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.

Matrix reactions of alkali metal atoms with ozone: Infrared spectra of the alkali metal ozonide molecules

Abstract: The 15°K deposition of alkali metal atoms and ozone molecules at high dilution in argon produced very intense bands near 800 cm−1 and weak bands near 600 cm−1 which showed appropriate oxygen isotopic shifts for assignment to v3 and v2 of the ozonide ion. Energetic considerations and alkali metal effects clearly indicated bonding of the metal cation to the ozonide anion. The use of scrambled isotopic ozones showed that the metal cation was symmetrically bound to the ozonide anion in a C2v structure; the symmetric interionic stretching mode was observed at 281 cm−1 for Cs+O3−. The cesium‐ozone reaction produced argon matrix fundamentals for CsO at 322 cm−1 and Cs2O at 457 cm−1; simultaneous mercury arc photolysis was required to yield the LiO absorption at 752 cm−1 from the lithium‐ozone argon matrix reaction.

FTIR spectra of ammonia clusters in noble gas matrices

Abstract: FTIR spectra of ammonia have been studied from 200 to 5200 cm−1 over a wide range of concentration and temperature conditions in solid neon, argon, and nitrogen matrices. Dimer bands appear between monomer and higher aggregate absorptions and exhibit intermediate growth behavior on sample annealing and concentration changes. Comparison of spectra in solid argon at 5 and 12 K shows unrelaxed monomer absorptions at 12 K, which almost completely vanish at 5 K without any difference in the dimer spectrum; this indicates that the NH3 submolecules are relaxed in the matrix‐isolated dimer. One antisymmetric and two symmetric N–H stretching modes were observed for the dimer, which follow the 14NH3–15NH3 and NH3–ND3 shifts of their monomer analogs. The dimer N–H stretching modes are intensified by fivefold relative to the dimer umbrella bending mode as compared to the same relative monomer band intensities, which is diagnostic of the hydrogen bonding interaction. The matrix dimer spectra show that one N–H bond fro...

Matrix reactions of silane and oxygen atoms. Infrared spectroscopic evidence for the silanol, silanone, and silanoic and silicic acid molecules

Abstract: Par photolyse, obtention de composes comportant la double liaison SiO: H 2 SiO, H(HO)SiO et (HO) 2 SiO. HSiOH est egalement prepare avec un bon rendement par decharge hyperfrequence de O 2 dans un exces d'argon. Pour les deux techniques SiH 3 OH est propose comme produit de reaction primaire par insertion d'atomes O dans une liaison SiH de SiH 4

Reactions of laser-ablated chromium atoms with dioxygen. Infrared spectra of CrO, OCrO, CrOO, CrO3,Cr(OO)2,Cr2O2,Cr2O3 and Cr2O4 in solid argon

Abstract: Reactions of laser-ablated Cr atoms with O2 gave a very strong, sharp 965.4 cm−1 band and weak, sharp 1869.7, 984.3, 914.4, 846.3, 716.2, and 643.1 cm−1 bands. The 1869.7, 965.4, and 914.4 cm−1 bands track together on annealing, show 52Cr, 53Cr, 54Cr isotopic splittings appropriate for a single Cr atom and triplets with statistical 16,18O2 for two equivalent O atoms, and are assigned to the ν1+ν3, ν3 and ν1 modes of the bent (128°±4°) chromium dioxide OCrO molecule. The 984.3 cm−1 band shows chromium isotopic splittings for two Cr atoms and 16,18O2 components for two O atoms, and is attributed to the bent CrOCrO molecule. The weak 846.3 cm−1 band exhibits proper oxygen isotopic behavior for CrO and is redshifted 39 cm−1 from the gas-phase value, the maximum shift observed for a first row transition metal monoxide. The sharp 716.2 and 643.1 cm−1 bands track together; the former reveals Cr isotopic splittings for two Cr atoms and the latter 16,18O2 splittings for two sets of dioxygen subunits; the branched-puckered-ring dimer O(Cr2O2)O is identified. Annealing produces new bands due to CrOO, CrO3, Cr(OO)2 and the ring dimers (Cr2O2) and (Cr2O2)O, which are identified from isotopic shifts and splitting patterns.

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