Publications
106 results found
Townley-Smith K, Nave G, Pickering JC, et al., 2016, Hyperfine structure constants for singly ionized manganese (Mn II) using Fourier transform spectroscopy, Monthly Notices of the Royal Astronomical Society, Vol: 461, Pages: 73-78, ISSN: 0035-8711
We expand on the comprehensive study of hyperfine structure (HFS) in Mn II conducted byHolt et al. (1999) by verifying hyperfine magnetic dipole constants (A) for 20 levels previouslymeasured by Holt et al. (1999) and deriving A constants for 47 previously unstudied levels. TheHFS patterns were measured in archival spectra from Fourier transform (FT) spectrometers atImperial College London and the National Institute of Standards and Technology. Analysis ofthe FT spectra was carried out in XGREMLIN. Our A constant for the ground level has a loweruncertainty by a factor of 6 than that of Blackwell-Whitehead et al.
Mushtaq S, Steers EBM, Hoffmann V, et al., 2016, Evidence for charge transfer from hydrogen molecular ions to copper atoms in a neon-hydrogen analytical glow discharge, Journal of Analytical Atomic Spectrometry, Vol: 31, Pages: 2175-2181, ISSN: 1364-5544
Extensive investigations have been carried out in recent years on the effects of the presence of small amounts of molecular gases in analytical glow discharges (GDs) using argon as the plasma gas. Complementary studies using neon have shown that, when hydrogen is added to a neon discharge with a copper sample, the intensities of lines from most of the upper energy levels in the Cu II 3d9(2D)4p sub-configuration decrease. However, the 224.700 nm spectral line and other lines from the same upper level (3Po2) increase in intensity and this effect cannot be produced by the excitation processes normally considered. We show that asymmetric charge transfer (ACT) excitation by hydrogen molecules (H2-ACT) is the most likely explanation, the first time this process has been reported for any element in analytical GDs. We also explain why a similar effect is not observed with added nitrogen, although the ionization energies of hydrogen and nitrogen molecules are very similar.
Holmes CE, Pickering JC, Ruffoni MP, et al., 2016, EXPERIMENTALLY MEASURED RADIATIVE LIFETIMES AND OSCILLATOR STRENGTHS IN NEUTRAL VANADIUM, Astrophysical Journal Supplement Series, Vol: 224, ISSN: 1538-4365
We report a new study of the V i atom using a combination of time-resolved laser-induced fluorescence and Fourier transform spectroscopy that contains newly measured radiative lifetimes for 25 levels between 24,648 cm−1 and 37,518 cm−1 and oscillator strengths for 208 lines between 3040 and 20000 Å from 39 upper energy levels. Thirteen of these oscillator strengths have not been reported previously. This work was conducted independently of the recent studies of neutral vanadium lifetimes and oscillator strengths carried out by Den Hartog et al. and Lawler et al., and thus serves as a means to verify those measurements. Where our data overlap with their data, we generally find extremely good agreement in both level lifetimes and oscillator strengths. However, we also find evidence that Lawler et al. have systematically underestimated oscillator strengths for lines in the region of 9000 ± 100 Å. We suggest a correction of 0.18 ± 0.03 dex for these values to bring them into agreement with our results and those of Whaling et al. We also report new measurements of hyperfine structure splitting factors for three odd levels of V i lying between 24,700 and 28,400 cm−1.
Smillie DG, Pickering JC, Nave G, et al., 2016, The spectrum and term analysis of Co iii measured using Fourier transforms and grating spectroscopy, Astrophysical Journal Supplement Series, Vol: 223, ISSN: 1538-4365
The spectrum of Co iii has been recorded in the region 1562–2564 Å (64,000 cm−1–39,000 cm−1) by Fourier transform (FT) spectroscopy, and in the region 1317–2500 Å (164,000 cm−1–40,000 cm−1) using a 10.7 m grating spectrograph with phosphor image plate detectors. The spectrum was excited in a cobalt–neon Penning discharge lamp. We classified 514 Co iii lines measured using FT spectroscopy, the strongest having wavenumber uncertainties approaching 0.004 cm−1 (approximately 0.2 mÅ at 2000 Å, or 1 part in 107), and 240 lines measured with grating spectroscopy with uncertainties between 5 and 10 mÅ. The wavelength calibration of 790 lines of Raassen & Ortí Ortin and 87 lines from Shenstone has been revised and combined with our measurements to optimize the values of all but one of the 288 previously reported energy levels. Order of magnitude reductions in uncertainty for almost two-thirds of the 3d64s and almost half of the 3d64p revised energy levels are obtained. Ritz wavelengths have been calculated for an additional 100 forbidden lines. Eigenvector percentage compositions for the energy levels and predicted oscillator strengths have been calculated using the Cowan code.
