Steric Effects in Electron Transfer from Potassium to -Bonded Oriented Molecules CH

Electron transfer from K atoms to oriented CH3CN, CH3NC, and CCl3CN is studied in crossed beams at energies near the threshold for forming an ion pair. For the methyl compounds, the dominant ions are K+ and CN-; the steric asymmetry is very small and energy-independent, characteristic of sideways attack with the electron apparently entering the π*CN antibonding orbital. Migration of the electron to the σ*CC orbital to break the C-C bond is greatly facilitated by interaction with the atomic donor. CH2CN is formed in collisions preferring CH3-end attack, and the steric asymmetry becomes very large near threshold. CCl3CN mostly forms Clin collisions slightly favoring the CCl3 end with a small energy dependence with the electron apparently entering the σ* LUMO. CNis formed in much smaller yield with a slight preference for the CN end. The parent negative ion CCl3CN is observed, and a lower limit for its electron affinity is estimated to be 0.3 eV. Fragment ions CCl2CN and CClCNare also observed with upper limits for the quantity bond dissociation energy electron affinity (BDE EA) estimated to be 0.6 and 1.0 eV, respectively.