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Stephan E. Barlow

Bio: Stephan E. Barlow is an academic researcher from Pacific Northwest National Laboratory. The author has contributed to research in topics: Ion & Ion cyclotron resonance. The author has an hindex of 26, co-authored 55 publications receiving 2500 citations. Previous affiliations of Stephan E. Barlow include National Institute of Standards and Technology & University of Colorado Boulder.


Papers
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Journal ArticleDOI
TL;DR: Negative ion photoelectron spectroscopy and gas-phase proton transfer kinetics were employed to determine the CH bond dissociation energies of acetylene, ethylene, and vinyl radical.
Abstract: Negative ion photoelectron spectroscopy and gas-phase proton transfer kinetics were employed to determine the CH bond dissociation energies of acetylene, ethylene, and vinyl radical: Do(HCC-H) = 131.3 f 0.7 kcal mol-', Do(CH2CH-H) = 109.7 f 0.8 kcal mol-', and Do(CH2C-H) = 81.0 f 3.5 kcal mol-'. The strengths of each of the other CH and CC bonds in acetylene and ethylene and their fragments were derived. The energy required to isomerize acetylene to vinylidene was also determined: HCWH - H2C=C: AHbo = 47.4 f 4.0 kcal mol-'. As part of this study, proton transfer kinetics in a flowing afterglow/selected-ion flow tube apparatus were used to refine the acidities of ethylene, acetylene, and vinyl. The gas-phase acidity of acetylene was tied to the precisely known values for hydrogen fluoride, AGsdd298(HF) = 365.6 f 0.2 kcal mol-', and water, AG-(H20) = 383.9 f 0.3 kcal mor', yielding AG-(HCC-H) = 369.8 f 0.6 kcal mol-'. The gas-phase acidity equilibria of acetylene with isopropyl alcohol and terr-butyl alcohol were also measured. Combined with relative acidities from the literature, these measurements yielded improved acidities for the alcohols, AGad,298( (CH3)2CHO-H) = 370.1 f 0.6 kcal mol-', AGaa298((CH3)3CO-H) = 369.3 f 0.6 kcal mol-', hGadd,298(C2HSO-H) = 372.0 f 0.6 kcal mol-', and AGacid.298(CH30-H) = 375.1 f 0.6 kcal mol-'. The gas-phase acidity of ethylene was measured relative to ammonia, AGacid.298(NH3) = 396.5 f 0.4 kcal mol-', giving AGadJ98(C2H1) = 401.0 f 0.5 kcal mol-'. The gas-phase acidity of vinyl radical was bracketed, 375.1 f 0.6 kcal mol-' I AGaaB8(CH2C-H) I 380.4 f 0.3 kcal mol-'. The electron affinities of ethynyl, vinyl, and vinylidene radicals were determined by photoelectron spectroscopy: EA(HCC) = 2.969 f 0.010 eV, EA(CH2CH) = 0.667 f 0.024 eV, and EA(CH2C) = 0.490 f 0.006 eV.

373 citations

Journal ArticleDOI
TL;DR: In this article, a theory of ion space charge influence on the observed ion cyclotron resonance frequency in static field ion traps is presented, and the dependence of this influence on ion density, ion cloud shape, and trapping geometry is investigated.

204 citations

Journal ArticleDOI
TL;DR: In this paper, a magnetic-bottle time-of-flight (TOF) photoelectron spectrometer coupled with an electrospray ionization source is developed for the investigation of multiply charged anions in the gas phase.
Abstract: A magnetic-bottle time-of-flight (TOF) photoelectron spectrometer, coupled with an electrospray ionization source, has been developed for the investigation of multiply charged anions in the gas phase. Anions formed in the electrospray source are guided by a radio-frequency quadrupole ion guide into a quadrupole ion trap, where the ions are accumulated. A unique feature of this apparatus involves the coupling of a TOF mass spectrometer to the ion trap with perpendicular ion extraction. The ion trap significantly improves the duty cycle of the experiments and allows photodetachment experiments to be performed with low repetition-rate lasers (10–20 Hz). This novel combination makes the photodetachment photoelectron spectroscopy studies of multiply charged anions possible for the first time. Furthermore, the perpendicular extraction of ions, pulsed out of the ion trap, to the TOF mass spectrometer allows the ion energies to be conveniently referenced to ground, simplifying the configuration of the TOF mass sp...

