ENHANCED FORMATION OF NEGATIVE-IONS BY ELECTRON-ATTACHMENT TO HIGHLY EXCITED MOLECULES IN A FLOWING AFTERGLOW PLASMA

Preliminary evidence for efficient negative-ion formation using a plas ma mixing scheme was reported in a recent letter [L. A. Pinnaduwage, W . Ding, and D. L. McCorkle, Appl. Phys. Lett. 71, 3634 (1997)]. In the present article we confirm the negative ion formation using a probe-a ssisted photodetachment technique and estimate rate constants for elec tron attachment to electronically excited CH4 and NO in a flowing afte rglow plasma. It is shown that enhanced electron attachment to molecul es in highly excited states populated via excitation transfer from rar e gas metastables is responsible for the observed negative ion formati on. Implications for plasma processing and plasma remediation discharg es are also discussed. (C) 1998 American Institute of Physics.