Nuclear and electronic dynamics in a wavepacket comprising bound Rydberg and valence electronic states of nitrogen from 12 to 15 eV are investigated using attosecond transient absorption. Vibrational quantum beats with a fundamental period of 50 femtoseconds persist for a picosecond in the b′ 1Σ+u valence state. Multi-state calculations show that these coherences result primarily from near infrared-induced coupling between the inner and outer regions of the b′ 1Σ+u state potential and the dark a″ 1Σ+g state. The excellent spectral and temporal resolution of this technique allows measurement of the anharmonicity of the b′ 1Σ+u potential directly from the observed quantum beats.

Excitation of ionic solids with extreme ultraviolet pulses creates localized core-level excitons, which in some cases couple strongly to the lattice. Here, core-level-exciton states of magnesium oxide are studied in the time domain at the Mg L_{2,3} edge with attosecond transient reflectivity spectroscopy. Attosecond pulses trigger the excitation of these short-lived quasiparticles, whose decay is perturbed by time-delayed near-infrared pulses. Combined with a few-state theoretical model, this reveals that the infrared pulse shifts the energy of bright (dipole-allowed) core-level-exciton states as well as induces features arising from dark core-level excitons. We report coherence lifetimes for the two lowest core-level excitons of 2.3±0.2 and 1.6±0.5  fs and show that these are primarily a consequence of strong exciton-phonon coupling, disclosing the drastic influence of structural effects in this ultrafast relaxation process.