We constructed the PES starting from the Franck-Condon (FC) region to minimum energy crossing points (MECP) to understand the non-radiative decay of Pa. We found two MECPs (MECP1 and MECP2) having lower in energy than FC. In MECP1, -CHO group became nonplanar along with elongation of CO bond. In MECP2, excited-state intramolecular proton transfer (ESIPT) from NH to CO occurs. In both the MECPs, we noticed that π-π * state got involved in conical intersection with S 0 . A flat PES, reminiscent of the natural pyrimidine bases, was obtained along MECP1. On the other hand, MECP2 shows a high barrier with respect to the minima, but perhaps, more importantly, it is a pathway that is blocked in the biological system.