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 of CH3CN→M, M-η2-(NC)-CH3, CH3-MNC Prepared by Reactions of Laser-Ablated Fe, Ru, and Pt Atoms with Acetonitrile in Excess Argon.

Abstract: Reactions of laser-ablated Fe, Ru, and Pt atoms with acetonitrile have been carried out in excess argon, and the products identified in the matrix spectra. CH3CN→Fe and Fe-η2-(NC)-CH3 observed in the original deposition spectra converted to CH3-FeNC on uv irradiation. CH3CN→Ru, the only product detected in the Ru system, dissociated on uv irradiation, but was partly reproduced on subsequent visible irradiation and annealing. Similar behavior was found for CH3CN→Pt. The major products (CH3-FeNC, CH3CN→Ru, and CH3CN→Pt) are the most stable constituents in the previously proposed reaction path for Group 4, 5, 6, and 7 metal atoms and acetonitrile, parallel with the previous results. The Group 8 metal π-coordination products are weakly bound complexes due to limited back-donation to the π*-orbitals of CH3CN. Calculations show that the Fe insertion product has a much less bent structure than the Ru analogue, in line with its higher s-character from the first row transition-metal to the C-Fe bond, and the group 8 metal methylidenes are not agostically distorted. The Pt to N bond in CH3CN→Pt is the strongest of all the metals we have investigated owing in large part to its higher electron affinity, which prevents nitrogen lone pair density from entering the pi* orbitals of the C-N group.

Infrared Spectra, Structure, and Bonding of the GeH3—CrH, HGe≡MoH3, and HGe≡WH3 Molecules in Solid Neon and Argon

Abstract: Laser ablated chromium, molybdenum, and tungsten atoms react with germane during condensation in excess noble gases. The chromium reaction stopped at the germyl metal hydride, molybdenum gave some hydride but mostly germylidyne, and tungsten reacted spontaneously to give only the germylidyne species. These molecules were identified by isotopic shifts, density-functional theory product energy and frequency calculations, and comparison to the analogous methane and silane reaction products. Effective bond orders for the HGe≡MoH3 and HGe≡WH3 molecules are 2.82 and 2.87 using the B3LYP density functional, and are slightly lower than their silicon and carbon analogues. Our calculated Ge≡M triple bond lengths for these simple trihydride complexes are 0.05 to 0.10 A shorter than those measured for larger group 6 organometallic complexes.

Matrix Infrared Spectra, Photochemistry and Density Functional Calculations of Cl--HCCl2, ClHCl-, Cl-ClCCl, and Cl--HCHCl Produced from CHCl3 and CH2Cl2 Exposed to Irradiation from Laser Ablation.

Abstract: Strong absorptions for Cl--HCCl2 with D and 13C isotopes were observed in the spectra of CHCl3 codeposited with laser-ablated metal atoms, cations, electrons, and vacuum ultraviolet radiation, which shows that the precursor is an effective electron scavenger. The IR spectra, isotopic shifts, and DFT calculations identified the major product as Cl--HCCl2, which is characterized by a strong, broad C-H stretching mode interacting with the overtone of the H-C-Cl bending fundamental. These absorptions decreased on subsequent annealing and photolysis treatments while the ClHCl- absorptions increased, suggesting that dissociation of the chloroform anion generates the stable symmetrical hydrogen dichloride anion as does the reaction of HCl and Cl-. A new set of strong, broad absorptions in the deposition spectra that diminished on the early annealing and photolysis are assigned to the Cl-ClCCl radical isomer. Dominant spectral features in the C-H stretching region for the experiments with CH2Cl2 are assigned to the symmetric C-H and the antisymmetric Cl-H-C-H stretching bands of the methylene chloride anion Cl--HCHCl. The stronger, broader, lower frequency bands are due to the hydrogen-bonded hydrogen stretching, and the weaker, sharper, higher frequency absorptions are due to the terminal C-H bond stretching. Similar experiments with CHBr3 produced absorptions for the analogous Br--HCBr2 and BrHBr- anions.

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