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.

Reactions of Laser-Ablated Ga, In, and Tl Atoms with Nitrogen Atoms and Molecules. Infrared Spectra and Density Functional Calculations of GaN, NGaN, NInN, and the M3N and MN3 Molecules

Abstract: Laser-ablated gallium atoms react with nitrogen atoms and molecules to give GaN, NGaN, Ga3N, and GaN3, which are identified from nitrogen and gallium isotopic shifts, mixed isotopic splittings, and density functional theory calculations. A 484.9 cm-1 band is assigned to the GaN molecule perturbed by the nitrogen matrix, sharp 586.4 and 584.1 cm-1 bands to the antisymmetric vibration of the linear N69GaN and N71GaN molecules, 666.2 and 656.0 cm-1 bands to the planar Ga3N molecule, and 2096.9 and 1328.3 cm-1 bands to antisymmetric and symmetric N−N−N vibrations of the GaNNN azide molecule. This work provides the first experimental evidence for GaxNy molecules that may be involved in semiconductor film growth. Laser-ablated In and Tl atom reactions produce analogous molecules.

FTIR spectra of (HF) n species in solid neon

Abstract: Condensation of Ne/HF mixtures at 5 K produces in addition to monomer HF numerous strong, sharp infrared absorptions in the 4000–3600 and 600–300 cm−1 regions and broader bands in the 3500–3100 and 1300–600 cm−1 regions. The relative absorbances of these bands depend upon concentration, spray‐on rate, and sample annealing, which are used to identify individual (HF)n species. Sharp bands at 3919, 3848, and 410 cm−1 are assigned to (HF)2. Further infrared evidence is presented for an open chain (HF)3 species. The broader bands assigned to cyclic‐(HF)n species increase at the expense of the sharper bands under conditions which favor association of HF in the matrix.

Infrared spectra of new sulfur-nitrogen species in solid argon

Abstract: New sulfur-nitrogen species were produced in an argon/nitrogen/sulfur vapor microwave discharge, and the reaction products were trapped in solid argon at 12 K. Nitrogen-15 and sulfur-34 isotopic substitutions, concentration variation, photolysis, and changes upon annealing provided a basis for identification and characterization of the new products. A product absorption at 1209.4 cm-I is identified as the diatomic SN radical. The strongest product absorption at 1225.2 cm-I, which shows a triplet and a doublet pattern with mixed sulfur and mixed nitrogen isotopes, respectively, is assigned to the antisymmetric stretching vibration of the NS2 radical; these isotopic data provide a 153 5' measure of the valence angle in NS2. The less stable NSS isomer absorbs at 1017.1 and 594.6 cm-' and is converted to NS2 with near-ultraviolet photolysis. An absorption band at 2040.2 cm-I shows quartet and doublet patterns with mixed nitrogen and sulfur isotopes, respectively, and is assigned to the nitrogen-nitrogen stretching fundamental of N2S. Evidence for higher nitrogen sulfides is also presented.

Reactions of methane with titanium atoms: CH3TiH, CH2=TiH2, agostic bonding, and (CH3)2TiH2.

Abstract: Laser-ablated titanium atoms react with methane to form the insertion product CH3TiH, which undergoes a reversible photochemical α-H transfer to give the methylidene complex CH2TiH2. On annealing a second methane activation occurs to produce (CH3)2TiH2. These molecules are identified from matrix infrared spectra by isotopic substitution (CH4, 13CH4, CD4, CH2D2) and comparison to DFT frequency calculations. The computed planar structure for singlet ground-state CH2TiH2 shows CH2 distortion and evidence for agostic bonding (H−C−Ti, 91.4°), which is supported by the spectra for CHDTiHD.

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