Dynamical simulations of photochemical reactions of \textit{trans}-stilbene, and coherent control of C$_{60}$ vibrational response*

\textit{Trans}-to-\textit{cis} photoisomerization of stilbene, induced by a femtosecond-scale laser pulse, has been observed in simulations employing semiclassical electron-radiation-ion dynamics (SERID). Our results demonstrate that \textit{trans}-to-\textit{cis} and \textit{cis}-to-\textit{trans} isomerization involve the same basic mechanism. We also predict that another photochemical reaction, photocyclization of \textit{trans}-stilbene to 4a,4b-dihydrophenanthrene (DHP), can be achieved using an ultrashort laser pulse. Specifically, the trans-stilbene molecule is observed first to isomerize to cis-stilbene (as an excited-state intermediate) after more than one picosecond, and then to form a new bond to become DHP, after a few hundred additional femtoseconds. For C$_{60}$ at low temperature, we predict that specific vibrational modes can be excited by optimally choosing the delay between two femtosecond-scale pulses.