Mass Spectrometric determination of the Electronaffinities of Radicals.

By mass spectrometric study of the appearance of C2-, CH- and C2H- from CH4, C2H2, C2H4, C2H3X (X=F, Cl) the following electronaffinities have been determined: EA(CH)=(2.6+/-0.3) eV, EA(C2)=(3.3+/-0.2) eV and EA(C2H)=(2.1+/-0.3) eV. Some evidence is brought to the existence of electronic excited states of these ions. An evaluation of these negative ions dissociation energy in their ground electronic state is given and is found to be of the order of magnitude of the corresponding isoelectronic molecular species dissociation energy.