Observation of Selectively Populated Monohalide Excited States from the Reactions of Group 3 Metal (Sc, Y, and La) Monomers and Dimers with Halogen-Containing Molecules.

The chemiluminescent reactions of the group 3 metals Sc and Y with F, Cl, Br, ClF, ICl (Sc), IBr (Y), and SF and La with F, SF, Cl, and ClF have been studied at low pressures (6 × 10 to 4 × 10 Torr) using a beam-gas arrangement and extended to the 10 Torr multiple collision pressure range. Contrary to previous reports, the observed chemiluminescent spectra are primarily attributed to emission from the metal monohalides. Extensive pressure and temperature dependence studies and high-level correlated molecular orbital theory calculations of the bond dissociation energies support this conclusion and the attribution of the chemiluminescence.

Excited Electronic State Cross Sections for Group 3 Halide and Oxide Production: Evaluating Relative Excited-State Quantum Yields.

The cross sections for excited-state formation from the reactions of the group 3 metals, Sc, Y, and La, with F and NO, are evaluated from experimental data. Detailed calibrations indicate that the cross sections for MF formation greatly exceed those for MO formation. The experimentally determined cross sections are compared to upper bounds for total reactive cross sections.

Electronically Excited Complex Formation in Magnesium Cluster-Halogen Atom Reactions.

A near ultraviolet transition of MgF has been observed in emission from the reaction between magnesium clusters, most likely Mg, and fluorine atoms. Because there is little evidence for upper-state internal excitation, the spectrum is assigned assuming that the upper state is quenched to its lowest vibrational levels. Two of possibly three ground-state vibrational frequencies, υ = 516 ± 10 cm and υ = 104 ± 10 cm, have been established.

Direct in situ nitridation of nanostructured metal oxide deposited semiconductor interfaces: tuning the response of reversibly interacting sensor sites.

Metal-oxide nanostructure-decorated extrinsic semiconductor interfaces modified through in situ nitridation greatly expand the range of sensor interface response. Select metal-oxide sites, deposited to an n-type nanopore-coated microporous interface, direct a dominant electron-transduction process for reversible chemical sensing, which minimizes chemical-bond formation. The oxides are modified to decrease their Lewis acidity through a weak interaction to form metal oxynitride sites.

Nanostructure-Directed Chemical Sensing: The IHSAB Principle and the Effect of Nitrogen and Sulfur Functionalization on Metal Oxide Decorated Interface Response.

The response matrix, as metal oxide nanostructure decorated -type semiconductor interfaces are modified through direct amination and through treatment with organic sulfides and thiols, is demonstrated. Nanostructured TiO₂, SnO, NiO and CuO ( = 1,2), in order of decreasing Lewis acidity, are deposited to a porous silicon interface to direct a dominant electron transduction process for reversible chemical sensing in the absence of significant chemical bond formation. The metal oxide sensing sites can be modified to decrease their Lewis acidity in a process appearing to substitute nitrogen or sulfur, providing a weak interaction to form the oxynitrides and oxysulfides.

Nanostructure-directed chemical sensing: The IHSAB principle and the dynamics of acid/base-interface interaction.

Nanostructure-decorated n-type semiconductor interfaces are studied in order to develop chemical sensing with nanostructured materials. We couple the tenets of acid/base chemistry with the majority charge carriers of an extrinsic semiconductor. Nanostructured islands are deposited in a process that does not require self-assembly in order to direct a dominant electron-transduction process that forms the basis for reversible chemical sensing in the absence of chemical-bond formation.

Nanostructure-driven analyte-interface electron transduction: a general approach to sensor and microreactor design.

A concept describing the nanostructure-directed dynamics of acid/base interaction and the balance between physisorption and chemisorption on an extrinsic semiconductor interface is evaluated and compared for n- and p-type semiconductors. The inverse hard/soft acid/base (IHSAB) concept, as it complements the HSAB concept, defines the nature of a dominant physisorption behavior and enables the creation of a matrix of controllable interactions. The technology results in the coupling of Lewis acid/base chemistry with the extrinsic semiconductor majority carriers.

Visible-light-driven reversible and switchable hydrophobic to hydrophilic nitrogen-doped titania surfaces: correlation with photocatalysis.

Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination.

Structures and heats of formation of simple alkaline earth metal compounds: fluorides, chlorides, oxides, and hydroxides for Be, Mg, and Ca.

