed in earlier thermal atom studies. Platinum forms PtN and a number of molecules derived from PtN including NNPtN, PtPtN, Pt2N, and PtNNPt, and PtNNN from reaction with N3 radical in pure nitrogen. The PtNN complex is characterized by the Pt−N stretching mode at 499.6 cm-1 and its combination band at 2669.6 cm-1 with the strong N−N fundamental at 2168.5 cm-1 in solid argon. Absorptions are observed for PtxNN, PtNN-, Pt(NN)2-, and Pt(NN)2 in solid argon and neon.

25 citations

Journal ArticleDOI
TL;DR: In this article, the major products are best characterized as 1/1 [pi] complexes where the metal shares electron density from one acetylene [pi]- orbital, and higher reagent concentrations give evidence for 1/2 and 2/1 metal-acetylene complexes.
Abstract: Aluminum, gallium, and indium atoms have been codeposited from thermal sources with C[sub 2]H[sub 2] at high dilution in argon on a 12[plus minus]1 K CsI window. The major products are best characterized as 1/1 [pi] complexes where the metal shares electron density from one acetylene [pi] orbital. Higher reagent concentrations give evidence for 1/2 and 2/1 metal-acetylene complexes. In the case of aluminum, photolysis induces insertion to form HAlC[sub 2]H and AlC[sub 2]H.

25 citations

Journal ArticleDOI
TL;DR: In this article, the zirconium methylidene isocyanide, methyl isomethane, and η2-nitrile-π-complexes are observed in the matrix IR spectra from reactions of laser-ablated Zr atoms and acetonitrile isotopomers.
Abstract: The zirconium methylidene isocyanide, methyl isocyanide, and η2-nitrile-π-complexes are observed in the matrix IR spectra from reactions of laser-ablated Zr atoms and acetonitrile isotopomers. The methylidene CH2═Zr(H)NC has a C1 agostic structure in line with simple early transition-metal methylidenes recently produced from reactions with small alkanes and methyl halides, and the extent of agostic distortion is also comparable. Formation of the isocyanide complexes from acetonitrile is interesting but not surprising according to previous studies of metal reactions with nitrile-containing compounds, and their stabilities over the cyanide species are reproduced by DFT calculations. Observation of the relatively rare nitrile π-complex and its photodissociation suggests that the reaction proceeds in the order of Zr←NCCH3, η2-Zr(NC)—CH3, CH3—ZrNC, and CH2═Zr(H)NC. The intermediate transition-state structures are also examined.

25 citations

Journal ArticleDOI
TL;DR: In this article, Hartree-Fock (SCF) calculations were used to construct 1:1 complexes with methane, silane, and germane and showed that the IC inactive symmetric C-H stretch in CH4 was observed in the CH4−−FH complex as a weak band at 2914 cm−1.
Abstract: HF complexes with methane, silane, and germane were prepared in noble gas matrices and studied using infrared spectroscopy and Hartree–Fock (SCF) calculations. The spectra indicate that two types of 1:1 complexes were formed, a normal one in which the hydrogen of HF is interacting with one hydrogen of silane or germane, and a reverse complex in which the fluorine of HF is interacting with one hydrogen atom of methane. The IR inactive symmetric C–H stretch in CH4 was observed in the CH4‐‐FH complex as a weak band at 2914 cm−1. In the silane‐‐HF and germane‐‐HF complexes, the Si–H and Ge–H stretches were perturbed approximately 50 cm−1 to higher energy relative to the antisymmetric stretch ν3 in each parent molecule, but the ν1 modes were masked by the strong ν3 parent bands. Higher order 1:2 (AH4:HF) complexes were also observed and support the normal or reverse‐type geometry of the 1:1 complexes.

