Peter B. Kelly

A spectroscopic study of the G 1Πg state of 7Li2 by pulsed optical–optical double resonance

The results of a pulsed optical–optical double resonance spectroscopic study of the G 1Πg state of 7Li2 are presented. Observations were made on the v*=0 through v*=20 levels, representing about 60% of the dissociation energy. A set of Dunham molecular constants was derived. The RKR potential was generated and Franck–Condon factors were determined for the range of observed vibrational levels. A dissociation energy was estimated from a Birge–Sponer extrapolation of the Gv values which suggests a correlation with the (2 2P)+(2 2P) atomic lithium states at the dissociation limit.

Subpicosecond predissociation dynamics of the methyl radical Rydberg 3 s state

The subpicosecond dissociation dynamics of the methyl radical 3 s Rydberg state have been examined using rotational resonance Raman spectroscopy. The rovibronic dependence of the excited state predissociation rates and lifetimes are obtained for the B state origin vibrational level of CH3 and CD3. Analysis of the tunneling rates using a cubic potential barrier yields estimates for the height (2200 cm−1) and position of the barrier along the dissociation coordinate (1.38 A). A comparison of the potential energy surface parameters for the Rydberg 3 s states of methyl radical and ammonia is presented.

Negative ion laser desorption ionization time-of-flight mass spectrometry of nitrated polycyclic aromatic hydrocarbons

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are widespread environmental pollutants that are generated by incomplete combustion and by atmospheric transformation of polycyclic aromatic hydrocarbons (PAHs). Many nitro-PAH compounds are potent genotoxins and some are direct acting mutagens. Detection of nitro-PAHs in aerosols is complicated by small sample sizes and nitro-PAH abundances that are 1–2 orders of magnitude less than analogous unsubstituted PAHs. Selective detection of several nitro-PAHs by using laser desorption ionization time-of-flight mass spectrometry in negative ion mode has been achieved. Desorption and ionization of nitro-PAHs were effected by using pulsed UV radiation at 266 and 213 ran. Intense molecular anions were observed in addition to fragments identified as CN− and NO2−, which were characteristic indicators of the presence of nitro-PAHs. Selective detection of nitro-PAHs in negative ion mode was demonstrated in the analysis of a diesel particulate sample.

Resonance Raman spectroscopy of the methyl radical

Abstract The first resonance Raman spectrum of the methyl radical is reported. The frequency of the symmetric stretch, ν 1 , is found to be in good agreement with previous experimental results. The overtone 2ν 1 is observed and the anharmonic constant for the symmetric stretch, X 11 , is determined. The overtone of the out of plane symmetric bend 2ν 2 is observed and confirms the negative anharmonicity for this potential obtained by Yamada et al. [J. Chem. Phys. 75 (1981) 5256].

Analysis of aerosols from the World Trade Center collapse site, New York, October 2 to October 30, 2001

The collapse of the World Trade Center (WTC) buildings #2 (South Tower), #1 (North Tower), and #7 created an enormous collapse pile which emitted intense plumes of acrid smoke and dust until roughly mid-December, when the last spontaneous surface fire occurred. We collected particles by size (8 modes, ≈12 to 0.09 micrometers diameter) and time (typical resolution of 1 to 3 h) from October 2 until late December at the EML 201 Varick Street site roughly 1.8 km NNE of the collapse site and 50 m above ground level. Here we show some of the 70,000 mass and elemental data from the time period October 2 through October 30. Identification of a WTC collapse pile source for aerosols seen at the receptor site were based upon the simultaneous presence of finely powdered concrete, gypsum, and glass with intense very fine combustion mode mass episodes concurrent with winds from the southwest quadrant. The results, derived from seven independent beam-based analytical techniques, showed that while PM10 and PM2.5 24 h values rarely, if ever, violated federal air quality standards, WTC-derived plumes swept over lower Manhattan Island, resulting in intense aerosol impacts of duration a few hours at any one site. The WTC plume resembled in many ways those seen from municipal waste incinerators and high temperatures processes in coal-fired power plants. The size fractions above 1 micrometer contained finely powdered concrete, gypsum, and glass, with sootlike coatings and anthropogenic metals, but little asbestos. Composition in the very fine size range (0.26 > Dp > 0.09 μm) was dominated by sulfuric acid and organic matter, including polycyclic aromatic hydrocarbons (PAHs) and their derivatives, and glasslike silicon-containing aerosols. Many metals were seen in this mode, most, but not all, at low concentrations. The concentrations of very fine silicon, sulfur, and many metals, as well as coarse anthropogenic metals, decreased markedly during October, probably in association with the cooling of the collapse piles. Values of very fine elements seen in May, 2002 at the WTC site were only a few percent of October values.

