One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays

Sebastian Eckert, Vinícius Vaz da Cruz, Faris Gel'mukhanov, Emelie Ertan, Nina Ignatova, Sergey Polyutov, Rafael C. Couto, Mattis Fondell, Marcus Dantz, Brian Kennedy, Thorsten Schmitt, Annette Pietzsch (+2 others)
2018 Physical Review A  
The concept of the potential energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate ro-vibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the
more » ... ters of gravity of groups of close lying vibrational levels. We show here that resonant inelastic X-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center-of-gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective 1D Hamiltonian along the propagation coordinate of the core-excited wave packet. This novel concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground state PES along three complementary directions for the showcase H2O molecule.
doi:10.1103/physreva.97.053410 fatcat:jlhsudc4draapobhvx3invexaa