Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session PR3: Gas Phase Plasma Chemistry |
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Chair: J. P. Booth, Ecole Polytechnique Room: 305 AB |
Thursday, October 15, 2015 1:30PM - 1:45PM |
PR3.00001: Ion-molecule reactions with CF$_{3}$ radical Thomas M. Miller, Nicholas S. Shuman, Justin P. Wiens, Jordan C. Sawyer, Oscar Martinez Jr., Shaun G. Ard, Albert A. Viggiano The first measurements of reaction rate coefficients and products are reported for reactions of the radical CF$_{3}$ with Ar$^{+}$, Xe$^{+}$, O$_{2}^{+}$, NO$^{+}$, CO$_{2}^{+}$, and C$_{2}$F$_{5}^{+}$, at 300 K. The work was carried out in a fast flow of typically 1.5 Torr helium buffer gas (4{\%} argon) using the variable electron and neutral density attachment mass spectrometry (VENDAMS) technique. CF$_{3}$ was produced via dissociative electron attachment to CF$_{3}$I, resulting in CF$_{3}$ concentrations that were well-quantified because the plasma diffusion rate, the electron concentration, and the rate coefficient for attachment to CF$_{3}$I were separately measured in the experiment. The Ar$^{+} + $ CF$_{3}$ reaction was found to proceed at nearly the calculated collisional rate coefficient, yielding 90{\%} CF$_{2}^{+}$ along with CF$_{3}^{+}$. Reaction of CF$_{3}$ with C$_{2}$F$_{5}^{+}$ is slower and yields 75{\%} C$_{2}$F$_{4}^{+}$ along with CF$_{3}^{+}$. CF$_{3}$ undergoes charge transfer reaction with Xe$^{+}$, O$_{2}^{+}$, NO$^{+}$, and CO$_{2}^{+}$, yielding CF$_{3}^{+}$. Arguments will be made regarding reaction mechanisms, including the role of spin conservation. Comparisons with Ar$^{+}$ and O$_{2}^{+}$ reaction with CH$_{3}$ will be made. [Preview Abstract] |
Thursday, October 15, 2015 1:45PM - 2:00PM |
PR3.00002: Key insights into the reacting kinetics of atmospheric pressure plasmas using He$+$N2/O2/CO2/H2O/Air mixtures Tomoyuki Murakami A zero dimensional kinetic chemistry computational modeling to identify the important collisional mechanisms and the dominant species in atmospheric pressure plasmas has been developed [1]. This modeling provides an enhanced capability to tailor wide variety of reactive intermediates/species in atmospheric pressure plasmas using He$+$N2/O2/CO2/H2O/Air mixtures. The influence of the gas constituent, the gas temperature and the excitation frequency (kHz-, RF-, Pulsed-working) on the complex reacting chemical kinetics is clarified. This work also focuses on the benchmarking between the predictive outputs of this computer-based simulations and the diverse experimental diagnostics with particular emphasis on reactive oxygen/nitrogen intermediates/species. \\[4pt] [1] T. Murakami et al Plasma Sources Sci. Technol. 22(2013)015003 / 22(2013)015003 / 23(2014)025005. [Preview Abstract] |
Thursday, October 15, 2015 2:00PM - 2:15PM |
PR3.00003: Picosecond-TALIF and VUV absorption measurements of absolute atomic nitrogen densities from an RF atmospheric pressure plasma jet with He/O$_2$/N$_2$ gas mixtures Andrew West, Kari Niemi, Sandra Schr\"{o}ter, Jerome Bredin, Timo Gans, Erik Wagenaars Reactive Oxygen and Nitrogen species (RONS) from RF atmospheric pressure plasma jets (APPJs) are important in biomedical applications as well as industrial plasma processing such as surface modification. Atomic oxygen has been well studied, whereas, despite its importance in the plasma chemistry, atomic nitrogen has been somewhat neglected due to its difficulty of measurement. We present absolute densities of atomic nitrogen in APPJs operating with He/O$_2$/N$_2$ gas mixtures in open air, using picosecond Two-photon Absorption Laser Induced Fluorescence (ps-TALIF) and vacuum ultra-violet (VUV) absorption spectroscopy. In order to apply the TALIF technique in complex, He/O$_2$/N$_2$ mixtures, we needed to directly measure the collisional quenching effects using picosecond pulse widths (32ps). Traditional calculated quenching corrections, used in nanosecond TALIF, are inadequate due to a lack of quenching data for complex mixtures. Absolute values for the densities were found by calibrating against a known density of Krypton. The VUV absorption experiments were conducted on the DESIRS synchrotron beamline using a unique VUV Fourier-transform spectrometer. Atomic nitrogen densities were on the order of 10$^{20}$ m$^{-3}$ with good agreement between TALIF and VUV absorption. [Preview Abstract] |
