Femtosecond time-resolved surface reaction: Desorption of Co from Cu(111) in <325 fsec

Abstract

The laser-induced desorption of CO molecules from a Cu(111) surface is time resolved with 100-fsec resolution. We find the desorption reaction is completed in \ensuremath{\le}325 fsec after the 100-fsec, 2-eV photon energy pump pulse. The only mechanism consistent with this abrupt, efficient (\ensuremath{\sigma}\ensuremath{\sim}${10}^{18}$ ${\mathrm{cm}}^{2}$) desorption is a novel one: The transient hot substrate electrons (${\mathit{T}}_{\mathrm{e}\mathrm{l}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{n},\mathrm{m}\mathrm{a}\mathrm{x}}$\ensuremath{\sim}3600 K, while ${\mathit{T}}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{e},\mathrm{m}\mathrm{a}\mathrm{x}}$\ensuremath{\sim}160 K) drive ImultipleP electronic excitation-deexcitation cycles of the CO-Cu complex within the vibrational relaxation time. This vibrationally pumps the molecules into desorbing.