title: Atmospheric pressure anion mass spectrometry: electron affinities and activation energies of thermal electron attachment - perfluoromethylcyclohexane, C7F14.
abstract: BACKGROUND
  Perfluorocarbons such as perfluoromethylcyclohexane (c-C6 F11 -CF3 ) are important man-made chemicals that have many uses including plasma processing, blood substitutes and atmospheric tracers. It is important to know the kinetics and thermodynamics of the reactions of thermal electrons with these molecules since they are potentially harmful greenhouse gases that can accumulate in the atmosphere.
  
  
  METHODS
  The least-squares fits of the temperature dependence of electron-capture detection and atmospheric pressure negative ion mass spectrometry to a kinetic model are used to determine the electron affinities of c-C6 F11 -CF3 , activation energies for the formation of c-C6 F10 -CF3 , and c-C6 F11 anions and single bond dissociation energies. These are supported by semi-empirical quantum mechanical calculations. These techniques were previously used to characterize superoxide, NO and SF6 anions.
  
  
  RESULTS
  The literature electron affinities: (eV) c-C6 F11 -CF3 , 1.06, c-C6 F10 -CF3 , 3.9, c-C6 F11 , 3.5 and D(R1-CF3 ), 3.8; D(R-F), 4.3 are supported. Additional electron affinities for c-C6 F11 -CF3 , from 0.5 to 1.5 eV are assigned to excited states. The ground state electron affinity is 3.0(2) eV from the photodetachment threshold. Pseudo one-dimensional anionic Morse potentials illustrating the mechanism for the reaction of thermal electrons with c-C6 F11 -CF3 are presented. The major anion peaks in perfluorokerosene-L are identified. An experimental setup for studying thermal electron capture reactions at variable temperatures, pressures and concentrations proposed by Herder in 2004 is presented.
  
  
  CONCLUSIONS
  There are multiple anions of c-C6 F11 -CF3 more stable than the neutral. Electron-capture detection and atmospheric pressure negative ion mass spectrometry are effective general methods for determining multiple electron affinities similar to the photodetachment, flowing afterglow, magnetron, negative surface ionization, swarm and beam procedures. Semi-empirical theoretical calculations support experimental results. Additional mass analysis studies of reactions of c-C6 F11 -CF3 with electrons over a wide range of temperatures, pressures and electron energies are desirable.
authors.affiliation: Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.|The Wentworth Foundation, 4039 Drummond, Houston, TX, 77025, USA.
authors.forename: Edward S
authors.initials: ES
authors.lastname: Chen
authors.affiliation: The Wentworth Foundation, 4039 Drummond, Houston, TX, 77025, USA.|University of Houston Clear Lake, 2700 Bay Area Blvd., Houston, TX, 77059, USA.
authors.forename: Edward C M
authors.initials: EC
authors.lastname: Chen
authors.affiliation: University of Houston Clear Lake, 2700 Bay Area Blvd., Houston, TX, 77059, USA.
authors.forename: Louis K
authors.initials: LK
authors.lastname: Barrera
authors.affiliation: The Wentworth Foundation, 4039 Drummond, Houston, TX, 77025, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Herder
mesh_terms: D001274:Atmospheric Pressure; D004583:Electrons; D005466:Fluorocarbons / Q000737:chemistry*; D016018:Least-Squares Analysis; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D008956:Models, Chemical; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005466:Fluorocarbons; C003073:perfluoromethylcyclohexane