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 These data, unpublished radioactive and pulsed discharge ECD thermal data from the University of Houston laboratories are used to report and evaluate electron affinities.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.

Comment on: Negative ions, molecular electron affinity and orbital structure of cata-condensed polycyclic aromatic hydrocarbons by Rustem V. Khatymov, Mars V. Muftakhov and Pavel V. Shchukin.

RATIONALE: The anion mass spectral lifetimes for several aromatic hydrocarbons reported in the subject article were related to significantly different electron affinities. The different values are rationalized using negative ion mass spectral data. METHODS: Electron affinities for polycyclic aromatic hydrocarbons are reported from the temperature dependence of unpublished electron capture detector data. These are compared with published values and the largest values are assigned to the ground state. RESULTS: The ground state adiabatic electron affinities: (eV) pentacene, 1.41 (3); tetracene, 1.058 (5); benz(a)pyrene, 0.82 (4); benz(a) anthracene, 0.69 (2) anthracene, 0.68 (2); and pyrene, 0.59 (1) are used to assign excited state adiabatic electron affinities: (eV) tetracene: 0.88 (4); anthracene 0.53 (1); pyrene, 0.41 (1); benz(a)anthracene, 0.39 (10); chrysene, 0.32 (1); and phenanthrene, 0.12 (2) and ground state adiabatic electron affinities: (eV) dibenz(a,j)anthracene, 0.69 (3); dibenz(a,h)anthracene, 0.68 (3); benz(e)pyrene, 0.60 (3); and picene, 0.59 (3) from experimental data. The lifetime of benz(a)pyrene is predicted to be larger than 150 µs and for benzo(c)phenanthrene and picene about 40 µs, from ground state adiabatic electron affinities. CONCLUSIONS: The assignments of adiabatic electron affinities of aromatic hydrocarbons determined from electron capture detector and mass spectrometric data to ground and excited states are supported by constant electronegativities. A set of consistent ground state adiabatic electron affinities for 15 polycyclic aromatic hydrocarbons is related to lifetimes from the subject article.

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.

Negative surface ionization electron affinities and activation energies of SF(n).

RATIONALE: Sulfur hexafluoride (SF6 ) is the most frequently used standard for anion mass spectrometry because of its large temperature-independent cross-section for electron attachment. However, the kinetic and thermodynamic properties--the products of the reactions, and the number of negative ion states of the SF(n)--are presently in dispute. METHODS: The electron affinities for SF(n) (n = 1-6) are predicted by assuming dissociation energies and ground-state electron affinities based on literature values. The temperature dependence of the 2012 negative surface ionization mass spectrometer data, and other negative ionization mass spectrometry, electron capture detector, and beam and magnetron data, are analyzed using a kinetic model. RESULTS: More precise and accurate activation energies for thermal electron attachment and electron affinities of SF6 , SF5 and SF4 are reported. The largest experimental electron affinities of SF, SF2 and SF3 are assigned to the ground states. Ionic Morse potentials for multiple states are calculated. A mechanism for the formation of the ionic products observed in negative surface ionization thermal electron attachment to SF6 is presented. CONCLUSIONS: Negative surface ionization on a hot filament with mass spectrometry is a relatively simple and effective method for determining electron affinities similar to the electron capture detector, magnetron, swarm and beam procedures. A new method of predicting the number of negative ion states from dissociation limits establishes targets for the data analysis. Pseudo one-dimensional anionic Morse potentials illustrate the mechanism for the reaction of thermal electrons with SF6 and the consecutive dissociation pathways.

The electron affinities of deprotonated adenine, guanine, cytosine, uracil, and thymine.

Electron attachment rates and gas phase acidities for the canonical tautomers of the nucleobases and electron affinities for thymine, deprotonated thymine, and cytosine are reported The latter are from a new analysis of published photoelectron spectra. The values for deprotonated thymine are (all in eV) keto-N1-H, 3.327(5); enol-N3-H, 3.250(5), enol-C2OH, 3.120(5) enol-N1-H, 3.013(5), and enol-C4OH,3.123(5). The values for deprotonated cytosine, keto-N1-H, 3.184(5); trans-NH-H, 3.008(5); cis-NH-H, 3.039(5); and enol-N1-H, 2.750(5) and enol-O-H, 2.950(5). The gas phase acidities from these values are obtained from these values using experimental or theoretical calculations of bond dissociation energies. Kinetic and thermodynamic properties for thermal electron attachment to thymine are obtained from mass spectrometric data. We report an activation energy of 0.60 eV and electron affinity of thymine, 1.0(1) eV.

Electron attachment to C(2)Cl(4) and Trojan horse ionization.

In a recent study of tetrachloroethylene, the anion yield curves were analyzed using three published negative-ion Morse potentials. Unexpected ions at zero electron energy were explained by the "Trojan horse" mechanism. This communication also attributes formation of Cl(2)(-) at higher energies to a Trojan horse mechanism. Six new Morse potentials are calculated to account for the observed anion states. These combine all extant electron impact and attachment data. The electron affinity of the C(2)Cl(3) radical, 3.1(1) eV, and the C-Cl bond dissociation energy 4.0(1) eV are reported.

Electron-capture detector and multiple negative ions of aromatic hydrocarbons.

Multiple electron affinities are identified in the temperature dependence of the electron-capture detector: naphthalene, 0.16, 0.13+/-0.01, anthracene, 0.69, 0.60, 0 53+/-0.01; tetracene 1.1, 0.88+/-0.03, 0.53+/-0.05; pyrene, 0.61, 0.50+/-0.02; azulene 0.90, 0.80, 0.70+/-0.02, 0.65, 0.55+/-0.05; acenaphthylene, 0.80, 0.69, 0.60, 0.50+/-0.05; and c-C8H8, 0.80, 0.70, 0.55+/-0.02; (all in eV). These are obtained from a rigorous least squares procedure incorporating literature values and uncertainties. The adiabatic electron affinities for about 40 hydrocarbons listed in the US National Institute of Standards and Technology (NIST) tables are evaluated. The adiabatic electron affinity values not listed in NIST are biphenylene, 0.45+/-0.05 eV and coronene. 0.8+/-0.05 eV. Morse potential energy curves in the C-H dimensions illustrate multiple states for benzene and naphthalene.