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Long BA, Eyet N, Williamson J, Shuman NS, Ard SG, Viggiano AA. Kinetics for the Reactions of H 3O +(H 2O) n=0-3 with Isoprene (2-Methyl-1,3-butadiene) as a Function of Temperature (300-500 K). J Phys Chem A 2022; 126:7202-7209. [PMID: 36169997 DOI: 10.1021/acs.jpca.2c05287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report kinetics studies of H3O+(H2O)n=0-3 with isoprene (2-methyl-1,3-butadiene, C5H8) as a function of temperature (300-500 K) measured using a flowing afterglow-selected ion flow tube. Results are supported by density functional (DFT) calculations at the B3LYP/def2-TZVP level. H3O+ (n = 0) reacts with isoprene near the collision limit exclusively via proton transfer to form C5H9+. The first hydrate (n = 1) also reacts at the collision limit and only the proton transfer product is observed, although hydrated protonated isoprene may have been produced and dissociated thermally. Addition of a second water (n = 2) lowers the rate constant by about a factor of 10. The proton transfer of H3O+(H2O)2 to isoprene is endothermic, but transfer of the water ligands lowers the thermicity and the likely process occurring is H3O+(H2O)2 + C5H8 → C5H9+(H2O)2 + H2O, followed by thermal dissociation of C5H9+(H2O)2. Statistical modeling indicates the amount of reactivity is consistent with the process being slightly endothermic, as is indicated by the DFT calculations. This reactivity was obscured in past experiments due to the presence of water in the reaction zone. The third hydrate is observed not to react and helps explain the past results for n = 2, as n = 2 and 3 were in equilibrium in that flow tube experiment. Very little dependence on temperature was found for the three species that did react. Finally, the C5H9+ proton transfer product further reacted with isoprene to produce mainly C6H9+ along with a small amount of clustering.
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Affiliation(s)
- Bryan A Long
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
| | - Nicole Eyet
- Chemistry Department, Saint Anselm College, Manchester, New Hampshire 03102, United States
| | - John Williamson
- Institute for Scientific Research, Boston College, Boston, Massachusetts 02467, United States
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
| | - Shaun G Ard
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
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Sawyer JC, Miller TM, Ard SG, Sweeny BC, Viggiano AA, Shuman NS. Thermal rate constants for electron attachment to N 2O: An example of endothermic attachment. J Chem Phys 2020; 153:074306. [PMID: 32828078 DOI: 10.1063/5.0016121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Rate constants for dissociative electron attachment to N2O yielding O- have been measured as a function of temperature from 400 K to 1000 K. Detailed modeling of kinetics was needed to derive the rate constants at temperatures of 700 K and higher. In the 400 K-600 K range, upper limits are given. The data from 700 K to 1000 K follow the Arrhenius equation behavior described by 2.4 × 10-8 e-0.288 eV/kT cm3 s-1. The activation energy derived from the Arrhenius plot is equal to the endothermicity of the reaction. However, calculations at the CCSD(T)/complete basis set level suggest that the lowest energy crossing between the neutral and anion surfaces lies 0.6 eV above the N2O equilibrium geometry and 0.3 eV above the endothermicity of the dissociative attachment. Kinetic modeling under this assumption is in modest agreement with the experimental data. The data are best explained by attachment occurring below the lowest energy crossing of the neutral and valence anion surfaces via vibrational Feshbach resonances.
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Affiliation(s)
- Jordan C Sawyer
- NRC Postdoc at Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Thomas M Miller
- Boston College Institute for Scientific Research, Boston, Massachusetts 02549, USA
| | - Shaun G Ard
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Brendan C Sweeny
- NRC Postdoc at Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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Marowsky G, Troe J, Viggiano AA. On the Competition Between Electron Autodetachment and Dissociation of Molecular Anions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:1828-1834. [PMID: 31140079 PMCID: PMC6805799 DOI: 10.1007/s13361-019-02237-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Revised: 04/02/2019] [Accepted: 04/22/2019] [Indexed: 06/09/2023]
Abstract
We treat the competition between autodetachment of electrons and unimolecular dissociation of excited molecular anions as a rigid-/loose-activated complex multichannel reaction system. To start, the temperature and pressure dependences under thermal excitation conditions are represented in terms of falloff curves of separated single-channel processes within the framework of unimolecular reaction kinetics. Channel couplings, caused by collisional energy transfer and "rotational channel switching" due to angular momentum effects, are introduced afterward. The importance of angular momentum considerations is stressed in addition to the usual energy treatment. Non-thermal excitation conditions, such as typical for chemical activation and complex-forming bimolecular reactions, are considered as well. The dynamics of excited SF6- anions serves as the principal example. Other anions such as CF3- and POCl3- are also discussed.
