Illuminating molecules from within

Marc Vrakking
2009 Physics  
We present a numerical study of the ultrafast ionization dynamics of H 2 + exposed to attosecond extreme ultraviolet ͑xuv͒ pulses that goes beyond the Born-Openheimer approximation. The four-dimensional, timedependent Schrödinger equation was solved using a generalization of the finite-element discrete-variablerepresentation/real-space-product technique used in our previous calculations to include the dynamical motion of the nuclei. This has enabled us to expose the target to any polarized
more » ... any polarized light at arbitrary angles with respect to the molecular axis. Calculations have been performed at different angles and photon energies ͑ប =50 eV up to 630 eV͒ to investigate the energy and orientation dependence of the photoionization probability. A strong orientation dependence of the photoionization probability of H 2 + was found at a photon energy of ប = 50 eV. At this energy, we found that the ionization probability is three times larger in the perpendicular polarization than in the parallel case. These observations are explained by the different geometric "cross sections" seen by the photoejected electron as it leaves the molecule. This ionization anisotropy vanishes at the higher-photon energy of ប Ն 170 eV. When these higher-energy xuv pulses are polarized perpendicular to the internuclear axis, a "double-slit-like" interference pattern is observed. However, we find that the diffraction angle only approaches the classical formula n = sin −1 ͑n e / R 0 ͒, where n is the diffraction order, e is the released electron wavelength, and R 0 is the internuclear distance, when n e becomes less than 65% of R 0 . These results illustrate the possibility of employing attosecond pulses to perform photoelectron microscopy of molecules.
doi:10.1103/physics.2.72 fatcat:gkpd7hp2tfg5pho2ccc2gcxm3e