Reactivity and structure of the 5-dehydro-m-xylylene anion

The electronic structure of dehydro-m-xylylene anion (DMX-) has been investigated by using chemical reactivity studies and electronic structure calculations. DMX- has been generated in the gas phase via the sequential reaction of trimethyl-3,5-bis(trimethylsilylmethyl)phenylsilane with F- and two molecules of F2. Reactivity and thermochemical properties of the ion indicate a phenyl-like anion (1a), consistent with theoretical predictions. Density functional calculations predict a nonplanar triplet anion, with an allenic singlet anion slightly higher in energy. The driving force for the out-of-plane distortion is more efficient charge delocalization that is achieved at lower symmetry.     

Fine structure of the (S(1)<--S(0)) band origins of phthalocyanine molecules in helium droplets

The laser-induced fluorescence (LIF) excitation spectra of free base phthalocyanine (Pc), Mg-Pc, and Zn-Pc molecules in superfluid helium droplets at T=0.38 K have been studied. The spectra reveal the rich vibronic structure of the S(1)<--S(0) electronic transitions. The band origins of the transitions consist of zero phonon lines accompanied by phonon wings, which originate from simultaneous electronic excitation of the molecule and excitation of the collective modes of the helium surrounding it. The phonon wings have discrete structures suggesting localization of some helium atoms in the neighborhood of the molecules. Zero phonon lines of Mg-Pc and Zn-Pc molecules are split into three components, which are separated by 0.2-0.4 cm(-1). Possible mechanism of splitting involves static or dynamic Jahn-Teller interaction of metal-phthalocyanine molecules in the twofold degenerate S(1)((1)E(u)) state with the helium shell.     

Dynamics of Impulse-Loaded Beam with One-Sided Support Ties

International Applied Mechanics - The pulsed deformation of a beam with hinged ends and discretely elastically supported span is considered. It is assumed that due to separation of the beam from...     

Transformation of a plane wave by a periodically time modulated dielectric medium

The problem of the transformation of a plane monochromatic wave by a finite-duration sequence of periodic rectangular pulses of the dielectric permittivity and magnetic permeability is solved exactly with integral equations. The expressions for the transformed component of the electric field at any point in space at an arbitrary time are derived and analyzed.     

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Advances in methods and algorithms in a modern quantum chemistry program package

Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.     

Infrared spectra and intensities of the H2O and N2 complexes in the range of the nu1- and nu3-bands of water

The IR spectra of complexes of water with nitrogen molecules in the range of the symmetric (nu(1)) and antisymmetric (nu(3)) bands of H(2)O have been studied in helium droplets. The infrared intensities of the nu(3) and nu(1) modes of H(2)O were found to be larger by factors of 1.3 and 2, respectively, in the N(2)-H(2)O complexes. These factors are smaller than those obtained in recent theoretical calculations. The conformation of the N(2)-H(2)O complex was estimated. Spectra and IR intensities of the (N(2))(2)-H(2)O and N(2)-(H(2)O)(2) complexes were also obtained and their structures are discussed.     

Evolution of the vibrational spectrum of ammonia from single molecule to bulk

Ammonia clusters (NH3)n (n=2-10(4)) have been assembled inside helium droplets and studied via infrared laser spectroscopy. The studied spectral range of 3100-3500 cm(-1) covers the nu1 and nu3 fundamental stretching bands as well as the 2nu4 overtone of the bend of ammonia molecules. The results show strong coupling of the 2nu4 overtone with the fundamental vibrations for all cluster sizes except dimers. The intensity of the nu3 band relative to the total intensity in the spectrum increases from about 30% to about 80% upon increase of the average cluster size from n=5 to n=10(4). We attributed this effect to the concomitant decrease in the fraction of the surface molecules. The results indicate that ammonia clusters obtained in He droplets have a compact structure and that inner molecules in the clusters have similar hydrogen-bonded coordination as in the crystalline form of ammonia. This surprising result is ascribed to a directionality of the hydrogen bond, which guides the low temperature growth of the cluster in He droplets.