25 citations

Journal ArticleDOI
TL;DR: In this article, the reaction of laser-ablated Ru atoms with halomethanes and methane has been investigated, and the diagnostic C−H and C−X stretching absorptions of the carbyne complexes are observed on the blue side of the corresponding precursor bands.
Abstract: Reactions of laser-ablated Ru atoms with halomethanes and methane have been investigated. Small carbyne and carbene complexes or insertion products are produced in the reactions of halomethanes via C–X insertion and halogen migration, whereas only the insertion complex is formed in the reactions of methane. The results are consistent with computed product stabilities. The diagnostic C–H and C–X stretching absorptions of the carbyne complexes are observed on the blue side of the corresponding precursor bands. The high C–H and C–X stretching frequencies are explained with the higher s character in hybridization and combination with the C≡Ru stretching motion, respectively. The structures of the carbyne complexes are highly distorted and show a large variation with the ligands, and the extra electron pair on the Ru atom evidently plays an important role in the carbyne. In contrast to early transition-metal analogs, the Ru carbene complexes show no agostic distortion.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

25 citations


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Book
01 Sep 2001
TL;DR: A Chemist's Guide to Density Functional Theory should be an invaluable source of insight and knowledge for many chemists using DFT approaches to solve chemical problems.
Abstract: "Chemists familiar with conventional quantum mechanics will applaud and benefit greatly from this particularly instructive, thorough and clearly written exposition of density functional theory: its basis, concepts, terms, implementation, and performance in diverse applications. Users of DFT for structure, energy, and molecular property computations, as well as reaction mechanism studies, are guided to the optimum choices of the most effective methods. Well done!" Paul von RaguE Schleyer "A conspicuous hole in the computational chemist's library is nicely filled by this book, which provides a wide-ranging and pragmatic view of the subject.[...It] should justifiably become the favorite text on the subject for practioneers who aim to use DFT to solve chemical problems." J. F. Stanton, J. Am. Chem. Soc. "The authors' aim is to guide the chemist through basic theoretical and related technical aspects of DFT at an easy-to-understand theoretical level. They succeed admirably." P. C. H. Mitchell, Appl. Organomet. Chem. "The authors have done an excellent service to the chemical community. [...] A Chemist's Guide to Density Functional Theory is exactly what the title suggests. It should be an invaluable source of insight and knowledge for many chemists using DFT approaches to solve chemical problems." M. Kaupp, Angew. Chem.

3,550 citations

Journal ArticleDOI
TL;DR: In this paper, the authors survey the local density functional formalism and some of its applications and discuss the reasons for the successes and failures of the local-density approximation and some modifications.
Abstract: A scheme that reduces the calculations of ground-state properties of systems of interacting particles exactly to the solution of single-particle Hartree-type equations has obvious advantages. It is not surprising, then, that the density functional formalism, which provides a way of doing this, has received much attention in the past two decades. The quality of the energy surfaces calculated using a simple local-density approximation for exchange and correlation exceeds by far the original expectations. In this work, the authors survey the formalism and some of its applications (in particular to atoms and small molecules) and discuss the reasons for the successes and failures of the local-density approximation and some of its modifications.

3,285 citations

Journal ArticleDOI
TL;DR: The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.
Abstract: The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

2,582 citations

Journal ArticleDOI
TL;DR: The detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS) in photocatalysis were surveyed comprehensively and the major photocatalyst used in heterogeneous photocatalytic systems was found to be TiO2.
Abstract: The detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS), i.e., superoxide anion radical (•O2–), hydrogen peroxide (H2O2), singlet oxygen (1O2), and hydroxyl radical (•OH) in photocatalysis, were surveyed comprehensively. Consequently, the major photocatalyst used in heterogeneous photocatalytic systems was found to be TiO2. However, besides TiO2 some representative photocatalysts were also involved in the discussion. Among the various issues we focused on the detection methods and generation reactions of ROS in the aqueous suspensions of photocatalysts. On the careful account of the experimental results presented so far, we proposed the following apprehension: adsorbed •OH could be regarded as trapped holes, which are involved in a rapid adsorption–desorption equilibrium at the TiO2–solution interface. Because the equilibrium shifts to the adsorption side, trapped holes must be actually the dominant oxidation species whereas •OH in solution would exert the reactivity...

2,249 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations