Long-lived parent negative ions formed via nuclear-excited Feshbach resonances. Part 3.—Variation of the autodetachment lifetime with incident electron energy

Abstract

The autodetachment lifetimes of the long-lived parent negative ions of o-nitrophenol (o-C₆H₄-OHNO₂), benzil (C₆H₅COCOC₆H₅), and tetracyanoethylene (C₂(CN)₄)—formed via nuclear-excited Feshbach resonances—decrease with increasing incident electron energy. The lifetimes for o-C₆H₄OHNO^–* ₂, C₆H₅COCOC₆H^–* ₅, and C₂(CN)^–* ₄ decrease from 420, 85, and 55 µs at 0.0 eV to 90, 10, and 11 µs at 0.6, 1.5, and 0.8 eV, respectively. These lifetime variations are theoretically treated and are attributed to the increase in the probability of autodetachment with increasing electron energy (which increases the compound negative ion's internal energy) due to the increase in the number of final neutral-molecule states to which the unstable compound negative ion can decay. From the theoretical analysis presented, the autodetachment lifetime is found to decrease with increasing incident electron energy much faster than is experimentally measured.