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 thezeroth 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 aresonance 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 invariablyautodetach after some time.
† Aquantum offset of the velocity imaging-based measurements was revealed in 2025,[3] which could make a revision of all electron affinities marked with a dagger† necessary. The value of the downward correction to be applied is determined by the intensity of the electric field that was used in the experiment, which was not published with the original measurements, but can be estimated to be of the order of −20 μeV.
The electron affinitiesEea of some molecules are given in the table below, from the lightest to the heaviest. Many more have been listed byRienstra-Kiracofe et al. (2002). The electron affinities of theradicals 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,PMID11782134.
Updated values can be found in theNIST chemistry webbook for around three dozen elements and close to 400 compounds.
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,Bibcode:1988JChTh..20..523B,doi:10.1016/0021-9614(88)90080-8
Chaibi, W.; Delsart, C.; Drag, C.; Blondel, C. (2006), "High precision measurement of the32SH 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,Bibcode:1986JAChS.108.5453C,doi:10.1021/ja00278a014
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,PMID15638660
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,PMID24929396,S2CID1061364
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
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. (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
^Beyer M. & Merkt F. (2018). "Communication: Heavy-Rydberg states of HD and the electron affinity of the deuterium atom".J. Chem. Phys.149, 031102doi:10.1063/1.5043186
^abcdefghijklmBratsch, S.G.; Lagowski, J.J. (1986). "Predicted stabilities of monatomic anions in water and liquid ammonia at 298.15 K.".Polyhedron.5 (11):1763–1770.doi:10.1016/S0277-5387(00)84854-8.
^abBlondel, C.; Delsart, C.; Valli, C.; Yiou, S.; Godefroid, M.R.; Van Eck, S. (2001). "Electron affinities of16 O,17 O,18 O, the fine structure of16O−, and the hyperfine structure of17O−".Phys. Rev. A.64 (5) 052504.Bibcode:2001PhRvA..64e2504B.doi:10.1103/PhysRevA.64.052504.
^abBlondel, C.; Cacciani, P.; Delsart, C.; Trainham, R. (1989). "High Resolution Determination of the Electron Affinity of Fluorine and Bromine using Crossed Ion and Laser Beams".Phys. Rev. A.40 (7):3698–3701.Bibcode:1989PhRvA..40.3698B.doi:10.1103/PhysRevA.40.3698.PMID9902584.
^Scheer, M.; Bilodeau, R.C.; Thøgersen, J.; Haugen, H.K. (1998). "Threshold Photodetachment of Al−: Electron Affinity and Fine Structure".Phys. Rev. A.57 (3): R1493–96.Bibcode:1998PhRvA..57.1493S.doi:10.1103/PhysRevA.57.R1493.
^Fu, X.; Luo, Z.; Chen, X.; Li, J.; Ning, C. (2016). "Accurate electron affinity of V and fine-structure splittings of V− via slow-electron velocity-map imaging".J. Chem. Phys.145 (16): 164307.Bibcode:2016JChPh.145p4307F.doi:10.1063/1.4965928.PMID27802620.
^Chen, X.; Ning, C. (2016). "Accurate electron affinity of Co and fine-structure splittings of Co− via slow-electron velocity-map imaging".Phys. Rev. A.93 (5) 052508.Bibcode:2016PhRvA..93e2508C.doi:10.1103/PhysRevA.93.052508.
^abcScheer, M.; Brodie, C.A.; Bilodeau, R.C.; Haugen, H.K. (1998). "Laser spectroscopic measurements of binding energies and fine-structure splittings of Co−, Ni−, Rh−, and Pd−".Phys. Rev. A.58 (3):2051–62.Bibcode:1998PhRvA..58.2051S.doi:10.1103/PhysRevA.58.2051.
^Frey, P.; Breyer, F.; Hotop, H. (1978). "High Resolution Photodetachment from the Rubidium Negative Ion around the Rb(5p1/2) Threshold. Journal of Physics BJ. Phys. B: At. Mol. Phys".Chinese Journal of Chemical Physics.11: L589–94.doi:10.1088/0022-3700/11/19/005.
^Andersen, H.H.; Petrunin, V.V.; Kristensen, P.; Andersen, T. (1997). "Structural properties of the negative strontium ion: Binding energy and fine-structure splitting".Phys. Rev. A.55 (4):3247–49.Bibcode:1997PhRvA..55.3247A.doi:10.1103/PhysRevA.55.3247.
^Fu, X.; Li, J.; Luo, Z.; Chen, X.; Ning, C. (2017). "Precision measurement of electron affinity of Zr and fine structures of its negative ions. Journal of Chemical Physics J. Chem. Phys".The Journal of Chemical Physics.147 (6): 064306.doi:10.1063/1.4986547.PMID28810756.
^Luo Z., Chen X., Li J. & Ning C. (2016). Precision measurement of the electron affinity of niobium.Phys. Rev. A93, 020501(R)doi:10.1103/PhysRevA.93.020501
^abcdefCRC Handbook of Chemistry and Physics 92nd Edn. (2011–2012); W. M. Haynes. Boca Raton, FL: CRC Press. "Section 10, Atomic, Molecular, and Optical Physics; Electron Affinities".