Thursday, October 15, 2015 2:15PM - 2:30PM |
PR3.00004: Sensitivity Analysis in Complex Plasma Chemistry Models Miles Turner The purpose of a plasma chemistry model is prediction of chemical species densities, including understanding the mechanisms by which such species are formed. These aims are compromised by an uncertain knowledge of the rate constants included in the model, which directly causes uncertainty in the model predictions. We recently showed that this predictive uncertainty can be large---a factor of ten or more in some cases. There is probably no context in which a plasma chemistry model might be used where the existence of uncertainty on this scale could not be a matter of concern. A question that at once follows is: Which rate constants cause such uncertainty? In the present paper we show how this question can be answered by applying a systematic screening procedure---the so-called Morris method---to identify sensitive rate constants. We investigate the topical example of the helium-oxygen chemistry. Beginning with a model with almost four hundred reactions, we show that only about fifty rate constants materially affect the model results, and as few as ten cause most of the uncertainty. This means that the model can be improved, and the uncertainty substantially reduced, by focussing attention on this tractably small set of rate constants. [Preview Abstract] |
Thursday, October 15, 2015 2:30PM - 2:45PM |
PR3.00005: Chemical Production of Vibrationally Excited Carbon Monoxide from Carbon Vapor and Molecular Oxygen Precursors Kraig Frederickson, Ben Musci, J. William Rich, Igor Adamovich Recent results demonstrating the formation of vibrationally excited carbon monoxide from carbon vapor and molecular oxygen will be presented. Previous reaction dynamics simulations and crossed molecular beam experiments have shown that gas-phase reaction of carbon atoms and molecular oxygen produces vibrationally excited carbon monoxide. The present work examines the product distribution of this reaction in a collision dominated environment, at a pressure of several Torr. Carbon vapor is produced in an AC arc discharge in argon buffer operated at a voltage of approximately 1 kV and current of 10 A, and mixed with molecular oxygen, which may also be excited by an auxiliary RF discharge, in a flowing chemical reactor. Identification of chemical reaction products and inference of their vibrational populations is performed by comparing infrared emission spectra of the flow in the reactor, taken by a Fourier Transform IR spectrometer, with synthetic spectra. Estimates of vibrationally excited carbon monoxide concentration and relative vibrational level populations will be presented. [Preview Abstract] |
Thursday, October 15, 2015 2:45PM - 3:00PM |
PR3.00006: Hydrogen and Ethene Plasma Assisted Ignition by NS discharge at Elevated Temperatures Andrey Starikovskiy The kinetics of ignition in lean H$_{\mathrm{2}}$:O$_{\mathrm{2}}$:Ar and C$_{\mathrm{2}}$H$_{\mathrm{4}}$:O$_{\mathrm{2}}$:Ar mixtures has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected shock wave was measured with and without the discharge. It was shown that the initiation of the discharge with a specific deposited energy of 10 -- 30 mJ/cm$^{\mathrm{3}}$ leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time -- resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. Good agreement was obtained between the calculated ignition delay times and the experimental data. It follows from the analysis of the calculated results that the main mechanism of the effect of gas discharge on the ignition of hydrocarbons is the electron impact dissociation of O$_{\mathrm{2}}$ molecules in the discharge phase. Detailed kinetic mechanism for plasma assisted ignition of hydrogen and ethene is elaborated and verified. [Preview Abstract] |
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