CROSS-SECTION MEASUREMENTS FOR ELECTRON-IMPACT DISSOCIATION OF C4F8 INTO NEUTRAL AND IONIC RADICALS

The absolute cross sections for electron-impact dissociation of octafl uoro-cyclobutane (C4F8) into the neutral radicals CF, CF2, CF3 and C3F 5 are measured from the threshold to 250 eV. This measurement was acco mplished by appearance mass spectrometry in a dual electron beam devic e. The threshold energies for the neutral dissociation into CF, CF2 an d CF3 are 14.5, 10.5 and 12.8 eV, respectively, The cross sections for dissociation from C4F8 into CF2 and CF are much larger than those fro m CF4. Besides the neutral dissociation, the cross sections for the di ssociative ionization of C4F8 are extensively measured for formation o f CF+, CF2+, CF3+, C2F3+, C2F4+ and C3F5+.