Directly imaging excited states-resolved coherent nuclear motions of water with picometer-femtosecond precision

Abstract Real-time imaging of transient structure of the electronic excited state is fundamentally critical to understand and control ultrafast physics and chemistry. However, the coherent nuclear motion in a specific excited state is yet to be captured accurately. Here, snapshots of the vibrational wave-packets of the excited (A) and ground states (X) of D$\rm_{2}$O$^{+}$ were acquired simultaneously with sub-10 picometer and few-femtosecond spatiotemporal precision, using a novel approach based on electron recollision-assisted Coulomb explosion. We visualised large amplitude bending and stretching motions for the A state, which significantly increased $\rm \theta _{DOD}$ and R$\rm_{OD}$ by approximately 50$^\circ$ and 10 pm, respectively, within 8 fs after initial tunneling ionization. In contrast, for the X state, only the prominant stretching motion is initialised with a bond extension of 7 pm within 5 fs. Another higher excited state with an asymmetric folding structure is experimentally established, which can be efficiently populated via the excitation of electron recollision. We demonstrate the remarkable dynamical vibrational fingerprints of these excite states and pave the way towards to make a movie of excited state-resolved ultrafast molecular dynamics and light-induced chemical reaction.