Fig. 3: Illustration of the TBD mechanisms of H2O upon VUV excitation.
Photoexcitation populates the nd Rydberg state (nd RS) which undergo efficient non-adiabatic coupling to the \(\widetilde{D}\) state. The light blue arrow displays the photoexcitation process and the gray oval represents the crossing region between the nd RS and the \(\widetilde{D}\) state. Path 1 illustrates the possible direct dissociation route from the \(\widetilde{D}\) state to form O(1D) + 2H products (the yellow curve). Paths 2 and 3 illustrate plausible routes for the more complicated O(3P) + 2H dissociation paths: from the \(\widetilde{D}\) state to the \(\widetilde{B}\) state and then to the ground state via the two conical intersections (CI #1 or CI #2), following the initial internal conversion from the excited nd RS to the \(\widetilde{D}\) state (the red curves). This picture is consistent with the observed angular anisotropy for the two channels: the O(1D) + 2H channel is a more direct dissociation process with larger angular anisotropy, while the O(3P) + 2H channel is a more complicated dissociation process with smaller angular anisotropy. The PES contour color from blue to red represents the potential energy from 0 to 12 eV.
