Fig. 6. Structures of the water trimer obtained from CASPT2(4,8) calculations in the S0 and S1 states; G3-[2] and G3-[1] = global and local minimum energy geometries in the S0 state, respectively; E3-[1]‡ = transition structure in the S1 state; E3-[2] = equilibrium structure in the S1 state; E3-[3] and E3-[4] = O–H dissociated structures in the S1 state. ΔE = Relative energies with respect to the total energy of structure G3-[1]; μ= dipole moment. The value of the HOMO and LUMO isosurfaces is 0.065.
