Knowledge Bank

Photoelectrons generated in the photoinonization of acetyiene are observed to produce G2H- upon collision with other $C2H2$ molecules. The photoelectron energy can be continously tuned from O- SeV by varying the incident photon energy from 11:40 eV (the ionization potential of $C2H2$) to higher energy. The dissociative attachement process $e+C2H2-C2H-+H$ has a threshold at $877\pm 2\backslash AA$ corresponding to a photoelectron energy of $2.74\pm 0.03eV$. The same threshold value has been obtained at $298\circ K$ and $-150\circ K$, and hence the temperature dependence, if any, is slight. When this threshold is combined with E.A. $(C2H2)=2.969\pm 0.010eV$, one obtains $D0(HC2-H)5.71\pm 0.03eV=131.6\pm 0.7Kcal/mol$.