Abstract
Over the last four decades an experimental method has been developed that looks at molecular orbitals in
momentum space. The method, called electron momentum spectroscopy (EMS), is based on electroninduced
Compton scattering at incident electron energies of the order of 1 keV or higher. This account
reviews the most advanced form of EMS, which is called time-resolved EMS (TR-EMS) and employs
ultrashort laser and electron pulses in a pump/probe scheme. To illustrate the current status of TR-EMS,
we present an experiment on the three-body photodissociation dynamics of the deuterated acetone
molecule at 195 nm. Although there is ample room for improvement such as in data statistics, our
experiment demonstrates that molecular orbital imaging of short-lived transient species is feasible,
opening the door to exploiting a new area of studies on ultrafast molecular dynamics as well as the
nature of molecular excited states.
