Fig. 6. Geometric dependence of valence to oxygen K-edge transitions. (a) Valence and core-excited state potential energy surfaces along H-transfer (left) and torsion (right) coordinates as obtained at the XMS-CASPT2/cc-pVDZ level. Core-excited state potential energies have been shifted by −4.254 eV. Note the different scaling of the x-axes of the left and right sides of the FC point. Colored arrows highlight the trends in valence-core excitation energy shifts for the most sensitive transitions (red: red-shifting and blue: blue-shifting in the direction of the arrow). (b) Mulliken charges of the ground state along the same coordinates. Horizontal dashed lines indicate the corresponding charge at the origin. To avoid ambiguity due to arbitrary wavefunction mixing at geometry (v), the charges were computed by linear interpolation between the previous point on the path and an extrapolated point obtained by displacing along the projection of the previous displacement vector onto the branching plane.