ON THE COLLISIONAL DETACHMENT OF 2 ELECTRONS FROM C-4(-)

Double ionization of C-4(-) anions has been studied in collisions with Ar at an impact energy of 30 keV. Both non-dissociative and dissociat ive double detachment occur. The dominant channel leads to formation o f C+ + C-3 fragments. Branching ratios are investigated as a function of the voltage on the cathode of the Cs vapour sputter source of anion s; results indicate that C-4(-) anions are overwhelmingly produced in the ground electronic state over a wide range of operating conditions of such a source. Consideration of the energetics leads us to postulat e that the vertical ionization energy (IE) of C-3 is higher than the I E of C; a lower limit of 11.3 eV is placed for IE(C-3). (C) 1997 Elsev ier Science B.V.