Electron affinity (data page)

Electron affinity can be defined in two equivalent ways. First, as the energy that is released by adding an electron to an isolated gaseous atom. The second (reverse) definition is that electron affinity is the energy required to remove an electron from a singly charged gaseous negative ion. The latter can be regarded as the ionization energy of the –1 ion or the zeroth ionization energy.^[1] Either convention can be used.^[2]

Negative electron affinities can be used in those cases where electron capture requires energy, i.e. when capture can occur only if the impinging electron has a kinetic energy large enough to excite a resonance of the atom-plus-electron system. Conversely electron removal from the anion formed in this way releases energy, which is carried out by the freed electron as kinetic energy. Negative ions formed in these cases are always unstable. They may have lifetimes of the order of microseconds to milliseconds, and invariably autodetach after some time.

The electron affinities E_ea of some molecules are given in the table below, from the lightest to the heaviest. Many more have been listed by Rienstra-Kiracofe et al. (2002). The electron affinities of the radicals OH and SH are the most precisely known of all molecular electron affinities.

• Janousek, Bruce K.; Brauman, John I. (1979), "Electron affinities", in Bowers, M. T. (ed.), Gas Phase Ion Chemistry, vol. 2, New York: Academic Press, p. 53.
• Rienstra-Kiracofe, J.C.; Tschumper, G.S.; Schaefer, H.F.; Nandi, S.; Ellison, G.B. (2002), "Atomic and molecular electron affinities: Photoelectron experiments and theoretical computations", Chem. Rev., vol. 102, no. 1, pp. 231–282, doi:10.1021/cr990044u, PMID 11782134.
• Updated values can be found in the NIST chemistry webbook for around three dozen elements and close to 400 compounds.