Weiss Z, Steers EBM, Mushtaq S, et al., 2016, The use of radiative transition rates to study the changes in the excitation of Cu ions in a Ne glow discharge caused by small additions of H-2, O-2 and N-2, Spectrochimica Acta Part B: Atomic Spectroscopy, Vol: 118, Pages: 81-89, ISSN: 1873-3565
The excitation of Cu+ ions in a Ne glow discharge with small additions of H2, O2 and N2 was studied. Ratios of radiative transition rates between different Cu II levels in a discharge in neon, with and without the molecular gas added, were calculated, and the formalism of transition rate ratio (TRR) diagrams was developed and used to study the changing excitation conditions. Virtually no changes in the excitation of Cu+ ions occur in a neon discharge if nitrogen is added. Additions of hydrogen and oxygen to neon as the discharge gas affect excitation of the 4d, 5s and some other Cu II levels in the vicinity of the ionization energy of neon (21.56 eV). Also some lower Cu II levels, excited by radiative decay of those higher energy levels, are affected. The 4p 3P2 level at 15.96 eV is enhanced by additions of hydrogen. It was suggested that this enhancement is caused by the asymmetric charge transfer reaction between neutral copper atoms and the H2+ molecular ions.
Mushtaq S, Steers EBM, Churchill G, et al., 2016, Does asymmetric charge transfer play an important role as an ionization mode in low power-low pressure glow discharge mass spectrometry?, Spectrochimica Acta Part B-Atomic Spectroscopy, Vol: 118, Pages: 56-61, ISSN: 0584-8547
Weiss Z, Steers EBM, Pickering JC, 2015, Transition rates and transition rate diagrams in atomic emission spectroscopy: A review, SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 110, Pages: 79-90, ISSN: 0584-8547
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- Citations: 18
Heiter U, Lind K, Asplund M, et al., 2015, Atomic and molecular data for optical stellar spectroscopy, PHYSICA SCRIPTA, Vol: 90, ISSN: 0031-8949
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- Citations: 118
Fox C, Green PD, Pickering JC, et al., 2015, Analysis of far-infrared spectral radiance observations of the water vapor continuum in the Arctic, JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, Vol: 155, Pages: 57-65, ISSN: 0022-4073
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- Citations: 9
Mushtaq S, Steers EBM, Whitby JA, et al., 2015, A glow discharge time-of-flight mass spectrometry (GD-TOFMS) study of the 'hydrogen effect' using copper, iron and titanium cathodes, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 30, Pages: 1774-1781, ISSN: 0267-9477
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- Citations: 6
Den Hartog EA, Ruffoni MP, Lawler JE, et al., 2014, Fe I oscillator strengths for transitions from high-lying even-parity levels, Astrophysical Journal Supplement Series, Vol: 215, Pages: 1-13, ISSN: 0067-0049
New radiative lifetimes, measured to ±5% accuracy, are reported for 31 even-parity levels of Fe I ranging from 45061 cm–1 to 56842 cm–1. These lifetimes have been measured using single-step and two-step time-resolved laser-induced fluorescence on a slow atomic beam of iron atoms. Branching fractions have been attempted for all of these levels, and completed for 20 levels. This set of levels represents an extension of the collaborative work reported in Ruffoni et al. The radiative lifetimes combined with the branching fractions yields new oscillator strengths for 203 lines of Fe I. Utilizing a 1D-LTE model of the solar photosphere, spectral syntheses for a subset of these lines which are unblended in the solar spectrum yields a mean iron abundance of langlog[ε(Fe)]rang = 7.45 ± 0.06.
Mushtaq S, Steers EBM, Pickering JC, et al., 2014, Effect of small quantities of oxygen in a neon glow discharge, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 29, Pages: 2027-2041, ISSN: 0267-9477
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- Citations: 12
Weiss Z, Steers EBM, Pickering JC, et al., 2014, Excitation and transition rate diagrams of singly ionized iron in analytical glow discharges in argon, neon and an argon-hydrogen mixture, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 29, Pages: 2078-2090, ISSN: 0267-9477
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- Citations: 11
Mushtaq S, Steers EBM, Pickering JC, et al., 2014, Enhancement of analyte atomic lines with excitation energies of about 5 eV in the presence of molecular gases in analytical glow discharges, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 29, Pages: 2022-2026, ISSN: 0267-9477
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- Citations: 8
Ruffoni MP, Den Hartog EA, Lawler JE, et al., 2014, Fe i oscillator strengths for the Gaia-ESO survey, Monthly Notices of the Royal Astronomical Society, Vol: 441, Pages: 3127-3136, ISSN: 0035-8711
The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale study of multi-element chemical abundances of some 100 000 stars in the Milky Way with the ultimate aim of quantifying the formation history and evolution of young, mature and ancient Galactic populations. However, in preparing for the analysis of GES spectra, it has been noted that atomic oscillator strengths of important Fe I lines required to correctly model stellar line intensities are missing from the atomic data base. Here, we present new experimental oscillator strengths derived from branching fractions and level lifetimes, for 142 transitions of Fe I between 3526 and 10 864 Å, of which at least 38 are urgently needed by GES. We also assess the impact of these new data on solar spectral synthesis and demonstrate that for 36 lines that appear unblended in the Sun, Fe abundance measurements yield a small line-by-line scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with recent publications.
