We use the time-dependent $R$-matrix approach to investigate an ultrashort pump-probe scheme to observe collective electron dynamics in ${\mathrm{C}}^{+}$. The ionization probability of a coherent superposition of the $2s2p^2{}^{2}D$ and ${}^{2}S$ states shows rapid modulation due to collective dynamics of the two equivalent $2p$ electrons, with the modulation frequency linked to the dielectronic repulsion. The best insight into this collective dynamics is achieved by a transformation from $LS$ symmetry to the uncoupled basis. Such dynamics may be important in high-harmonic generation using open-shell atoms and ions.

• Received 5 February 2009

DOI:https://doi.org/10.1103/PhysRevLett.102.193001