James B. Griffin

Guided ion beam studies of the reactions of Crn+ (n=2–18) with O2: Chromium cluster oxide and dioxide bond energies

The kinetic energy dependence of the reactions of Crn+ (n=2–18) with O2 are studied in a guided ion beam mass spectrometer. A variety of CrmO2+, CrmO+, and Crm+ product ions, where m⩽n, are observed, with the dioxide cluster ions dominating the products for all larger reactant cluster ions. Reaction efficiencies are near unity for all but the smallest clusters. The energy dependence of the product cross sections is analyzed in several different ways to determine thermochemistry for both the first and second oxygen atom binding to chromium cluster ions. These values show little dependence on cluster size for clusters larger than three atoms. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values.

Guided ion-beam studies of the reactions of Fen+ (n=1–18) with CO2: Iron cluster oxide bond energies

The kinetic energy dependence of the reactions of Fen+ (n=1–18) with CO2 are studied in a guided ion-beam mass spectrometer. The primary product ions are FenO+, which then decompose by sequential loss of iron atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Fen−1+ product ions is also observed. Large cluster ions, n⩾9, form the FenCO2+ adduct at low kinetic energies. The cross section for the primary reaction, Fen++CO2→FenO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Fen+–O bond energies are measured and found to compare well with previous measurements obtained from guided ion-beam studies of the Fen++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase values.

Guided ion beam studies of the reactions of Vn+(n=2–17) with O2: Bond energies and dissociation pathways

The kinetic energy dependence of the reactions of Vn+ (n=2–17) with oxygen is studied using a guided ion beam mass spectrometer. In all but the smallest clusters, the primary reaction process at low energies is the formation of a vanadium cluster dioxide ion which then loses one or two vanadium atoms or a vanadium oxide diatom (VO). Vanadium atom loss is the preferred reaction pathway for large clusters (n⩾5), whereas loss of VO is more favorable for the smallest reactant clusters (n⩽4). As the collision energy is increased, these primary products dissociate further by loss of additional vanadium atoms. Bond dissociation energies of the vanadium cluster oxides are determined by analysis of the kinetic energy dependence of several different products. The effect of oxygen atoms on the stabilities of vanadium cluster ions is discussed and compared with bulk phase thermochemistry.

GUIDED ION BEAM STUDIES OF THE REACTIONS OF CRN+ (N=1-18) WITH CO2: CHROMIUM CLUSTER OXIDE BOND ENERGIES

The kinetic energy dependence of the reactions of Crn+ (n=1–18) with CO2 are studied in a guided ion beam mass spectrometer. The primary product ions are CrnO+, which then decompose by sequential loss of chromium atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Crn−1+ product ions is also observed. Large cluster ions, n⩾9, form the CrnCO2+ adduct at low kinetic energies. For many cluster sizes, the cross section for the primary reaction, Crn++CO2→CrnO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Crn+–O bond energies are measured and found to compare well with measurements obtained from guided ion beam studies of the Crn++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values.

Coal Fly Ash and Mineral Dust for Toxicology and Particle Characterization Studies: Equipment and Methods for PM2.5- and PM1-Enriched Samples

Laboratory methods to produce particle samples from known, reproducible sources with sufficient mass to perform both detailed characterization and replicated in vitro toxicological assays are described. These samples are being used to study the ability of inhalable particles to produce abnormal concentrations of intracellular iron, resulting in the production of reactive oxygen species in cultured airway epithelial cells. Bulk samples of size fractionated particles from laboratory-generated coal fly ash and from simulated fugitive mining tailings and road dust were collected as surrogates for important sources of iron-bearing particles in the ambient air. An Andersen cascade impactor was used to produce particle samples enriched in three size ranges: > 10 mu m, 10-2.5 mu m, and < 2.5 mu m aerodynamic diameter. A multijet preseparator and rectangular slot virtual impactor were used to produce a fraction enriched in particles below 1 mu m. Data on the particle production conditions, production rates, and particle sample quality are provided to illustrate the feasibility of the experimental approach. The amount of iron mobilized from particles by a physiologically-relevant chelator does not correlate with the total iron. This supports the hypothesis that particle characteristics and iron speciation are important for the production of abnormal iron concentrations in cultured type A549 human airway epithelial cells. Comparison of results obtained with these surrogate particles to previous work with urban particulate standard reference materials (SRM 1648 and SRM 1649) suggests particle sources and size fractions that should be emphasized for detailed characterization of particle morphology and mineralogy.

Thermodynamics of ammonia activation by iron cluster cations: Guided ion beam studies of the reactions of Fen + (n=2-10,14) with ND3

The kinetic energy dependences of the reactions of Fen+ (n=2–10,14) with ND3 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0–10 eV. Dehydrogenation of ammonia to form FenND+ is found to be efficient and exothermic for n=4 in agreement with previous FT-ICR studies. In contrast to the ICR studies, we also observe exothermic dehydrogenation for n=3 and 5, although these processes are much less efficient than for n=4. Other clusters also undergo this process but exhibit an energy threshold. A multitude of other primary products are observed including Fen−1ND3+ (n=2–4,9,10), FenND2+ (n=1,4–8), and Fen−1ND2+ (n=2–5), which all have reaction efficiencies that depend on cluster size. At high energies, FenN+ and FenD+ are observed along with products corresponding to Fe atom loss from the primary products. Thresholds for the various primary and secondary reactions are analyzed and bond energies for iron cluster cations bound to N, ND, ND2, and ND3 are determined. Comparisons of...

Guided ion beam studies of the reactions of O+, O2+, N+ and N2+ with silane

Guided ion beam mass spectrometry is used to measure the cross sections as a function of kinetic energy for reaction of SiH4 with O+(4S), O2+ (2Πg,v=0), N+(3P), and N2+(2Σg+,v=0). All four ions react with silane by dissociative charge-transfer to form SiHm+ (m=0−3), and all but N2+ also form SiXHm+ products where (m=0−3) andX=O, O2 or N. The overall reactivity of the O+, O2+, and N+ systems show little dependence on kinetic energy, but for the case of N2+, the reaction probability and product distribution relies heavily on the kinetic energy of the system. The present results are compared with those previously reported for reactions of the rare gas ions with silane [13] and are discussed in terms of vertical ionization from the 1t2 and 3a1 bands of SiH4. Thermal reaction rates are also provided and dicussed.