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.

Reactions of Laser-Ablated Aluminum Atoms with Ammonia. Infrared Spectra of HAlNH2, AlNH2, and HAlNH in Solid Argon

Abstract: Pulsed laser-ablated Al atoms react with NH3 to give two major products, HAlNH2 and AlNH2, which are trapped in solid argon and identified from infrared spectra through isotopic substitution (15N, D) and MP2 calculations of product structures and isotopic frequencies. The bent HAlNH molecule was a minor product.

Infrared spectrum of a symmetrical phosphine-ozone complex in solid argon

Abstract: Cocondensation of Ar/PH/sub 2/ and Ar/O/sub 2/ samples at 12-18 K has produced sharp satellite absorptions at 1037.3 cm/sup -1/ below nu/sub 3/ of O/sub 3/ at 1039.9 cm/sup -1/, at 988.5 and 986.3 cm/sup -1/ below nu/sub 2/ of PH/sub 3/ at 994 cm/sup -1/, and at 705.2 cm/sup -1/ above nu/sub 2/ of O/sub 3/ at 704.4 cm/sup -1/. These bands, which photolyzed with red visible light and were reproduced on sample warming to allow reagent diffusion, are assigned to the PH/sub 3/-O/sub 3/ complex. A sharp sextet in /sup 16,18/O/sub 3/ experiments indicated a symmetrical attachment of ozone in the complex. The red visible photolysis is postulated to involve a charge-transfer mechanism. 32 references, 3 figures, 2 tables.

Matrix radiolysis and photoionization of CF2Cl2 and CF3Cl. Infrared spectra of CF2Cl+ and the parent cations

Abstract: The ’’Freon’’ molecules CF2Cl2 and CF3Cl have been subjected to matrix radiolysis and photoionization during condensation with excess argon at 15 K. Infrared spectra showed stable and free radical products and new absorptions due to charged species. The molecular ion bands exhibited different behavior on filtered mercury arc photolysis. New 1415 and 1515 cm−1 absorptions decreased by 220–1000 nm photolysis are assigned to CF2Cl+2 and CF3Cl+. Other absorptions eliminated by mercury arc light, some of which were produced on photolysis of sodium–chlorofluoromethane samples, are attributed to molecular anions. The vibrational assignments were verified by carbon‐13 isotopic studies.

Noble Gas Matrices May Change the Electronic Structure of Trapped Molecules: The UO2(Ng)4 [Ng=Ne, Ar] Case

Abstract: In the last two decades matrix isolation techniques have achieved a notable success for several types of spectroscopy, ranging from infrared, optical absorption, laser-induced fluorescence and electron-spin resonance spectroscopy. Their major accomplishment lies on the possibility of embedding a guest molecule inside a host that acts as spectator and is inert towards any type of chemical interaction at very low temperatures (4–12 K). The most successful isolations occur when the gas used to trap the guest molecule is a light noble gas, known for its reluctance to form any type of chemical bond. The recent discoveries of stable noble gas complexes, such as HArF and NgAuF (Ng=Ar, Kr, Xe), have spurred new questions regarding the actual inertness of Ng hosts in matrix isolation, especially when actinide molecules, capable of forming bonds possibly involving the close-lying 5f, 6d, and 7s orbitals, are trapped. In particular, the molecules CUO and UO2 have challenged this paradigm, having shown in recent years a very probable noble-gas-induced ground state reversal going from Ne to Ar as the isolating gases. On investigating the UO2 molecule in more detail, Andrews et al. in 2000 noticed a large frequency shift for the asymmetric stretching mode at n=776 cm!1 in solid Ar, as compared to solid Ne at n=915 cm!1.[8] Such a significant shift can only be explained with the help of highly accurate calculations by exploring several electronic states and matching the measured asymmetric U!O stretch vibration with the computed ones. Following this procedure, the two possible candidates to the ground-state reversal have been recognized in the F2u (ground state in gas phase) and the H4g states, with their values being computed at n=919 and 824 cm!1, respectively, by using density functional theory (DFT). Subsequently, Heaven et al. have recorded fluorescence spectra attributed to UO2 in solid Ar and concluded that the pattern of low-lying electronic excited states is consistent with their previous gas-phase measurements, where they established the F2u as the ground state and stated that reversal of the ground state in solid Ar is unlikely. As a consequence of this contradicting situation, theoretical chemists carried out state-of-the-art calculations pinpointing the F2u state as the ground state and describing with great precision the excitation spectrum of the UO2 molecule. However, the calculations have been done for the bare molecule, certainly a good approximation for the gas phase, but not for the matrix. Now with improvement of computer architecture, we can use computationally intensive methods to study the electronic excited states of the UO2 molecule with a shell of noble gas atoms. In this work, we decided to run CASSCF/ CASPT2 calculations on the UO2(Ng)4 [Ng=Ne, Ar] complex, where the four noble gas atoms are displaced along the equatorial plane at a fixed equal U!Ng bond length, thus enforcing a D4h symmetry (D2h in the calculations). We decided to keep the inversion center to distinguish between the ungerade and gerade states and to allow maximum computational advantage. See the Supporting Information for more details. In Figure 1, the SO-CASPT2 potential energy surface (PES) computed with MOLCAS is depicted for the most [a] Prof. Dr. L. Gagliardi Department of Chemistry University of Minnesota and Supercomputing Institute 207 Pleasant St. SE, Minneapolis, MN 55455 (USA) Fax: (+1)6126 267 541 E-mail : gagliard@umn.edu [b] Dr. I. Infante Kimika Fakultatea Euskal Herriko Unibertsitatea and Donostia International Physics Center (DIPC) P.K. 1072, 20080 Donostia, Euskadi (Spain) [c] Prof. Dr. L. Andrews Department of Chemistry, University of Virginia Charlottesville, Virginia 22904-4319 (USA) [d] Dr. X. Wang Department of Chemistry, Tongji University 200092 Shanghai (China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002549.

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