Central-field intermolecular potentials from the differential elastic scattering of H2(D2) by other molecules

Differential elastic scattering cross sections for the systems H2+ O2, SF6, NH3, CO, and CH4 and for D2+ O2, SF6, and NH3 have been obtained from crossed beam studies. In all cases, rapid quantum oscillations have been resolved which permit the determination of intermolecular potential parameters if a central-field assumption is adopted. These potentials were found to be independent of both the isotopic form of the hydrogen molecule, and the relative collision energy. As a result of this, and the ability of these spherical potentials quantitatively to describe the measured scattering, it is concluded that anisotropy effects do not seem to be important in these H2(D2) systems

Femtosecond Laser Photoionization Time-of-Flight Mass Spectrometry of Nitro-aromatic Explosives and Explosives Related Compounds

The ultrafast laser-induced photoionization and photodissociation processes of the nitroaromatic containing explosive and explosive related compounds (ERCs) nitrobenzene (NB), 1,3-dinitrobenzene (DNB), m-nitrotoluene (MNT), 2,4-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT) have been investigated at three laser wavelengths and power densities using a time-of-flight mass spectrometer. Examination of the mass spectra of these compounds reveals the enhanced formation of the molecular ion [M+] when ultraviolet (332 nm) and visible (495 nm) light is used relative to infrared (795 nm) radiation. In addition, at 795 nm and a power density of 3.5 × 1014 W/cm2, the presence of a competition between multiphoton ionization (MPI) and Coulomb explosion (CE) channels is revealed by peak shape analysis, and is thought to be operative under these conditions for all of the molecules investigated

Novel mass spectrometric instrument for gaseous and particulate characterization and monitoring. Final report, September 1992--August 1994

An instrument is being developed that will be capable of providing real-time (<1 minute), quantitative, chemical analysis of gaseous and particulate pollutants generated from DOE waste cleanup activities. The instrument can detect and identify volatile organic compounds, polynuclear aromatic hydrocarbons, heavy metals, and transuranic species released during waste cleanup. It consists of an isokinetic sampler operable up to 500 K and wide flow rate range, a high- to low-pressure transition and sampling region separating particles from vapors for separate analysis, two small mass spectrometers (one for organic analysis by field ionization and one for particulate analysis by thermal pyrolysis and electron-impact ionization), and a powerful PC for control/data acquisition. Initially, the instrument will used with the K-1435 Toxic Substances Control Act (TSCA) incinerator at K-25; other applications are also possible, eg, vitrification monitoring, storage tank offgassing analysis, etc. It will be easily transportable. This report details the technical accomplishments of Phase I

Initial Development of a Continuous Emission Monitor for Dioxins

Under contract DE-AC26-98FT-40370, SRI International has completed the third phase of a planned three-phase effort to develop a laboratory prototype continuous emission monitor (CEM) for dioxins and furans generated during the incineration of waste materials at DOE remediation sites. The project was initiated on July 29, 1998 with the technical effort completed in October 2001. During this research effort, SRI has made numerous improvements in our jet-REMPI instrument. These improvements have involved characterization and optimization of the molecular cooling in the gas jet, implementation of a custom-fabricated, four pulsed valve assembly, new data acquisition and display software, and preliminary development of a wavelength and mass calibration approach. We have also measured the REMPI excitation spectra of numerous organic compounds that are likely to be present in the exhaust stream of a waste incinerator. These spectra must be well characterized in the laboratory to understand any potential interferences that might arise when monitoring for dioxin and furan congeners. Our results to date continue to validate the original concept of using jet-REMPI as the detection method in a dioxin CEM. Using only commercial components with minor modifications, we have already demonstrated a detection sensitivity in the low ppt range with sufficient chemical specificity to separately detect two closely related congeners of dichlorodibenzodioxin present in a mixture. To demonstrate the utility of this methodology outside of the controlled conditions of the laboratory, we performed a series of pseudo-field experiments at the US Environmental Protection Agency's National Risk Management Research Laboratory, Research Triangle Park, NC. The instrument used for those studies was built by SRI under contract with US EPA, and was an exact duplicate of the SRI system. This duplication allowed the experiments to be conducted without transporting the SRI system to the EPA site. Using the jet-REMPI system in conjunction with a combustion flow reactor, the joint SRI-EPA team discovered several new, and unexpected, chemical species in the exhaust stream of a pure methane flame. Based on our work in this project, we have developed a number of concepts for instrumental improvements that will substantially increase our sensitivity while maintaining the exceptional selectivity required of a dioxin CEM. In addition, we have developed several system configurations with varying degrees of functionality that can be further developed and deployed for process monitoring, surrogate measurements, and potentially, as a dioxin control CEM. Due to the extremely demanding regulatory compliance monitoring requirements involving both congener specificity and sub-part-per-trillion sensitivity with near real-time speed, we believe it is not as yet possible to specify a system configuration for a true dioxin compliance monitor. While a true TEQ compliance monitor is not yet possible using the jet-REMPI approach, the technique may prove useful as a surrogate, or indicator monitor. This application would involve continuous measurement of surrogate compounds, such as lowly chlorinated dioxins and furans, whose concentrations have been previously correlated with the TEQ. Such an instrument would not require the extreme sensitivity of a compliance monitor although the high degree of chemical selectivity would remain important

Angular scattering in electron capture and loss D/sup -/ beam formation processes

The development of high energy (> 150 keV) neutral beams for heating and fueling magnetic fusion devices depends on the ability to produce well-collimated negative ion beams. The double capture charge-exchange technique is a known, scalable method. In order to maximize the overall efficiency of the process and to achieve the desired beam characteristics, it is necessary to examine the optical qualities of the beams as well as the total efficiency of beam production. A combined modeling and experimental study of the angular scattering effects in negative ion formation and loss processes has therefore been undertaken

SARS-CoV-2 Breakthrough Infections: Incidence and Risk Factors in a Large European Multicentric Cohort of Health Workers.

Background: The research aimed to investigate the incidence of SARS-CoV-2 breakthrough infections and their determinants in a large European cohort of more than 60,000 health workers. Methods: A multicentric retrospective cohort study, involving 12 European centers, was carried out within the ORCHESTRA project, collecting data up to 18 November 2021 on fully vaccinated health workers. The cumulative incidence of SARS-CoV-2 breakthrough infections was investigated with its association with occupational and social-demographic characteristics (age, sex, job title, previous SARS-CoV-2 infection, antibody titer levels, and time from the vaccination course completion). Results: Among 64,172 health workers from 12 European health centers, 797 breakthrough infections were observed (cumulative incidence of 1.2%). The primary analysis using individual data on 8 out of 12 centers showed that age and previous infection significantly modified breakthrough infection rates. In the meta-analysis of aggregated data from all centers, previous SARS-CoV-2 infection and the standardized antibody titer were inversely related to the risk of breakthrough infection (p = 0.008 and p = 0.007, respectively). Conclusion: The inverse correlation of antibody titer with the risk of breakthrough infection supports the evidence that vaccination plays a primary role in infection prevention, especially in health workers. Cellular immunity, previous clinical conditions, and vaccination timing should be further investigated