Geometry parameters, frequencies, heats of formation, and bond dissociation energies are predicted for the simple alkaline earth (Be, Mg and Ca) fluorides, chlorides, oxides, and hydroxides at the coupled cluster theory [CCSD(T)] level including core-valence correlation with the aug-cc-pwCVnZ basis sets up to n = 5 in some cases. Additional corrections (scalar relativistic effects, vibrational zero-point energies, and atomic spin-orbit effects) were necessary to accurately calculate the total atomization energies and heats of formation. The calculated geometry parameters, frequencies, heats of formation, and bond dissociation energies are compared with the available experimental data.

Nanostructure-directed physisorption vs chemisorption at semiconductor interfaces: the inverse of the HSAB concept.

A concept, complementary to that of hard and soft acid-base interactions (HSAB-dominant chemisorption) and consistent with dominant physisorption to a semiconductor interface, is presented. We create a matrix of sensitivities and interactions with several basic gases. The concept, based on the reversible interaction of hard-acid surfaces with soft bases, hard-base surfaces with soft acids, or vice versa, corresponds 1) to the inverse of the HSAB concept and 2) to the selection of a combination of semiconductor interface and analyte materials, which can be used to direct a physisorbed vs chemisorbed interaction.

Study of concentration-dependent cobalt ion doping of TiO2 and TiO(2-x)Nx at the nanoscale.

Experiments with a porous sol-gel generated TiO(2) nanocolloid and its corresponding oxynitride TiO(2-x)N(x) are carried out to evaluate those transformations which accompany additional doping with transition metals. In this study, doping with cobalt (Co(ii)) ions is evaluated using a combination of core level and VB-photoelectron and optical spectroscopy, complementing data obtained from Raman spectroscopy. Raman spectroscopy suggests that cobalt doping of porous sol-gel generated anatase TiO(2) and nitridated TiO(2-x)N(x) introduces a spinel-like structure into the TiO(2) and TiO(2-x)N(x) lattices.

Hydrolysis of TiCl(4): initial steps in the production of TiO(2).

The hydrolysis of titanium tetrachloride (TiCl(4)) to produce titanium dioxide (TiO(2)) nanoparticles has been studied to provide insight into the mechanism for forming these nanoparticles. We provide calculations of the potential energy surfaces, the thermochemistry of the intermediates, and the reaction paths for the initial steps in the hydrolysis of TiCl(4). We assess the role of the titanium oxychlorides (Ti(x)O(y)Cl(z); x = 2-4, y = 1, 3-6, and z = 2, 4, 6) and their viable reaction paths.

Structures and heats of formation of simple alkali metal compounds: hydrides, chlorides, fluorides, hydroxides, and oxides for Li, Na, and K.

Geometry parameters, frequencies, heats of formation, and bond dissociation energies are predicted for simple alkali metal compounds (hydrides, chlorides, fluorides, hydroxides and oxides) of Li, Na, and K from coupled cluster theory [CCSD(T)] calculations including core-valence correlation with the aug-cc-pwCVnZ basis set (n = D, T, Q, and 5). To accurately calculate the heats of formation, the following additional correction were included: scalar relativistic effects, atomic spin-orbit effects, and vibrational zero-point energies. For calibration purposes, the properties of some of the lithium compounds were predicted with iterative triple and quadruple excitations via CCSDT and CCSDTQ.

Time-dependent density functional theory predictions of the vertical excitation energies of silanones as models for the excitation process in porous silicon.

Time-dependent density functional theory calculations with a proper treatment of the asymptotic form of the exchange-correlation potential have been performed on R(R')Si=O to predict vertical excitation energies. The species R(R')Si=O is used as a model for the binding of the -(R)Si=O chromophore to a porous silicon surface. The calculated vertical excitation energies are substantially lower than those determined previously and show that vertical excitation of the lone chromophore is possible for all types of substituents including electronegative ones with KrF laser excitation in contrast to other predictions.

Surface oxidation states in Si/SiO2 nanostructures prepared from Si/SiO2 mixtures.

Silica nanospheres have been produced by a novel technique where surface Si oxidation states can be adjusted using the ratio of metalloid ions/metalloid atoms in the starting mixture. When the proportions of Si4+/Si0 are equal in the synthesis, the resulting solid is considerably more reactive than Cab-O-Sil toward the phenol hydroxylation reaction and the surface shows an average Si oxidation state of +3. On the other hand, those silica nanospheres, produced from a mixture of Si4+/Si0 = 0.