This page deals with the electron affinity as a property of isolated atoms or molecules (i.e. in the gas phase).
First, as the energy that is released by adding an electron to an isolated gaseous atom.
† A quantum 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 affinities Eea of some molecules are given in the table below, from the lightest to the heaviest.