We have studied the relaxation dynamics of optically excited electrons in molybdenum and rhodium by means of time resolved two-photon photoemission spectroscopy (TR-2PPE) and ab initio electron self-energy calculations performed within the GW and GW + T approximations. Both theoretical approaches reproduce qualitatively the experimentally observed trends and differences in the lifetimes of excited electrons in molybdenum and rhodium. For excitation energies exceeding the Fermi energy by more than 1 eV, the GW + T theory yields lifetimes in quantitative agreement with the experimental results. As one of the relevant mechanisms causing different excited state lifetime in Mo and Rh we identify the occupation of the 4d bands. An increasing occupation of the 4d bands results in an efficient decrease of the lifetime even for rather small excitation energies of a few 100 meV.

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Time-resolved two-photon photoemission of the doping process of perylene-tetracarboxylicdianhydride ͑PTCDA͒ thin films with sodium gives insight into the dynamics of hot electrons in this system. Interaction with Na results in a charge transfer from Na to PTCDA and increases the lifetime of optically excited electrons. A similar increase in lifetime can be observed for ultrathin PTCDA layers on Ag͑111͒. Both results are discussed in the one-electron picture, treated in "classical" photoemission theory, and in the many-electron picture as commonly considered for strongly correlated systems.