We computed relevant stationary points on the lowest triplet state PES with CCSD/6-31G* and CCSD/cc-pVTZ. For acetylene-and propyne-derived species, the MECPs were computed with EOM-EE-CCSD/6-31G*. For ethylene and propene, the MECPs were computed by EOM-DIP-CCSD/6-31G*. We used such a small basis set to avoid problems due to unstable dianionic reference. The calculations of MECPs are described in Section 3.1 below. All electronic structure calculations were carried out using the Q-Chem package.