Weiss Z, Steers EBM, Pickering JC, et al., 2014, Transition rate diagrams - A new approach to the study of selective excitation processes: The spectrum of manganese in a Grimm-type glow discharge, SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 92, Pages: 70-83, ISSN: 0584-8547
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- Citations: 13
Weiss Z, Steers EBM, Pickering JC, et al., 2014, Excitation of higher levels of singly charged copper ions in argon and neon glow discharges, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 29, Pages: 2256-2261, ISSN: 0267-9477
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- Citations: 9
Mushtaq S, Steers EBM, Pickering JC, et al., 2013, Selective and non-selective excitation/ionization processes in analytical glow discharges: excitation of the ionic spectra in argon/helium mixed plasmas, Journal of Analytical Atomic Spectrometry
The increasing use of mixed gases, including helium mixtures, in glow discharge mass spectrometry has led to a need to understand the resulting signal enhancements due to changes in excitation and ionization processes. To understand more fully these processes in glow discharge, we have carried out complementary optical emission spectrometry experiments. The presence of added gases in the plasma gas can cause major changes in the number density of plasma gas ions and metastable atoms and so affects the intensities of spectral lines involving selective and non-selective excitation & ionization processes. We report the results of an experimental investigation on the effect of Ar/He mixed plasmas on the relative emission intensities of various analyte materials including copper, iron and titanium. Selective and non-selective excitation processes which are mainly dependent on the nature of the plasma gas and analyte material are observed and discussed.
Ruffoni MP, Allende Prieto C, Nave G, et al., 2013, INFRARED LABORATORY OSCILLATOR STRENGTHS OF Fe I IN THE <i>H</i>-BAND, ASTROPHYSICAL JOURNAL, Vol: 779, ISSN: 0004-637X
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- Citations: 20
Ruffoni MP, Pickering JC, 2013, ACCURATE RITZ WAVELENGTHS OF PARITY-FORBIDDEN [Co II] AND [V II] LINES OF ASTROPHYSICAL INTEREST, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 207, ISSN: 0067-0049
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- Citations: 3
Thorne AP, Pickering JC, Semeniuk JI, 2013, THE SPECTRUM AND TERM ANALYSIS OF V II, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 207, ISSN: 0067-0049
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- Citations: 14
Green PD, Newman SM, Beeby RJ, et al., 2012, Recent advances in measurement of the water vapour continuum in the far-infrared spectral region, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 370, Pages: 2637-2655, ISSN: 1364-503X
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- Citations: 24
Mushtaq S, Steers EBM, Pickering JC, et al., 2012, Asymmetric charge transfer involving the ions of added gases (oxygen or hydrogen) in Grimm-type glow discharges in argon or neon, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 27, Pages: 1264-1273, ISSN: 0267-9477
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- Citations: 12
Mushtaq S, Hoffmann V, Steers EBM, et al., 2012, Comparison of a sample containing oxide with a pure sample with argon-oxygen mixtures, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 27, Pages: 1423-1431, ISSN: 0267-9477
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- Citations: 17
Blackie D, Murray JE, Blackwell-Whitehead R, et al., 2011, A zero-dispersion monochromator and two-beam output for UV Fourier transform absorption spectrometry, JOURNAL OF INSTRUMENTATION, Vol: 6, ISSN: 1748-0221
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- Citations: 1
Pickering JC, Blackwell-Whitehead R, Thorne AP, et al., 2011, Laboratory measurements of oscillator strengths and their astrophysical applications, CANADIAN JOURNAL OF PHYSICS, Vol: 89, Pages: 387-393, ISSN: 0008-4204
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- Citations: 18
Blackie D, Blackwell-Whitehead R, Stark G, et al., 2011, High-resolution photoabsorption cross-section measurements of SO<sub>2</sub> at 198 K from 213 to 325 nm, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 116, ISSN: 2169-9097
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- Citations: 29
Thorne AP, Pickering JC, Semeniuk J, 2011, THE SPECTRUM AND TERM ANALYSIS OF V I, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 192, ISSN: 0067-0049
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- Citations: 25
Blackwell-Whitehead R, Pavlenko YV, Nave G, et al., 2011, Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool dwarfs, ASTRONOMY & ASTROPHYSICS, Vol: 525, ISSN: 0004-6361
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- Citations: 10
Mushtaq S, Pickering JC, Steers EBM, et al., 2011, The role of oxygen in analytical glow discharges: GD-OES and GD-ToF-MS studies, JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 26, Pages: 1746-1755, ISSN: 0267-9477
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- Citations: 18
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