Hyperfine electron affinities of molecular oxygen

Electron affinities from gas chromatography electron capture detector and negative ion mass spectrometry responses and complementary methods

The use of the electron-capture detector, ECD, to measure molecular electron affinities and kinetic parameters for reactions of thermal electrons with molecules at atmospheric pressure separated by chromatography and the sensitive and selective quantitative analysis of certain classes molecules are reviewed. The evaluated ground state electron affinities of the main group elements and diatomic molecules from slightly positive, 0+, to 3.6 eV are summarized. The electron affinities of twenty-seven superoxide states determined from pulsed discharge ECD and other methods are used to calculate one dimensional potential energy curves in agreement with theory. Advances in literature searches have uncovered ECD data in dissertations and theses and in the Russian and Japanese literature. These data, unpublished radioactive and pulsed discharge ECD thermal data from the University of Houston laboratories are used to report and evaluate electron affinities. The accuracy and precision of ECD electron affinities of organic molecules are identified and tabulated so that they can be added to compilations. A procedure for calculating the temperature dependence of electron molecule reactions is presented using kinetic and thermodynamic data. These are used toselect the most appropriate equipment and conditions for ECD analyses and physical determinations.

Mass spectrometric determination of Morse parameters for the fifty-four superoxide states dissociating to the lowest limit

RATIONALE

Superoxide is the most significant homonuclear diatomic anion in biochemistry. Theory predicts 12 doublet (X, A-K) and 12 quartet (a-l) electronic states split by spin orbital coupling into 54 states dissociating to the (3) P(O) + (2) P(O(-) ) limit. Dissociation energies for the 27 bonding states with positive electron affinities have been determined from mass spectrometric data. However, the 27 antibonding states with negative electron affinities have not been experimentally characterized.

METHODS

The electron affinity of the hydrogen atom per electron, the Hylleraas, is the fundamental measure of electron correlation. It has been used to assign and evaluate experimental electron affinities of atoms and diatomic molecules. The 27 negative electron affinities of oxygen are estimated from the 27 positive values and the Hylleraas. These values are used to determine frequencies and internuclear separations by fitting theoretical electron impact distributions to the gas-phase mass spectrometric atomic oxygen anion distribution peaking at about 6.5 eV.

RESULTS

The dissociation energies, internuclear distances and frequencies giving the first complete set of Morse potential energy curves for the 54 superoxide states dissociating to the lowest limit are reported from mass spectrometric data. The potentials are compared to theoretical and empirical literature curves.

CONCLUSIONS

The existence of the 27 bonding and 27 antibonding spin orbital coupling superoxide states dissociating to (3) P(O) + (2) P(O(-) ) is established from mass analyzed thermal, photon, and electron ionization data. There are electron affinities from 0 to 0.15 eV, and onsets and peaks for dissociative electron attachment that cannot be explained by the 54 states. These support the existence of the 36 superoxide spin states dissociating to [(1) D(O) + (2) P(O(-) )] and [(1) S(O) + (2) P(O(-) )] predicted by quantum mechanics. Copyright © 2016 John Wiley & Sons, Ltd.

Atmospheric pressure anion mass spectrometry: electron affinities and activation energies of thermal electron attachment - perfluoromethylcyclohexane, C7F14

RATIONALE

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.

Hylleraas hydride binding energy: diatomic electron affinities

Theoretical adiabatic electron affinities are often considered inaccurate because they are referenced to only a single value. Ground state electron affinities for all the main group elements and homonuclear diatomics were identified recently using the normalized binding energy of the hydrogen atom: [0.75420375(3)/2 = 0.37710187(1) eV]. Here we revisit experimental values and extend the identifications to diatomics in the G2-1 set. We assign new ground state electron affinities: (eV) Cl2, 3.2(2); Br2, 2.87(14); CH, 2.1(2); H2, 0.6 ; NH, 1.1, SiH, 1.90. Anion Morse potentials are calculated for H2 and N2 from positive electron affinities and for hyperfine superoxide states for the first time.