The temperature dependences of the formation of negative ions from C6F6-xClx, CF3C6F5-xClx, and NC5F5-xClx (x = 1,2) were studied using negative chemical ionization mass spectrometry. Cl- and the parent negative ion were produced. The (M - Cl)(-) (M: parent molecule) was also observed for CF3C6F5-xClx and NC5F5-xClx. The temperature dependence of the relative intensity, (M - Cl)(-)/Cl-, suggested that the electron affinity of the fragment radicals decreases in the order, CF3C6F4 > C5F4N > C6F5. On the other hand, the relative intensity, Cl-/M-, suggested that the electron affinity of the parent molecules decreases in the order, CF3C6F5-xClx much greater than NC5F5-xClx > C6F6-xClx. Geometries of the parent anions were also calculated using with B3LYP/6-31+G method. The parent anions have an out-of-plane deformed structure and the extent of the deformation corresponds to that of the electron affinity for the parent molecule. (C) 2004 Elsevier B.V. All rights reserved.