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 spectra of CH3-MH through methane activation by laser-ablated Sn, Pb, Sb, and Bi atoms.

Abstract: Methane activation has been carried out by laser-ablated Sn, Pb, Sb, and Bi atoms. All four metals generate the insertion complex (CH3–MH), but subsequent H-migration from C to M to form CH2–MH2 and CH–MH3 complexes is not observed. Our previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals. The C–H bond insertion evidently occurs during reaction on sample condensation, and the product dissociates on broad-band photolysis afterward. The insertion complex contains a near right angle C–M–H moiety because of high p contribution from the metal center to the C–M and M–H bonds unlike many transition-metal analogues. The computed methylidene structures for these main group metals are not agostic possibly because of the absence of valence d-orbitals.

Infrared spectra of isotopic (HCl) 3 clusters in solid neon

Abstract: The codeposition of Ne/HCl mixtures at 5 K leads to the formation of a large yield of (HCl)3 which exhibits one sharp fundamental at 2801.5 cm−1 with chlorine isotopic splittings at 2800.2 and 2799.4 cm−1. Deuterium substitution gives rise to the three stretching fundamentals for (HCl)2(DCl) and (HCl)(DCl)2 with resolved chlorine isotopic splittings that identify these clusters. The neon matrix observations confirm the argon matrix assignments and characterization of (HCl)3 as a C3h cyclic species by the Perchard group and predict a strong gas phase band at 2816±3 cm−1.

Matrix Infrared Spectra and Density Functional Calculations for GaNO, InNO, and TlNO

Abstract: Laser-ablated Ga, In, and Tl atoms react with NO during condensation in excess argon at 10 K to give one major product, which absorbs at 1578.5 cm-1 for Ga, 1524.9 cm-1 for In, and 1454.6 cm-1 for Tl. Infrared spectra of 14N16O, 15N16O, 15N18O, and mixed isotopic samples show that this product is the metal nitrosyl MNO. Density functional calculations provide good agreement for 3Σ- GaNO and InNO, but higher level MP2 calculations are required to explain the bent structure and decreased N−O frequency for 3A‘ ‘ TlNO. Model DFT calculations are also reported for Li[NO] and Li[NO]Li.

Matrix reactions of silane and germane with fluorine: infrared spectra of several hydrogen fluoride product complexes

Abstract: Silane and germane were condensed with F 2 at high dilution in argon on a 13±1K substrate. Weak product complexes produced on condensation and increased by ultraviolet photolysis are assigned to SiH 3 F--HF, SiH 2 --HF or SiH 2 --(HF) 2 , and HSiF--HF. Annealing produced new bands due to F atom reactions that are attributed to SiH 3 --HF. The GeH 3 F molecule was observed in the similar GeH 3 F--HF complex.

Matrix infrared spectroscopic and theoretical investigations of uranium atom and methanol reaction products.

Abstract: Reactions of laser-ablated uranium atoms and methanol are investigated in solid argon using matrix isolation and infrared spectroscopy. Four new product molecules are identified with the help of isotopically substituted methanol as well as density functional frequency calculations. Uranium atoms react spontaneously with methanol on annealing to form the U(II) insertion product CH3OUH, which has a quintet ground state with strong C—O and U—H stretching vibrations. Further sample annealing allows the reaction of CH3OUH and another methanol molecule to eliminate H2 and give the U(OCH3)2 product. Near-UV–vis irradiation isomerizes the CH3OUH molecule to the 32 kcal/mol lower energy U(IV) CH3U(O)H isomer and the U(OCH3)2 molecule to the 28 kcal/mol lower energy CH3OU(O)CH3 isomer. Both U(IV) products have triplet ground states, U═O double bonds, and pyramidal skeletal structures.

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