191 citations

Journal ArticleDOI
TL;DR: In this article, the authors report the first accuracy evaluation of NIST-F2, a second-generation laser-cooled caesium fountain primary standard developed at the National Institute of Standards and Technology (NIST) with a cryogenic (liquid nitrogen) microwave cavity and flight region.
Abstract: We report the first accuracy evaluation of NIST-F2, a second-generation laser-cooled caesium fountain primary standard developed at the National Institute of Standards and Technology (NIST) with a cryogenic (liquid nitrogen) microwave cavity and flight region. The 80?K atom interrogation environment reduces the uncertainty due to the blackbody radiation shift by more than a factor of 50. Also, the Ramsey microwave cavity exhibits a high quality factor (>50?000) at this low temperature, resulting in a reduced distributed cavity phase shift. NIST-F2 has undergone many tests and improvements since we first began operation in 2008. In the last few years NIST-F2 has been compared against a NIST maser time scale and NIST-F1 (the US primary frequency standard) as part of in-house accuracy evaluations. We report the results of nine in-house comparisons since 2010 with a focus on the most recent accuracy evaluation. This paper discusses the design of the physics package, the laser and optics systems and the accuracy evaluation methods. The type B fractional uncertainty of NIST-F2 is shown to be 0.11???10?15 and is dominated by microwave amplitude dependent effects. The most recent evaluation (August 2013) had a statistical (type A) fractional uncertainty of 0.44???10?15.

184 citations

Journal ArticleDOI
TL;DR: In this paper, the design of a new tandem flowing afterglow-SIFT-drift instrument which provides high sensitivity, resolution, and chemical versatility is described, and the performance of the instrument is evaluated in terms of the intensity and variety of ions which can be generated, mass-selected, and injected; the efficiency of the dual annulus SIFT injector as a venturi inlet; and reliability of the kinetic data.

163 citations


Cited by
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Journal ArticleDOI
TL;DR: The Gaussian-2 theoretical procedure (G2 theory) as discussed by the authors was proposed to calculate molecular energies (atomization energies, ionization potentials, and electron affinities) of compounds containing first and second-row atoms.
Abstract: The Gaussian‐2 theoretical procedure (G2 theory), based on a b i n i t i o molecular orbital theory, for calculation of molecular energies (atomization energies, ionization potentials,electron affinities, and proton affinities) of compounds containing first‐ (Li–F) and second‐row atoms (Na–Cl) is presented. This new theoretical procedure adds three features to G1 theory [J. Chem. Phys. 9 0, 5622 (1989)] including a correction for nonadditivity of diffuse‐s p and 2d f basis set extensions, a basis set extension containing a third d function on nonhydrogen and a second p function on hydrogen atoms, and a modification of the higher level correction. G2 theory is a significant improvement over G1 theory because it eliminates a number of deficiencies present in G1 theory. Of particular importance is the improvement in atomization energies of ionic molecules such as LiF and hydrides such as C2H6, NH3, N2H4, H2O2, and CH3SH. The average absolute deviation from experiment of atomization energies of 39 first‐row compounds is reduced from 1.42 to 0.92 kcal/mol. In addition, G2 theory gives improved performance for hypervalent species and electron affinities of second‐row species (the average deviation from experiment of electron affinities of second‐row species is reduced from 1.94 to 1.08 kcal/mol). Finally, G2 atomization energies for another 43 molecules, not previously studied with G1 theory, many of which have uncertain experimental data, are presented and differences with experiment are assessed.

3,216 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the history, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications and discuss the applications of these discharges.
Abstract: Dielectric-barrier discharges (silent discharges) are used on a large industrial scale. They combine the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. A prominent feature is the simple scalability from small laboratory reactors to large industrial installations with megawatt input powers. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and 500 kPa. Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, ultraviolet excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions the discharge can have pronounced filamentary structure or fairly diffuse appearance. History, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications are discussed in detail.

2,730 citations

Journal ArticleDOI
TL;DR: In this paper, a list of reliable bond energies that are based on a set of critically evaluated experiments is provided and a brief description of the three most important experimental techniques for measuring bond energies is provided.
Abstract: In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

2,415 citations

Journal Article
TL;DR: This Account presents a list of reliable bond energies that are based on a set of critically evaluated experiments and demonstrates how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.
Abstract: In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

1,869 citations

01 Sep 1994
TL;DR: In this article, the authors present a review of Charged Particle Dynamics and Focusing Systems without Space Charge, including Linear Beam Optics with Space Charge and Self-Consistent Theory of Beams.
Abstract: Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

1,311 citations