Electron impact dissociation of oxygen-containing molecules–A critical review

McConkey, J W; Malone, C. P.; Johnson, P. V.; Winstead, Carl; McKoy, Vincent; Kanik, I.

doi:10.1016/j.physrep.2008.05.001

Cited by 191 publications

(179 citation statements)

References 632 publications

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“…The abundance of ozone during calibration was checked by recording the QMS signal at mass number 48. Only minute trace amounts of ozone could be found, although the cross section for electron impact ionization of O 3 in the QMS ion source is higher than for O 2 (McConkey et al, 2008). Ozone is not produced directly in the discharge but in its afterglow via recombination of atomic oxygen (Normand et al, 1995).…”

Section: Uncertainties Sources Of Error and Recommendationsmentioning

confidence: 95%

“…This shift, however, affects the QMS results both for O 2 and for atomic oxygen. Their ratio is the relevant quantity for the calibration, and with an observed energy deviation of 1.5 eV the measured atomic oxygen density would be lower by 8 %, based on the literature values for electron impact ionization (Laher and Gilmore, 1990;McConkey et al, 2008). Calibration of the QMS is done by recording its readings at a series of partial pressures of O 2 and CH 4 , respectively, compared to the output from a cold cathode gauge (Pfeiffer PKR 251) with an accuracy of ±30 %.…”

Section: Uncertainties Sources Of Error and Recommendationsmentioning

confidence: 99%

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Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

et al. 2015

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Abstract. The middle-and upper-atmospheric energy budget is largely dominated by reactions involving atomic oxygen (O). Modeling of these processes requires detailed knowledge about the distribution of this oxygen species. Understanding the mutual contributions of atomic oxygen and wave motions to the atmospheric heating is the main goal of the rocket project WADIS (WAve propagation and DISsipation in the middle atmosphere). It includes, amongst others, our instruments for the measurement of atomic oxygen that have both been developed with the aim of resolving density variations on small vertical scales along the trajectory. In this paper the instrument based on catalytic effects (PHLUX: Pyrometric Heat Flux Experiment) is introduced briefly. The experiment employing solid electrolyte sensors (FIPEX: Flux φ(Phi) Probe Experiment) is presented in detail. These sensors were laboratory calibrated using a microwave plasma as a source of atomic oxygen in combination with mass spectrometer reference measurements. The spectrometer was in turn calibrated for O with a method based on methane. In order to get insight into the horizontal variability, the rocket payload had instrument decks at both ends. Each housed several sensor heads measuring during both the up-and downleg of the trajectory. The WADIS project comprises two rocket flights during different geophysical conditions. Results from WADIS-1 are presented, which was successfully launched in June 2013 from the Andøya Space Center, Norway. FIPEX data were sampled at 100 Hz and yield atomic oxygen density profiles with a vertical resolution better than 9 m. This allows density variations to be studied on very small spatial scales. Numerical simulations of the flow field around the rocket were done at several points of the trajectory to assess the influence of aerodynamic effects on the measurement results. Density profiles peak at 3 × 10 10 cm −3 at altitudes of 93.6 and 96 km for the up-and downleg, respectively.

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Section: Uncertainties Sources Of Error and Recommendationsmentioning

confidence: 95%

Section: Uncertainties Sources Of Error and Recommendationsmentioning

confidence: 99%

Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

et al. 2015

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“…This is unlikely to be a definitive assignment. Ionization cross section measurements have been made [86], but these include no data for energies less than 40 eV. We have chosen not to attempt an extrapolation into the energy range of interest in the present work, and we have instead used the theoretical results of Joshipura et al [61].…”

Section: Electron Impact Processesmentioning

confidence: 99%

Uncertainty and error in complex plasma chemistry models

Turner

2015

Plasma Sources Sci. Technol.

101

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Abstract. Chemistry models that include dozens of species and hundreds to thousands of reactions are common in low-temperature plasma physics. The rate constants used in such models are uncertain, because they are obtained from some combination of experiments and approximate theories. Since the predictions of these models are a function of the rate constants, these predictions must also be uncertain. However, systematic investigations of the influence of uncertain rate constants on model predictions are rare to non-existent. In this work we examine a particular chemistry model, for helium-oxygen plasmas. This chemistry is of topical interest because of its relevance to biomedical applications of atmospheric pressure plasmas. We trace the primary sources for every rate constant in the model, and hence associate an error bar (or equivalently, an uncertainty) with each. We then use a Monte Carlo procedure to quantify the uncertainty in predicted plasma species densities caused by the uncertainty in the rate constants. Under the conditions investigated, the range of uncertainty in most species densities is a factor of two to five. However, the uncertainty can vary strongly for different species, over time, and with other plasma conditions. There are extreme (pathological) cases where the uncertainty is more than a factor of ten. One should therefore be cautious in drawing any conclusion from plasma chemistry modelling, without first ensuring that the conclusion in question survives an examination of the related uncertainty. PACS numbers:Uncertainty and Error in Complex Plasma Chemistry Models 2

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“…Cross-sections for H 2 O and NH 3 are from Lampe et al (1957). Tetraethoxysilane (TEOS) is shown as one of the few large molecules with a measured crosssection (McConkey et al 2008). The vertical scale is relative but is normalized to two at a molecular weight of 80 because the sensitivity of the AMS is usually referenced to the nitrate ions from ammonium nitrate and a factor of about two is appropriate if roughly half of the ions from ammonium nitrate are NO 2 + or other nitrate fragments (Canagaratna et al 2007).…”

Section: Number Density In Free Molecular Flowmentioning

confidence: 99%

The effects of molecular weight and thermal decomposition on the sensitivity of a thermal desorption aerosol mass spectrometer

Murphy

2015

Aerosol Science and Technology

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In free molecular flow the slower speed of heavier molecules means that they spend more time in the ion source of a mass spectrometer. Hence the sensitivity of the thermal desorption mass spectrometers such as the Aerodyne Aerosol Mass Spectrometer (AMS) should include a term that scales as the square root of the molecular weight. Thermal decomposition on the vaporizer reduces the molecular weight prior to ionization and changes electron impact cross-sections. Thermal decomposition therefore has the potential to change the sensitivity, in some cases by more than a factor of three. Current AMS calibrations that rely upon an ammonium nitrate calibration and scaling for other components with a relative ionization efficiency may overestimate the concentration of large, thermally stable molecules and underestimate small or thermally unstable molecules. The overall sensitivity of the AMS to organics includes a partial cancellation of these effects. There is an incomplete understanding of the vaporization process, including that of ammonium nitrate.

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Electron impact dissociation of oxygen-containing molecules–A critical review

Cited by 191 publications

References 632 publications

Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

Uncertainty and error in complex plasma chemistry models

The effects of molecular weight and thermal decomposition on the sensitivity of a thermal desorption aerosol mass spectrometer

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