Visualizing coherent vibrational motion in the molecular iodine B 3Pi0+u state using ultrafast XUV transient absorption spectroscopy

Attosecond probing of core-level electronic transitions in molecules provides a sensitive tool for real-time
observation of chemical dynamics. Here, we employ ultrafast extreme-ultraviolet (XUV) transient
absorption spectroscopy to investigate the excited state electronic and nuclear dynamics in a prototype
molecule, I2. A few-femtosecond visible pump pulse is employed to excite the I2 molecule and an attosecond
XUV pulse is used to probe the dynamics through iodine-4d core-to-valence transitions. A highly extended
vibrational wave packet (v'=10-60, v'max=25) is prepared by one-photon absorption in the valence excited
B 3Pi_0+u state of I_2 and its motion is directly mapped due to the strong shift of the XUV core-level transition
with internuclear separation. Through the imaging of this vibrational motion, we directly reconstruct the
transition energy between the valence and the core-excited states as a function of internuclear distance.
Besides single-photon dynamics, distinct direct dissociation pathways arising from two-photon pump
absorption are also revealed.