Deformation, nuclear motion and fragmentation of core-excited CO ₂ probed by multiple-ion coincidence momentum imaging

The nuclear motion and geometry in core-excited CO₂ are probed using a multiple-ion-coincidence imaging technique. We demonstrate that CO ₂ has a linear stable geometry in the C/O 1s^-1 core-ionized state and a bent geometry in the C/O 1s^-1π* core-excited state. The molecules in the C/O 1s^-1π* A ₁ and B₁ Renner-Teller states are probed to be bent in the A₁ state and linear in the B₁ state. The O-O correlation angle distributions are well reproduced using a Coulomb explosion model which takes account of the zero point bending motion in the ground state, the classical bending motion along the potential energy curve of the core-excited state within the core-hole lifetime and the initial inhomogeneous charge distribution in the multiply charged molecular ion just before the dissociation. When the photon energy is tuned to be higher (lower) energy than the 1s ^-1 π* resonance center, the events for the 1s^-1 π* A₁ states that result in the low O-O correlation angle distribution are suppressed (enhanced).