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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: In this paper, the first thorium carbonyl complex, ThCO, which rearranges to CThO, was described, which is a relatively new area of research, in part because of the experimental challenges faced in handling and characterizing actinide complexes.
Abstract: Transition metal carbonyl complexes, M(CO){sub n}, are cornerstones of modern coordination chemistry and organometallic chemistry. Carbon monoxide activation and reduction by transition metal atoms are important in a great many industrial processes. By contrast, the coordination chemistry of CO with the actinide elements is a relatively new area of research, in part because of the experimental challenges faced in handling and characterizing actinide complexes. The authors report a study of reactions of laser-ablated thorium atoms with carbon monoxide in excess neon. These experiments form the first thorium carbonyl complex, ThCO, which rearranges to CThO. Although this chemistry seems to parallel to that of CO with uranium atoms, it is distinctly different because of the intrinsic differences between Th and U.

51 citations

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TL;DR: In this article, the vibrational frequencies of the OYO and OLaO molecules were analyzed and their symmetric stretching modes were found to be unusually intense and weakly bound.
Abstract: Laser-ablated Y and La condensed with O2 in excess argon formed small metal oxides, cations, and anions, which were identified from isotopic substitution and density functional frequency calculations. In accord with gas phase thermochemistry, the OYO and OLaO molecules are more weakly bound than YO and LaO, on the basis of vibrational frequencies, and their symmetric stretching modes are unusually intense. The bent OYO- and OLaO- anions, the cyclic Y(O2)+ and La(O2)+, and linear OLaO+ cation isomers are characterized. The (O2)MO and MO3 isomers are also observed.

50 citations

Journal ArticleDOI
TL;DR: In this article, laser ablation atoms were reacted with dioxygen diluted in argon during condensation at 10 K. Density functional theory (B3LYP) calculations were performed on product molecules, which were identified on the basis of isotopic frequency shifts and correlation with density functional calculations.
Abstract: Platinum and palladium atoms produced by laser ablation were reacted with dioxygen diluted in argon during condensation at 10 K. Reaction products, including the M(O2) and (O2)M(O2) complexes prepared with thermal metal atoms, and the platinum oxides PtO, OPtO, PtO3, OOPtO, and (O2)PtO, were analyzed by matrix infrared spectroscopy. Absorptions due to PdO and OPdO were not identified. Density functional theory (B3LYP) calculations were performed on product molecules, which were identified on the basis of isotopic frequency shifts and correlation with density functional calculations. The most interesting new molecule produced here, linear OPtO, can also be produced by photolysis of the cyclic Pt(O2) complex.

50 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a series of radicals CCl3, CCl2Br and CClBr2 to verify the molecular identity of dibromocarbene and the tribromomethyl radical.
Abstract: Simultaneous condensation at 15°K of beams of lithium atoms and carbon tetrabromide diluted in argon produces infrared absorptions which are identified as lithium bromide and the tribromomethyl radical. Comparisons within the series of radicals CCl3, CCl2Br, CClBr2, and CBr3 verify the molecular identity. Assignments to the carbon–bromine stretching vibrations are ν1 = 582 cm−1 and v3 = 773 cm−1, whereas the bending modes v2 and v4 were not observed. The stretching force constants Fr = 3.55 mdyn/A and Frr = 0.70 mdyn/A are compared with those of other bromocarbons and BBr3. The high carbon–bromine stretching‐force constant can be rationalized by the fact that the tribromomethyl radical is resonance stabilized. Secondary reaction of lithium atoms with the tribromomethyl radical yields a sufficient concentration of dibromocarbene for infrared spectral study. Variation of the perbromochloromethane precursors and loss of CBr2 absorptions with attendant growth of the most intense C2Br4 absorption on sample warming furnish convincing evidence that dibromocarbene is isolated in the argon matrix. Assignments to the carbon–bromine stretching vibrations are v1 = 595.0 cm−1 and v3 = 640.5 cm−1, and the bending mode was not detected. The stretching‐force constants Fr = 2.38 mdyn/A and Frr = 0.18 mydn/A indicate that C–Br single bonds are present in dibromocarbene, making it unlikely that the electron deficiency of the carbon atom is relieved by pi bonding with bromine.

50 citations

Journal ArticleDOI
TL;DR: In this paper, laser-ablated coinage metal atom reactions with H2 in excess argon, neon, and pure hydrogen are investigated through matrix infrared spectroscopy, and the reaction products are identified by isotopic substitution (D2, HD, and H2 + D2) and verified by DFT calculations of vibrational fundamentals.
Abstract: Laser-ablated coinage metal atom reactions with H2 in excess argon, neon, and pure hydrogen are investigated through matrix infrared spectroscopy. The reaction products are identified by isotopic substitution (D2, HD, and H2 + D2) and verified by DFT calculations of vibrational fundamentals. The MH and (H2)MH molecules are observed for all group 11 metals, and the trihydride complex (H2)AuH3 is stabilized in pure hydrogen. The (H2)CuH and (H2)AgH complexes exhibit weak H−H stretching fundamentals at 3805.9 and 3566.6 cm-1 and strong Cu−H and Ag−H stretching modes at 1861.4 and 1742.6 cm-1, respectively. In addition, (H2)CuH reacts further with Cu to give (H2)CuHCu, and Au (2P) inserts to form AuH2 in pure hydrogen. The cluster hydrides M2H and M2H- anions are also formed in these experiments.

50 citations


Cited by
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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