Figure 1: (a) A schematic one-dimensional curve of two coupled adiabatic PESs, (b) an example of for the PESs in (a), and (c) comparisons between stationary points on (with  kJ/mol) and those on the S1-PES of H2CO (see Section 2.4 for the ab initio calculation level). Each structure shown in (c) corresponds to S1-MIN, S1-TS, and S0/S1-MSX (conical intersection), respectively, and stationary structures on are overlapped in black behind them. At S1-MIN and S1-TS, the stationary structures on are identical to them within the convergence criteria (see text) of geometry optimization and cannot be seen. -MIN can barely be seen behind S0/S1-MSX.