Specific molecules

• Adams, C.L.; Schneider, H.; Ervin, K.M.; Weber, J.M. (2009), "Low-energy photoelectron imaging spectroscopy of nitromethane anions: Electron affinity, vibrational features, anisotropies, and the dipole-bound state", J. Chem. Phys., 130 (7): 074307, Bibcode:2009JChPh.130g4307A, doi:10.1063/1.3076892, PMID 19239294
• Borshchevskii, A.Ya.; Boltalina, O.V.; Sorokin, I.D.; Sidorov, L.N. (1988), "Thermochemical quantities for gas-phase iron, uranium, and molybdenum fluorides, and their negative ions", J. Chem. Thermodyn., 20 (5): 523, doi:10.1016/0021-9614(88)90080-8
• Chaibi, W.; Delsart, C.; Drag, C.; Blondel, C. (2006), "High precision measurement of the ³²SH electron affinity by laser detachment microscopy", J. Mol. Spectrosc., 239 (1): 11, Bibcode:2006JMoSp.239...11C, doi:10.1016/j.jms.2006.05.012
• Chowdhury, S.; Kebarle, P. (1986), "Electron affinities of di- and tetracyanoethylene and cyanobenzenes based on measurements of gas-phase electron-transfer equilibria", J. Am. Chem. Soc., 108 (18): 5453, doi:10.1021/ja00278a014
• Ervin, K.M.; Ho, J.; Lineberger, W.C. (1988), "Ultraviolet photoelectron spectrum of nitrite anion", J. Phys. Chem., 92 (19): 5405, doi:10.1021/j100330a017
• Ervin, K.M.; Lineberger, W.C. (1991), "Photoelectron spectra of C⁻
  ₂ and C₂H⁻", J. Phys. Chem., 95 (3): 1167, doi:10.1021/j100156a026
• George, P.M.; Beauchamp, J.L. (1979), "The electron and fluoride affinities of tungsten hexafluoride by ion cyclotron resonance spectroscopy", Chem. Phys., 36 (3): 345, Bibcode:1979CP.....36..345G, doi:10.1016/0301-0104(79)85018-1
• Goldfarb, F.; Drag, C.; Chaibi, W.; Kröger, S.; Blondel, C.; Delsart, C. (2005), "Photodetachment microscopy of the P, Q, and R branches of the OH⁻(v=0) to OH(v=0) detachment threshold", J. Chem. Phys., 122 (1): 014308, Bibcode:2005JChPh.122a4308G, doi:10.1063/1.1824904, PMID 15638660
• Huang, Dao-Ling; Dau, Phuong Diem; Liu, Hong-Tao; Wang, Lai-Sheng (2014), "High-resolution photoelectron imaging of cold C⁻
  ₆₀ anions and accurate determination of the electron affinity of C₆₀", J. Chem. Phys., 140 (22): 224315, Bibcode:2014JChPh.140v4315H, doi:10.1063/1.4881421, PMID 24929396, S2CID 1061364
• Kim, J.B.; Weichman, M.L.; Neumark, D.M. (2015), "Low-lying states of FeO and FeO⁻ by slow photoelectron spectroscopy", Mol. Phys., 113 (15–16): 2105, Bibcode:2015MolPh.113.2105K, doi:10.1080/00268976.2015.1005706, S2CID 13868986
• Mathur, B.P.; Rothe, E.W.; Tang, S.Y.; Reck, G.P. (1976), "Negative ions from phosphorus halides due to cesium charge exchange", J. Chem. Phys., 65 (2): 565, Bibcode:1976JChPh..65..565M, doi:10.1063/1.433109
• Mead, R.D.; Lykke, K.R.; Lineberger, W.C.; Marks, J.; Brauman, J.I. (1984), "Spectroscopy and dynamics of the dipole-bound state of acetaldehyde enolate", J. Chem. Phys., 81 (11): 4883, Bibcode:1984JChPh..81.4883M, doi:10.1063/1.447515
• Miller, T.M.; Leopold, D.G.; Murray, K.K.; Lineberger, W.C. (1986), "Electron affinities of the alkali halides and the structure of their negative ions", J. Chem. Phys., 85 (5): 2368, Bibcode:1986JChPh..85.2368M, doi:10.1063/1.451091
• Nimlos, Mark R.; Ellison, G. Barney (1986), "Photoelectron spectroscopy of sulfur-containing anions (SO⁻
  ₂, S⁻
  ₃, and S₂O⁻)", J. Phys. Chem., 90 (12): 2574, doi:10.1021/j100403a007
• Novick, S.E.; Engelking, P.C.; Jones, P.L.; Futrell, J.H.; Lineberger, W.C. (1979), "Laser photoelectron, photodetachment, and photodestruction spectra of O⁻
  ₃", J. Chem. Phys., 70 (6): 2652, Bibcode:1979JChPh..70.2652N, doi:10.1063/1.437842
• Page, F. M.; Goode, G. C. (1969), Negative ions and the magnetron, John Wiley & Sons^[75]
• Ruoff, R.S.; Kadish, K.M.; Boulas, P.; Chen, E.C.M. (1995), "Relationship between the Electron Affinities and Half-Wave Reduction Potentials of Fullerenes, Aromatic Hydrocarbons, and Metal Complexes", J. Phys. Chem., 99 (21): 8843, doi:10.1021/j100021a060
• Schiedt, J.; Weinkauf, R. (1995), "Spin-orbit coupling in the O⁻
  ₂ anion", Z. Naturforsch. A, 50 (11): 1041, Bibcode:1995ZNatA..50.1041S, doi:10.1515/zna-1995-1110, S2CID 197275321
• Schiedt, J.; Weinkauf, R. (1999), "Resonant photodetachment via shape and Feshbach resonances: p-benzoquinone anions as a model system", J. Chem. Phys., 110 (1): 304, Bibcode:1999JChPh.110..304S, doi:10.1063/1.478066
• Schulz, P.A.; Mead, R.D.; Jones, P.L.; Lineberger, W.C. (1982), "OH⁻ and OD⁻ threshold photodetachment", J. Chem. Phys., 77 (3): 1153, Bibcode:1982JChPh..77.1153S, doi:10.1063/1.443980
• Sheps, L.; Miller, E.M.; Lineberger, W.C. (2009), "Photoelectron spectroscopy of small IBr⁻(CO₂)_n(n=0–3) cluster anions", J. Chem. Phys., 131 (6): 064304, Bibcode:2009JChPh.131f4304S, doi:10.1063/1.3200941, PMID 19691385
• Travers, M.J.; Cowles, D.C.; Ellison, G.B. (1989), "Reinvestigation of the electron affinities of O₂ and NO", Chem. Phys. Lett., 164 (5): 449, Bibcode:1989CPL...164..449T, doi:10.1016/0009-2614(89)85237-6
• Troe, J.; Miller, T.M.; Viggiano, A.A. (2012), "Communication:Revised electron affinity of SF₆ from kinetic data", J. Chem. Phys., 136 (2): 121102, Bibcode:2012JChPh.136l1102T, doi:10.1063/1.3698170, hdl:11858/00-001M-0000-000F-A0CD-D, PMID 22462826
• Wenthold, P.G.; Kim, J.B.; Jonas, K.-L.; Lineberger, W.C. (1997), "An Experimental and Computational Study of the Electron Affinity of Boron Oxide", J. Phys. Chem. A, 101 (24): 4472, Bibcode:1997JPCA..101.4472W, CiteSeerX 10.1.1.497.1352, doi:10.1021/jp970645u
• Zanni, M.T.; Taylor, T.R.; Greenblatt, B.J.; Soep, B.; Neumark, D.M. (1997), "Characterization of the I⁻
  ₂ anion ground state using conventional and femtosecond photoelectron spectroscopy", J. Chem. Phys., 107 (19): 7613, Bibcode:1997JChPh.107.7613Z, doi:10.1063/1.475110