^Walter, C.W.; Gibson, N.D.; Carman, D.J.; Li, Y.-G.; Matyas, D.J. (2010). "Electron affinity of indium and the fine structure of In− measured using infrared photodetachment threshold spectroscopy".Phys. Rev. A.82 (3) 032507.Bibcode:2010PhRvA..82c2507W.doi:10.1103/PhysRevA.82.032507.
^Nadeau, M. J.; Garwan, M. A.; Zhao, X. L.; Litherland, A. E. (1997). "A negative ion survey; towards the completion of the periodic table of the negative ions".Nuclear Instruments and Methods in Physics Research B.123 (1–4):521–526.Bibcode:1997NIMPB.123..521N.doi:10.1016/S0168-583X(96)00749-5.
^Tang R., Chen X., Fu X., Wang H. and Ning C. (2018). Electron affinity of the hafnium atom.Phys. Rev. A98 020501(R)doi:10.1103/PhysRevA.98.020501.
^Chen, X.L.; Ning, C.G. (2017). "Observation of Rhenium Anion and Electron Affinity of Re".J. Phys. Chem. Lett.8 (12):2735–2738.doi:10.1021/acs.jpclett.7b01079.PMID28581753.
^Lu Y., Zhao J., Tang R., Fu X. & Ning C. (2020). "Measurement of electron affinity ofiridium atom and photoelectron angular distributions of iridium anion".J. Chem. Phys.152, 034302doi:10.1063/1.5134535
^Bilodeau, R.C.; Scheer, M.; Haugen, H.K.; Brooks, R.L. (1999). "Near-threshold Laser Spectroscopy of Iridium and Platinum Negative Ions: Electron Affinities and the Threshold Law".Phys. Rev. A.61 (1) 012505.Bibcode:1999PhRvA..61a2505B.doi:10.1103/PhysRevA.61.012505.
^Junqin, Li; Zilong, Zhao; Martin, Andersson; Xuemei, Zhang; Chongyang, Chen (2012). "Theoretical study for the electron affinities of negative ions with the MCDHF method".J. Phys. B: At. Mol. Opt. Phys.45 (16) 165004.Bibcode:2012JPhB...45p5004L.doi:10.1088/0953-4075/45/16/165004.S2CID121023909.
^abLandau, A.; Eliav, E.; Ishikawa, Y.; Kaldor, U. (2001). "Benchmark calculations of electron affinities of the alkali atoms sodium to eka-francium (element 119)".J. Chem. Phys.115 (6): 2389.Bibcode:2001JChPh.115.2389L.doi:10.1063/1.1386413.
^Tang R., Si R., Fei Z., Fu X., Lu Y., Brage T., Liu H., Chen C. & Ning C. (2019). "Candidate for Laser Cooling of a Negative Ion:High-Resolution Photoelectron Imaging of Th−".Phys. Rev. Lett.123, 203002doi:10.1103/PhysRevLett.123.203002
^abcdefghijklGuo, Y.; Whitehead, M.A. (1989). "Electron affinities of alkaline-earth element calculated with the local-spin-density-functional theory".Physical Review A.40 (1):28–34.doi:10.1103/PhysRevA.40.28.PMID9901864.
^Tang R., Lu Y., Liu H. & Ning C. (2021). "Electron affinity of uranium and bound states of opposite parity in its anion".Phys. Rev. A103, L050801doi:10.1103/PhysRevA.103.L050801
^Guo, Yangyang; Pašteka, Lukáš F.; Eliav, Ephraim; Borschevsky, Anastasia (2021). "Chapter 5: Ionization potentials and electron affinity of oganesson with relativistic coupled cluster method". In Musiał, Monika; Hoggan, Philip E. (eds.).Advances in Quantum Chemistry. Vol. 83. pp. 107–123.ISBN978-0-12-823546-1.
^Borschevsky, A.; Pershina, V.; Eliav, E.; Kaldor, U. (2013). "Ab initio predictions of atomic properties of element 120 and its lighter group-2 homologues".Phys. Rev. A.87 (2): 022502–1–8.Bibcode:2013PhRvA..87b2502B.doi:10.1103/PhysRevA.87.022502.
^Calculated on basis of the values for sulhydryl and the eV value of the cyano radical as the kJ/Mol value was missing from the list on march 18, 2025.
^Bradforth, Stephen E.; Kim, Eun Ha; Arnold, Don W.; Neumark, Daniel M. (1993-01-15). "Photoelectron spectroscopy of CN−, NCO−, and NCS−".The Journal of Chemical Physics.98 (2). AIP Publishing:800–810.doi:10.1063/1.464244.ISSN0021-9606.
^abcdefghiRayner-Canham Appendix 5: Data summarised from, and see also, J. E. Huheey et al., Inorganic Chemistry, 4th ed. (New York: HarperCollins, 1993)[1]
^According toNIST as concernsBoron trifluoride, the Magnetron method, lacking mass analysis, is not considered reliable.
