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 and Quantum Chemical Calculations of Group 2 MO2, O2MO2, and Related Molecules

Abstract: Laser-ablated group 2 metal atoms have been reacted with O2 in condensing N2 to complement earlier Ar studies owing to different relaxation dynamics of N2 and Ar with respect to excited metal atoms and ionic product molecules. In the case of Ca + O2, the reaction in condensing Ar gives primarily the 3B2 open bent OCaO dioxide product, but the reaction in condensing N2 favors the 1A1 cyclic CaO2 peroxide species. Three fundamentals are observed with 18O and 44Ca substitution for CaO2, and isotopic frequencies are in excellent agreement with the predictions of quantum chemical calculations. Although DFT/B3LYP frequencies are slightly higher than MP2 and CASSCF values, a similar pattern is calculated. Ionic molecules interact more strongly with a nitrogen matrix than with argon, and calculations of N2MOx and ArMOx molecules can be used to explain matrix shifts. Several N2MO2 species are formed spontaneously from MO2 molecules in solid nitrogen, and a match is found for observed matrix and DFT calculated isot...

Infrared Spectra of Zn and Cd Hydride Molecules and Solids

Abstract: Laser-ablated Zn and Cd atoms react with molecular hydrogens upon condensation at 4.5 K to form the metal dihydride molecules in solid hydrogen and neon. Ultraviolet irradiation increases these absorptions by an order of magnitude. Natural zinc- and cadmium isotopic splittings are resolved in solid p-H2, o-D2, and HD. Weaker absorptions are assigned to the linear HMMH molecules and to metal cluster monohydrides with the assistance of DFT calculations. Upon sublimation of the hydrogen or neon matrix, the metal dihydride molecules polymerize into solid hydrides with broad absorption bands characteristic of hydrogen-bridge bonding.

Infrared spectra and density functional calculations of the CrO2−,MoO2−, and WO2− molecular anions in solid neon

Abstract: Laser-ablated chromium, molybdenum, and tungsten atoms react with O2 in excess neon during condensation to form the MO2 dioxide molecules as major products In addition, the MO2− anions, formed via capture of ablated electrons by the neutral molecules, were identified from isotopic splittings on their matrix infrared spectra and from density functional theory (DFT) calculations of isotopic frequencies Evidence is also presented for CrO3 and the CrO3− anion Doping with CCl4 to serve as an electron trap gave the same neutral molecules and virtually eliminated the anion absorptions, which strongly supports the anion identification

Infrared Spectra of RhCO+, RhCO, and RhCO- in Solid Neon: A Scale for Charge in Supported Rh(CO) Catalyst Systems

Abstract: Laser-ablated Rh+, Rh, and electrons react with CO on condensation in excess neon at 4 K to form RhCO+, RhCO, RhCO-, and Rh(CO)2+, Rh(CO)2, Rh(CO)2-, and higher carbonyls. These rhodium carbonyls are identified by isotopic substitution (13CO, C18O, and mixtures), electron trapping with added CCl4, and comparison with DFT calculations of isotopic frequencies. This is the first spectroscopy of isolated rhodium carbonyl cations and anions. The isolated monocarbonyl species provide a scale to estimate local charge on Rh(CO) sites in catalyst systems.

Experimental and Theoretical Evidence for the Isolation of Thorium Hydride Molecules in Argon Matrices

Abstract: The primary reaction products of laser-ablated thorium atoms with dihydrogen, ThH, ThH2, ThH3, and ThH4 have been isolated for the first time in an argon matrix and identified by the effects of isotopic substitution on their infrared spectra. DFT calculations provide firm theoretical support for the spectral assignments.

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