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.

C-H activation of ethane by group 4 metal atoms: observation and characterization of the MH-CH2CH3, MH2-(CH2)2, and MH3-CH=CH2 complexes.

Abstract: Group 4 metal atoms excited in the laser ablation process activate ethane to form the C-H insertion product, the metallacyclopropane dihydride, and vinyl metal trihydride complexes as major products. These three new metal hydrides are characterized by their strong M-H stretching absorptions and other weaker modes as predicted by density functional theory vibrational frequency calculations.

Photochemistry of hydrogen sulfide-fluorine complexes in solid argon: infrared spectra of (HSF)(HF) complexes

Abstract: Codeposition of H 2 S and F 2 in excess argon on a cold window at 12±1 K gave sulfur fluorides and evidence for Lewis acid-base precursor complexes. Photolysis of these complexes with 590-1000-nm light formed several new products. Ab initio SCF calculations with the standard double-ζ plus polarization function (DZP) basis set were performed to support the identification of new product species. The HSF--HF and HFS--HF complexes exhibited H-F stretching modes at 3850 and 3724 cm -1 and S-F stretching modes at 759 and 816 cm -1 , respectively

Infrared Spectra of H2 Molecules Near H Atoms Trapped in Solid H2

Abstract: Laser-ablation irradiation of normal hydrogen during condensation at 3.8 K produces new IR absorptions in p-H2 and o-H2 cage molecules at 4151.8 and 4143.4 cm-1 that are redshifted 1.0 and 3.3 cm-1, respectively, from induced IR absorptions for each nuclear spin isomer in solid n-H2. Assignment to perturbed p-H2 and o-H2 molecules, respectively, are confirmed by experiments with p-H2-enriched samples. Deuterium experiments give rise to analogous bands for o-D2 and p-D2 at 2985.2 and 2982.4 cm-1, respectively, that are redshifted 1.6 and 2.2 cm-1 from the absorptions induced for each nuclear spin isomer in solid n-D2. However, investigations with solid HD give a single, sharp new line at 3621.7 cm-1, redshifted by 3.0 cm-1 from the sharp induced solid HD absorption. Comparable intensity half-lives recently observed for H atom electron spin resonance signals in solid H2 suggest trapped H atoms as the origin of substantial induced IR intensity in adjacent H2 molecules in the solid. The H atom−H2 molecule int...

Infrared spectra of phosphorus thiohydrides (HSPH2, HPS2, and HSPS2) in solid argon

Abstract: Argon/phosphine samples were reacted with discharged S 8 /Ar mixtures and the products were trapped in solid argon for infrared spectroscopic analysis. Isotopic substitution, photolysis, and annealing behavior have characterized three novel phosphorus thiohydrides: HSPH 2 , HPSS, and HSPS 2 . The chain HPSS isomer was the product of reaction between S 2 and PH radical whereas HSPS 2 was the product of reaction between S 3 and PH. There is spectroscopic evidence that HSPH radical was also trapped in the matrix

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