1 Introduction The electron affinity (EA) of a species x has been defined in chemieal language as the exothermicity of the reaction x+e→x~+ at 298k; alternatively, in physical terms as the ionization potential of x~- or the difference in potential energy between x~- and the system x+e at infinite separation. The physical definition refers to an individual particle in isolation, i.e. to a temperature 1 Introduction The electron affinity (EA) of a species x has been defined in the chemieal language as the exothermicity of the reaction x + e → x ~ + at 298 k; alternatively, in physical terms as the ionization potential of x ~ - or the difference in potential energy between x ~ - and the system x + e at infinite separation. The physical definition refers to an individual particle in isolation, ie to a temperature