Electron-molecule and electron-molecular ion collisions play an important role in the photophysics and photochemistry of planetary atmospheres and in plasmas. In laser-induced electron diffraction (LIED), we take benefit from the elastic rescattering of the returning electron in order to measure the corresponding differential cross sections. The specificity of the laser excitation allows us to work with aligned molecules using impulsive alignment, and to detect backscattering events, the detection of which is more challenging using electron beams. Femtosecond laser pulses at 0.8 µm in the 1014 Wcm-2 intensity range give access to scattering differential cross sections in the 1530 eV range in aligned molecules. The figure shows relative differential cross sections for CO2 molecules parallel to the laser polarization (top) and perpendicular to the laser polarization (bottom). On-going efforts are targeted at absolute values from the knowledge of the rescattering electron flux. The dynamics of rescattering is approached theoretically using the time-dependent Schrödinger equation (TDSE) and more recently the time-dependent density functional theory (TDDFT). Our goal is to compare our experimental electron spectra with calculated ones for a better understanding of electron collisions in aligned molecules.
Collaborations: ISMO (Université Paris-Saclay), LSI (École polytechnique)