Dr. Arnaud Rouzée is the recipient of the 2020 "JCP Editor's Choice Award"
In this work that was done in collaboration with the group of Jochen Küpper from the Center for Free Electron Lasers (CFEL) in Hamburg, laser-induced electron diffraction (LIED) was used to determine the bond lengths of the carbonyl sulfide (OCS) molecule. In the experiment, an intense and ultrashort mid-infrared laser field was used to ionize OCS molecules and the angle-resolved photoelectron distribution was recorded using a newly developed velocity map imaging spectrometer designed to reach a maximum kinetic energy of 500 eV. In the strong laser field, an electron was removed from each molecule and accelerated away by the laser field before being driven back to its parent ion, inducing elastic scattering of the electron. The scattered electron was once more accelerated in the laser field, reaching a very high kinetic energy. By extracting the differential electron scattering cross section (DCS) of the molecule from the angular distribution of these high-energy electrons, Rouzée and co-workers were able to extract the molecular bond lengths of the OCS molecule to a precision better than 5 pm. The experiment was done using only 10 minutes of integration time, which is almost a 100-fold improvement with respect to previous studies. Thereby, the experiment opens a new path towards directly recording a so-called “molecular movie”, in which the evolving structure of a molecule during a photochemical reaction is measured with femtosecond and picometer resolution.
Photoelectron angular distribution recorded in OCS molecules ionized by a 2 μm laser field and used to retrieve the molecular bond lengths.