Observation of ultrafast dynamics in CO2 highly excited states

A complete investigation of the ultrafast dynamics happening in highly excited molecular states represents a true challenge. On the theoretical side the mixed character and the delocalized nature of these excitations is rather demanding. Moreover, their experimental observation is not straightforward. As the lifetime of these states is usually very short (few hundreds to few tens of femtoseconds) their excitation requires few-femtosecond light pulses in the extreme-ultraviolet region (EUV) [1]. Here we used 10-fs EUV pulses at ~17 eV to populate the excited states of carbon dioxide below the first excited state of the molecular cation (Ã) corresponding to the HOMO-1 photoionization. Their population is subsequently probed by a 15-fs IR pulse centred around 800 nm (photon energy about 1.56 eV), revealing rich dynamics and oscillations with a period as fast as 24 fs, never observed before.