HOW TO CONVERT BIOLOGICAL CARBON INTO GRAPHITE FOR AMS

Isotope tracer studies, particularly radiocarbon measurements, play a key role in biological, nutritional, and environmental research. Accelerator mass spectrometry (AMS) is now the most sensitive detection method for radiocarbon, but AMS is not widely used in kinetic studies of humans. Part of the reason is the expense, but costs would decrease if AMS were used more widely. One component in the cost is sample preparation for AMS. Biological and environmental samples are commonly reduced to graphite before they are analyzed by AMS. Improvements and mechanization of this multi-step procedure is slowed by a lack of organized educational materials for AMS sample preparation that would allow new investigators to work with the technique without a substantial outlay of time and effort. We present a detailed sample preparation protocol for graphitizing biological samples for AMS and include examples of nutrition studies that have used this procedure.

Toxic combustion by-products from the incineration of chlorinated hydrocarbons and plastics

Abstract Polyvinylidene chloride and polyvinyl chloride were pyrolyzed in a thermal gravimetric analyzer and by-products were collected for chemical analysis and bioassay. Trichloroethylene was also burned in a laminar diffusion flame of methane with varying concentrations of the chlorinated compound. Soot particulates collected on filters and post-flame gases collected on sorbent tubes were extracted and analyzed using gas chromatography-mass spectrometry. Extracts were evaluated for potential toxicity using an in vitro hyperkeratinization bioassay that is sensitive to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Chemical analyses identified polycyclic aromatic hydrocarbons and chlorinated PAHs as the major pyrolysis products. Products generated from the pyrolysis of both polymers yielded definite positive bioassay responses. Most of the products obtained from the trichloroethylene flame were associated with soot particles emitted from the flame. A series of chlorinated aromatic compounds, including hexachlorocyclopentadiene and chlorinated benzenes, polycyclic aromatics, and fulvalenes were identified as major products. Dichloromethane extracts of the soots elicited a positive bioassay response.

Low-power resonant laser ablation of copper.

We emphasize two points: (l) the properties and mechanisms of very low-fluence ablation of copper surfaces and (2) the sensitivity and selectivity of resonant laser ablation (RLA). We present results for ablation of bulk copper and copper thin films; spot-size effects; the effects of surface-sample preparation and beam polarization; and an accurate measurement of material removal rates, typically ≤ 10(-3) Å at 35 mJ/cm(2). Velocity distributions were Maxwellian, with peak velocities ≈ 1-2 × 10(5) cm/s. In addition, we discuss the production of diffractionlike surface features, and the probable participation of nonthermal desorption mechanisms. RLA is shown to be a sensitive and useful diagnostic for studies of low-fluence laser-material interactions.

Resonance Raman spectrum of the allyl‐d5 radical and the force field analysis of the allyl radical

Resonance Raman spectra of the allyl‐d5 radical have been obtained with excitation between 247 and 223 nm. Analysis of the spectra yields the first observation of fundamental frequencies, ν4, ν5, and ν7 and overtone frequencies 2ν9, 2ν10, and 2ν12. The new vibrational data are combined with previously observed frequencies of allyl‐h5 and allyl‐d5 radical to produce the force field analysis for the allyl radical. This study suggests reassignment of several previously observed infrared (IR) bands. Experimental frequencies and assignments for allyl‐h5 and allyl‐d5 are compared with results from ab initio calculations. Force constants obtained in the present work are compared with the force constants of other sp2 hybridization molecules such as benzene, allene, and ethylene.

Biological/biomedical accelerator mass spectrometry targets. 1. optimizing the CO2 reduction step using zinc dust.

Biological and biomedical applications of accelerator mass spectrometry (AMS) use isotope ratio mass spectrometry to quantify minute amounts of long-lived radioisotopes such as 14C. AMS target preparation involves first the oxidation of carbon (in sample of interest) to CO2 and second the reduction of CO2 to filamentous, fluffy, fuzzy, or firm graphite-like substances that coat a −400-mesh spherical iron powder (−400MSIP) catalyst. Until now, the quality of AMS targets has been variable; consequently, they often failed to produce robust ion currents that are required for reliable, accurate, precise, and high-throughput AMS for biological/biomedical applications. Therefore, we described our optimized method for reduction of CO2 to high-quality uniform AMS targets whose morphology we visualized using scanning electron microscope pictures. Key features of our optimized method were to reduce CO2 (from a sample of interest that provided 1 mg of C) using 100 ± 1.3 mg of Zn dust, 5 ± 0.4 mg of −400MSIP, and a reduction temperature of 500 °C for 3 h. The thermodynamics of our optimized method were more favorable for production of graphite-coated iron powders (GCIP) than those of previous methods. All AMS targets from our optimized method were of 100% GCIP, the graphitization yield exceeded 90%, and δ13C was −17.9 ± 0.3‰. The GCIP reliably produced strong 12C− currents and accurate and precise Fm values. The observed Fm value for oxalic acid II NIST SRM deviated from its accepted Fm value of 1.3407 by only 0.0003 ± 0.0027 (mean ± SE, n = 32), limit of detection of 14C was 0.04 amol, and limit of quantification was 0.07 amol, and a skilled analyst can prepare as many as 270 AMS targets per day. More information on the physical (hardness/color), morphological (SEMs), and structural (FT-IR, Raman, XRD spectra) characteristics of our AMS targets that determine accurate, precise, and high-hroughput AMS measurement are in the companion paper.