Probe of bending motion following the 1s(-1)pi* excitation of N2O.
The doubly degenerate core-excited Pi state of N2O splits into two due to the static Renner-Teller effect. The lower state, A1, has a bent stable geometry and the molecule excited to this state starts to deform itself toward this bent geometry. To probe the effect of the potential energy surfaces of the core-excited A1 states on the nuclear motion, we measure the momenta of the three atomic ions in coincidence by means of the ion momentum imaging technique. We find that the potential energy surface affects the molecular deformation significantly. N2O in the terminal N 1s(-1)3piA1 excited state is observed to be bent more than that in the central N 1s(-1)3piA1 excited state. This means that N2O in the terminal N 1s(-1)3piA1 excited state bends faster than that in the central N 1s(-1)3piA1 excited state. When the excitation energy is decreased within the 1s(-1)3pi resonances, the nuclear motion in the A1 states becomes faster. This is interpreted by the notion that the excitation occurs onto the steeper slope part of the potential energy surface of the excited state for the lower excitation energy. The branching ratio of the A1 excitation increases with the decrease in the excitation energy.
Deformation, nuclear motion and fragmentation of core-excited CO2 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 CO2 has a linear stable geometry in the C/O 1s −1 core-ionized state and a bent geometry in the C/O 1s −1 * core-excited state. The molecules in the C/O 1s −1 *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 * resonance center, the events for the 1s −1 *A 1 states that result in the low O O correlation angle distribution are suppressed (enhanced).
The effect of the nuclear motion on the electronic decay of core hole excited states in molecules
We have measured the vibrational fine structure in the electronic decay spectrum of the N 1s→1πg core electron excited state in molecular nitrogen. The Franck–Condon analysis of the vibrational substructure shows that within the 10−14 s lifetime of the core hole excited state the molecule adjusts to the excited state configuration, characterized by a change in bond length by 0.071 A. Interference effects due to the short lifetime of the intermediate state play only a minor role.