Carbon $1s$ photoelectron spectra of methane are measured over a photon energy range between 480 eV and 1200 eV. Additional components appear between the individual symmetric stretching vibrational components and are attributed to the excitations of asymmetric stretching and bending vibrations due to recoil of the high-energy photoelectron emission. This recoil effect is the evidence for the violation of the Franck-Condon principle which states that neither the positions nor the momenta of the nuclei change during the ionization event.

Interatomic Coulombic decay (ICD) from an Auger-final dicationic state is observed in the Ar dimer. A $2p$ inner-shell vacancy created by photoionization is replaced with $3s$ and $3p$ vacancies via intra-atomic Auger decay. The Auger-final dicationic state is subject to ICD in which one of the $3p$ electrons in the same Ar atom fills the $3s$ vacancy while one of the $3p$ electrons from the neighboring Ar atom is emitted as an ICD electron. This ICD process is unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ICD electron and the kinetic energy release between ${\mathrm{Ar}}^{+}$ and ${\mathrm{Ar}}^{2+}$ are measured in coincidence.

We have measured two-dimensional photoelectron momentum spectra of Ne, Ar, and Xe generated by 800-nm, 100-fs laser pulses and succeeded in identifying the spectral ridge region (back-rescattered ridges) which marks the location of the returning electrons that have been backscattered at their maximum kinetic energies. We demonstrate that the structural information, in particular the differential elastic scattering cross sections of the target ion by free electrons, can be accurately extracted from the intensity distributions of photoelectrons on the ridges, thus effecting a first step toward laser-induced self-imaging of the target, with unprecedented spatial and temporal resolutions.

When an electron from a diatomic molecule undergoes tunneling-rescattering ionization, a novel form of destructive interference can be realized that involves all four geometric orbits that are available to the electron when it is freed, because both ionization and rescattering may take place at the same or at different centers. We find experimentally and confirm theoretically that in orientation-averaged angle-resolved high-order above-threshold ionization spectra the corresponding destructive interference is visible for ${\mathrm{O}}_2$ but not for ${\mathrm{N}}_2$. This effect is different from the suppression of ionization that is well known to occur for ${\mathrm{O}}_2$.