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.

A further study of the products of scandium and dioxygen reactions

Abstract: The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4 additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O-2 reaction. The previously observed band at 722.5 cm(-1) is assigned as the b(2) mode of ScO2-. Bands arising from ScO+, Sc(O-2)(+), and(O-2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.

Matrix reactions of methylsilanes and oxygen atoms

Abstract: The reaction of oxygen atoms and substituted methylsilanes have been investigated in argon matrices at 14-17 K. Products were identified by using isotopic /sup 18/O/sub 3/ precursor and deuterium substitution in the Si-H bonds. With MeSiH/sub 3/, Me/sub 2/SiH/sub 2/, and Si/sub 2/H/sub 6/, the silanols MeSiH/sub 2/OH, Me/sub 2/SiHOH, and SiH/sub 3/SiH/sub 2/OH were formed, respectively. These molecules contain the Si-O-H functional group with 3708-3711-cm/sup -1/ O-H stretching frequencies. For Me/sub 4/Si, the carbinol Me/sub 3/SiCH/sub 2/OH was produced with a lower 3637-cm/sup -1/ O-H stretching frequency. Me/sub 3/SiH was different: the silanol was not observed, but instead a product tentatively identified as CH/sub 2/=Si(OH)Me was formed. Also, the silanones H/sub 2/SiO and Me(H)SiO were produced from MeSIH/sub 2/, Me(H)SiO and Me/sub 2/SiH/sub 2/ were formed with Me/sub 2/SiH/sub 2/, and Me/sub 2/SiO was again observed with Me/sub 2/SiH. These silanones contain the Si=O functional group with stretching frequencies of 1201-1209 cm/sup -1/.

Infrared spectra of cis and trans-(NO)(2)(-) anions in solid argon

Abstract: Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0 cm−1, and a band set at 1300.3, 1222.7, 884.4 cm−1. The latter bands decrease more on annealing than the 1221.0 cm−1 band. Isotopic substitution (14NO,15NO, 15N18O, and mixtures) shows that these new vibrations involve two equivalent N–O oscillators, which identifies two new (NO)2 species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm−1 band to trans-(NO)2− and the three band set to cis-(NO)2−. The observation of a weak combination band at 2492.0 cm−1 further substantiates assignment of the two N–O stretching modes in cis-(NO)2−

An infrared spectroscopic and quasirelativistic theoretical study of the coordination and activation of dinitrogen by thorium and uranium atoms

Abstract: The reactions of laser-ablated thorium and uranium metals in condensing pure dinitrogen streams as well as argon/dinitrogen mixtures have provided spectroscopic evidence for the presence of several previously uncharacterized actinide metal nitrides and dinitrogen complexes. Infrared spectra of the matrix isolated product species indicate that thorium and uranium atoms have a significant bond weakening effect on dinitrogen upon initial complexation and in some cases complete dinitrogen bond cleavage is observed. In the reactions of laser-ablated thorium and uranium atoms with pure dinitrogen, the primary products are the metal mononitride (M-N), the metal dinitride (N–M–N), and in the uranium reactions, two dinuclear products U(μ-N)2U and NU(μ-N)2U. In the reactions of thorium with dinitrogen in argon, the primary products are N–Th–N, Th(μ-N)2Th, and the dinitrogen complexes Th-η1-N2 and Th-η1:η1-(N2)2. The complete ground-state electronic structure and vibrational spectrum of each product molecule has bee...

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