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Affiliation(s)
- Gerd Marowsky
- Laser-Laboratorium Göttingen, Hans-Adolf-Krebs-Weg 1, 37077, Göttingen, Germany
| | - Jürgen Troe
- Laser-Laboratorium Göttingen, Hans-Adolf-Krebs-Weg 1, 37077, Göttingen, Germany.
- Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, 37077, Göttingen, Germany.
- Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, 37077, Göttingen, Germany.
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Avenue SE, Bldg 570, Kirtland Air Force Base, Albuquerque, NM, 87117-5-776, USA
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Miller TM, Viggiano AA, Shuman NS. Contrast between the mechanisms for dissociative electron attachment to CH 3SCN and CH 3NCS. J Chem Phys 2018; 148:184303. [PMID: 29764146 DOI: 10.1063/1.5026802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The kinetics of thermal electron attachment to methyl thiocyanate (CH3SCN), methyl isothiocyanate (CH3NCS), and ethyl thiocyanate (C2H5SCN) were measured using flowing afterglow-Langmuir probe apparatuses at temperatures between 300 and 1000 K. CH3SCN and C2H5SCN undergo inefficient dissociative attachment to yield primarily SCN- at 300 K (k = 2 × 10-10 cm3 s-1), with increasing efficiency as temperature increases. The increase is well described by activation energies of 0.17 eV (CH3SCN) and 0.14 eV (C2H5SCN). CN- product is formed at <1% branching at 300 K, increasing to ∼30% branching at 1000 K. Attachment to CH3NCS yields exclusively SCN- ionic product but at a rate at 300 K that is below our detection threshold (k < 10-12 cm3 s-1). The rate coefficient increases rapidly with increasing temperature (k = 6 × 10-11 cm3 s-1 at 600 K), in a manner well described by an activation energy of 0.51 eV. Calculations at the B3LYP/def2-TZVPPD level suggest that attachment to CH3SCN proceeds through a dissociative state of CH3SCN-, while attachment to CH3NCS initially forms a weakly bound transient anion CH3NCS-* that isomerizes over an energetic barrier to yield SCN-. Kinetic modeling of the two systems is performed in an attempt to identify a kinetic signature differentiating the two mechanisms. The kinetic modeling reproduces the CH3NCS data only if dissociation through the transient anion is considered.
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Affiliation(s)
- Thomas M Miller
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
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Wiens JP, Martinez O, Ard SG, Sweeny BC, Viggiano AA, Shuman NS. Kinetics of Cations with C 2 Hydrofluorocarbon Radicals. J Phys Chem A 2017; 121:8061-8068. [PMID: 28949143 DOI: 10.1021/acs.jpca.7b07778] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reactions of the cations Ar+, O2+, CO2+, and CF3+ with the C2 radicals C2H5, H2C2F3, C2F3, and C2F5 were investigated using the variable electron and neutral density attachment mass spectrometry technique in a flowing afterglow-Langmuir probe apparatus at room temperature. Rate coefficients for observed product channels for these 16 reactions are reported as well as rate coefficients and product branching fractions for the 16 reactions of the same cations with each of the stable neutrals used as radical precursors (the species RI, where R is the radical studied). Reactions with the stable neutrals proceed by charge transfer at or near the collisional rate coefficient where energetically allowed; where charge transfer is endothermic, bond-breaking/bond-making chemistry occurs. While also efficient, reactions with the radicals are more likely to occur at a smaller fraction of the collisional rate coefficient, and bond-breaking/bond-making chemistry occurs even in some cases where charge transfer is exothermic. It is noted that unlike radical reactions with neutral species, which occur with rate coefficients that are generally elevated compared to those of stable species, ion-radical reactivity is generally decreased relative to that of reactions with stable species. In particular, long-range charge transfer appears more likely to be frustrated in the ion-radical systems.
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Affiliation(s)
- Justin P Wiens
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Oscar Martinez
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Shaun G Ard
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Brendan C Sweeny
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate , Kirtland AFB, New Mexico 87117, United States
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Han H, Alday B, Shuman NS, Wiens JP, Troe J, Viggiano AA, Guo H. Calculations of the active mode and energetic barrier to electron attachment to CF 3 and comparison with kinetic modeling of experimental results. Phys Chem Chem Phys 2016; 18:31064-31071. [PMID: 27808307 DOI: 10.1039/c6cp05867a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To provide a deeper understanding of the kinetics of electron attachment to CF3, the six-dimensional potential energy surfaces of both CF3 and CF3- were developed by fitting ∼3000 ab initio points per surface at the AE-CCSD(T)-F12a/AVTZ level using the permutation invariant polynomial-neural network (PIP-NN) approach. The fitted potential energy surfaces for CF3 and CF3- had root mean square fitting errors relative to the ab initio calculations of 1.2 and 1.8 cm-1, respectively. The main active mode for the crossing between the two potential energy surfaces was identified as the umbrella bending mode of CF3 in C3v symmetry. The lowest energy crossing point is located at RCF = 1.306 Å and θFCF = 113.6° with the energy of 0.051 eV above the minimum of the CF3 electronic surface. This value is only slightly larger than the experimental data 0.026 ± 0.01 eV determined by kinetic modeling of electron attachment to CF3. The small discrepancy between the theoretical and experimentally measured values is analyzed.
