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 chloride salts and HCl and DCl: Infrared spectra of the M+HCl2− and M+DCl2− ion pairs

Abstract: The matrix reactions of alkali metal chloride salts and HCl and DCl have been investigated in argon matrices, as well as the reaction of lithium metal with HCl and DCl. From each reaction product a single intense band was observed which has been assigned to the antisymmetric stretch ν3 of the HCl2− and DCl2− anions in the M+HCl2− and M+DCl2− ion pairs. Comparisons to literature spectra, in conjunction with quartic deuterium shifts, indicate that the anion has a linear, centrosymmetric geometry in the isolated ion pair. A rough estimate for the bond strength of the hydrogen bond in this anion is 18±2 kcal/mole. Further, comparison to the spectra of earlier workers indicates that bands previously asigned to the HCl2 radical are best reassigned to the isolated HCl2− anion.

Infrared spectra of the WH4(H2)4 complex in solid hydrogen.

Abstract: The codeposition of laser-ablated tungsten atoms with neat hydrogen at 4 K forms a single major product with a broad 2500 cm-1 and sharp 1860, 1830, 1782, 1008, 551, and 437 cm-1 absorptions, which are assigned to the WH4(H2)4 complex on the basis of isotopic shifts and agreement with isotopic frequencies calculated by density functional theory. This D2d structured complex was computed earlier to form exothermically from W atoms and hydrogen molecules. Annealing the matrix allows hydrogen to evaporate and the complex to aggregate and ultimately to decompose. Comparison of the H−H stretching mode at 2500 cm-1 and the W−H2 stretching mode at 1782 cm-1 with 2690 and 1570 cm-1 values for the Kubas complex W(CO)3(PR3)2(H2) suggests that the present physically stable WH4(H2)4 complex has more strongly bound dihydrogen ligands. Our CASPT2 calculations suggest a 15 kcal/mol average binding energy per dihydrogen molecule in the WH4(H2)4 complex.

Oxidation of phosphorus(III) halides by red photolysis of ozone complexes in solid argon

Abstract: PCl{sub 3}-O{sub 3} and PBr{sub 3}-O{sub 3} complexes in solid argon photolyze to give phosphoryl halides with red visible radiation that has no effect on isolated ozone. These observations and similar results for PH{sub 3}-O{sub 3} and P{sub 4}-O{sub 3} complexes show that the complex markedly increases the cross section for red photodissociation of ozone and suggest that this increase is due to the complex effectively lowering the barrier to dissociation by providing a strongly exothermic dissociation-recombination process.

Reactions of Laser-Ablated Chromium Atoms, Cations, and Electrons with CO in Excess Argon and Neon: Infrared Spectra and Density Functional Calculations on Neutral and Charged Unsaturated Chromium Carbonyls

Abstract: Laser-ablated Cr atoms react with CO (12C16O, 13C16O, 12C18O) in excess argon to give the same Cr(CO)3,4,5 species observed from the photodissociation of Cr(CO)6. Similar reactions in excess neon give neon matrix fundamentals between argon matrix and gas-phase values. The dicarbonyl Cr(CO)2 is bent with 1970.8, 1821.5 cm-1 and 1982.1, 1832.9 cm-1 C−O stretching fundamentals in solid argon and neon, respectively. The high-spin CrCO molecule appears at 1975.6 and 2018.4 cm-1 in solid argon and neon, respectively, and exhibits a strong matrix interaction. The CrCO+ cation and Cr(CO)2- anion are observed in laser-ablation experiments in solid neon at 2200.7 and 1705.0 cm-1, respectively. The Cr2(CO)2 complex absorbs strongly at 1735.4 cm-1 and gives several combination bands in neon. Density functional theory calculations support the vibrational 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