Electron affinities and activation energies for reactions with thermal electrons:: SF6 and SF5

Negative ion mass spectrometry and pulsed discharge electron capture detector data for thermal electron attachment to SF6 are reported. Electron affinities and activation energies for SF6 and SF5 are obtained from these data and literature magnetron, swarm, beam, and collisional ionization data. The thermodynamic and kinetic data cover temperatures from 50 to 7500 K. The largest electron affinity of SF6, 2.60(10) eV is assigned to the adiabatic electron affinity. The numbers in parentheses indicate uncertainties. Excited state values are (in eV) 2.45(3), 2.20(3), 2.00(3), 1.80(3), 1.60(3), 1.20(3), 1.04(3), 0.80(3), 0.65(3), 0.45(3), 0.35(3), 0.25(3), and 0.10(10). The activation energies range from near zero to 0.65(2) eV. The adiabatic electron affinity of SF5, 3.85(2) eV and an excited state value, 2.77(5) eV are obtained from a kinetic analysis of published magnetron data. The energies for dissociative electron attachment to give SF5(-), F(-), and excited state SF5(-) are 0.20(11) eV, 0.65(10) eV, and 1.28(11) eV from the SF5-F dissociation energy, the electron affinity of the fluorine atom, and these values. The average relative anion bond orders for the bonding curves is 0.63(2) and for the antibonding curves is 0.30(2). Fourteen Herschbach ionic Morse Person empirical curves are calculated from these data. Six bonding and six antibonding curves are pseudo-two-dimensional cuts through the multidimensional surface. Representative long-range anionic curves are calculated in reaction coordinates analogous to Marcus parabolas.