  Frontiers of attosecond science are constantly shifting, thus addressing more
and more intricate effects with increasing resolution. Ultrashort pulses offer
a practical way to prepare complex superpositions of quantum states, follow,
and steer their dynamics. In this contribution, an ultrafast spin-flip process
triggered by sub-femtosecond (fs) excitation and strong spin-orbit coupling
between 2p core-excited states of a transition metal complex is investigated
using density matrix-based time-dependent restricted active space configuration
interaction theory. The effect of the nuclear vibrations is incorporated making
use of an electronic system plus vibrational bath partitioning. The differences
between isolated sub-fs pulses and pulse trains as well as influence of various
pulse characteristics on the initiated dynamics are discussed. The effect under
study can be potentially used for ultrafast clocking in sub-few fs experiments.