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Affiliation(s)
- Huixian Han
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
| | - Benjamin Alday
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA.
| | - Justin P Wiens
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA.
| | - Jürgen Troe
- Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077, Göttingen, Germany and Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, D-37077 Göttingen, Germany
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117, USA.
| | - Hua Guo
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
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Wiens JP, Shuman NS, Miller TM, Viggiano AA. Electron attachment and positive ion chemistry of monohydrogenated fluorocarbon radicals. J Chem Phys 2015; 143:074309. [PMID: 26298136 DOI: 10.1063/1.4928691] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Rate coefficients and product branching fractions for electron attachment and for reaction with Ar(+) are measured over the temperature range 300-585 K for three monohydrogenated fluorocarbon (HFC) radicals (CF3CHF, CHF2CF2, and CF3CHFCF2), as well as their five closed-shell precursors (1-HC2F4I, 2-HC2F4I, 2-HC2F4Br, 1-HC3F6I, 2-HC3F6Br). Attachment to the HFC radicals is always fairly inefficient (between 0.1% and 10% of the Vogt-Wannier capture rate), but generally faster than attachment to analogous perfluorinated carbon radicals. The primary products in all cases are HF-loss to yield C(n)F(m-1)(-) anions, with only a minor branching to F(-) product. In all cases the temperature dependences are weak. Attachment to the precursor halocarbons is near the capture rate with a slight negative temperature dependence in all cases except for 2-HC2F4Br, which is ∼10% efficient at 300 K and becomes more efficient, approaching the capture rate at higher temperatures. All attachment kinetics are successfully reproduced using a kinetic modeling approach. Reaction of the HFC radicals with Ar(+) proceeds at or near the calculated collisional rate coefficient in all cases, yielding a wide variety of product ions.
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Affiliation(s)
- Justin P Wiens
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
| | - Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
| | - Thomas M Miller
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
| | - Albert A Viggiano
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117, USA
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Shuman NS, Hunton DE, Viggiano AA. Ambient and Modified Atmospheric Ion Chemistry: From Top to Bottom. Chem Rev 2015; 115:4542-70. [DOI: 10.1021/cr5003479] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nicholas S. Shuman
- Air Force Research Laboratory,
Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
| | - Donald E. Hunton
- Air Force Research Laboratory,
Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
| | - Albert A. Viggiano
- Air Force Research Laboratory,
Space Vehicles Directorate, Kirtland Air Force Base, Albuquerque, New Mexico 87117, United States
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Shuman NS, Miller TM, Viggiano AA. Electron attachment to C2 fluorocarbon radicals at high temperature. J Chem Phys 2013; 139:184306. [PMID: 24320273 DOI: 10.1063/1.4829447] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Thermal electron attachment to the radical species C2F3 and C2F5 has been studied over the temperature range 300-890 K using the Variable Electron and Neutral Density Attachment Mass Spectrometry technique. Both radicals exclusively undergo dissociative attachment to yield F(-). The rate constant for C2F5 shows little dependence over the temperature range, remaining ~4 × 10(-9) cm(3) s(-1). The rate constant for C2F3 attachment rises steeply with temperature from 3 × 10(-11) cm(3) s(-1) at 300 K to 1 × 10(-9) cm(3) s(-1) at 890 K. The behaviors of both species at high temperature are in agreement with extrapolations previously made from data below 600 K using a recently developed kinetic modeling approach. Measurements were also made on C2F3Br and C2F5Br (used in this work as precursors to the radicals) over the same temperature range, and, for C2F5Br as a function of electron temperature. The attachment rate constants to both species rise with temperature following Arrhenius behavior. The attachment rate constant to C2F5Br falls with increasing electron temperature, in agreement with the kinetic modeling. The current data fall in line with past predictions of the kinetic modeling approach, again showing the utility of this simplified approach.
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Affiliation(s)
- Nicholas S Shuman
- Air Force Research Laboratory, Space Vehicle Directorate, Kirtland Air Force Base, New Mexico 87117, USA
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