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.

Infrared Spectroscopic Studies of Mono-, Di-, and Trihydrido C-H Insertion Complexes Formed in Reaction of Ethylene with Laser-Ablated Hafnium Atoms and Isolated in a Solid Argon Matrix

Abstract: The C-H insertion reaction of laser-ablated Hf atoms with ethylene in excess argon has been carried out during codeposition at 7 K, and the reaction products have been investigated by means of infrared spectroscopy. Parallel to the case of Zr, mono-, di-, and trihydrido C-H insertion complexes are identified. Among them, the mono- and dihydrido C-H insertion complexes are reaction intermediates of hydrogen elimination from ethylene by second-row transition-metal atoms presumed in previous reaction dynamics studies. The higher Hf-H stretching frequencies and shorter Hf-H and C-Hf bond lengths of the hafnium C-H insertion products than those of the zirconium products are attributed to the shortened bonds of the heavier metal atom by relativistic effects.

Reactions of Selenium in a Quartz Discharge Tube. Infrared Spectra and Density Functional Theory Calculations of New Selenium−Nitrogen and Selenium−Silicon Species in Solid Argon

Abstract: New selenium−nitrogen species were produced by condensing the effluent from an argon/nitrogen/selenium microwave discharge onto a 12 K substrate. Nitrogen-15 and selenium-76 and −80 isotopic substitutions, photolysis, and annealing provided basis for identification of the new product absorptions in the infrared spectrum. A weak band at 951 cm-1 is assigned to SeN and the very strong 1019 cm-1 band to ν3 of NSe2 radical with a 146 ± 5° valence angle. A new 1570 cm-1 band in this system is due to the SeNO radical, and a 1771 cm-1 absorption, also made from Se2 and NO, is due to the (SeSe)(NO) complex. Higher-order SexNy (x > 1) species give rise to bands at 904, 736, 616, and 529 cm-1. The argon/selenium discharge in quartz has also produced the SiSe, SiSe2, and SeSiO species. Structure and frequency calculations using density functional theory support the matrix infrared identification of these new selenium molecular species. The most stable (NSe)2 structure is calculated to be the cis form analogous to (N...

Thorium and Uranium Hydride Phosphorus and Arsenic Bearing Molecules with Single and Double Actinide-Pnictogen and Bridged Agostic Hydrogen Bonds.

Abstract: Thorium atoms from laser ablation react with phosphine during condensation in excess argon to produce two new infrared absorptions at 1467.2 and 1436.6 cm–1 near weak bands for ThH and ThH2, which increase on annealing to 25 and 30 K, indicating spontaneous reactions. Analogous experiments with uranium produced two similar bands at 1473.4 and 1456.7 cm–1 above UH at 1423.8 cm–1 and another absorption at 1388.2 cm–1. Electronic structure calculations at the coupled cluster CCSD(T) for Th and density functional theory calculations for U as well as their proximity to other actinide hydride absorptions support assignments of these bands to the simplest molecules HP═ThH2, HP═UH2, and PH2–UH. Arsine gave the analogous products HAs═ThH2, HAs═UH2, and AsH2–UH. The HE═AnH2 molecules (E = P, As; An = Th, U) have strong agostic An–H(E) interactions with H–E–An angles in the range of 60–64°. The calculated agostic bond distances are 9% to 12% longer than terminal single An–H bonds, which suggests that these strong ag...

Quantum-chemical calculations and IR spectra of the (F2)MF2 molecules (M = B, Al, Ga, In, Tl) in solid matrices: a new class of very high electron affinity neutral molecules.

Abstract: Electron-deficient group 13 metals react with F2 to give the compounds MF2 (M = B, Al, Ga, In, Tl), which combine with F2 to form a new class of very high electron affinity neutral molecules, (F2)MF2, in solid argon and neon. These (F2)MF2 fluorine metal difluoride molecules were identified through matrix IR spectra containing new antisymmetric and symmetric M−F stretching modes. The assignments were confirmed through close comparisons with frequency calculations using DFT methods, which were calibrated against the MF3 molecules observed in all of the spectra. Electron affinities calculated at the CCSD(T) level fall between 7.0 and 7.8 eV, which are in the range of the highest known electron affinities.

A Chemist's Guide to Density Functional Theory

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.

The density functional formalism, its applications and prospects

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.

The Halogen Bond

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.

Generation and Detection of Reactive Oxygen Species in Photocatalysis

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...

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

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