Positive- and negative-ion formation due to the electron bombardment of germanium tetrafluoride

Abstract

The formation of positive and negative ions resulting from the electron bombardment of germanium tetrafluoride has been studied as a function of electron energy. Appearance potentials have been measured for these ions and various ionisation processes suggested to explain their formation. From these data bond dissociation energies of several species have been deduced and trends noted for the fluorides of carbon, silicon and germanium are compared with those reported for the analogous hydrides. A parent negative ion is formed by germanium tetrafluoride as a result of the capture of zero-energy electrons, the electron attachment cross-section being estimated as 1.5 ± 0.3 × 10 −16 cm 2. At ion source pressures greater than ∼10 −5 torr, secondary negative ions such as GeF 5 −, Ge 2F 4 −, Ge 2F 8 − are observed to be formed as a result of ion-molecule reactions. GeF 5 − is formed by the reaction GeF 3 − + GeF 4 → GeF 5 − + GeF 2. A value of 2.9 × 10 −10 molec −1 cm 3 sec −1 has been estimated for the rate constant of the reaction.