The structures, energetics, spectroscopies, and isomerization of the doublet Si 2 PO radical are explored at various levels. At the UB3LYP/6-311+G(2df) level, a total of 12 minimum isomers and 15 interconversion transition states are located. Four cyclic isomers are found to be thermodynamically and kinetically stable at the higher UCCSD(T)/6-311++G(2df)//UM062x/6-311+G(2df)+ZPVE and may be experimentally or astrophysically observable. The lowest-lying isomer 1 c-SiOSiP ( 2 B 2 ) (0.0 kcal/mol) corresponds to a rhomboidal-type structure similar to the global state of Si 2 NO, followed by another three-membered ring isomer 3 O-cSiSiP ( 2 A 0 ) (23.1 kcal/mol) which is similar to the global state of [Si, C, P, O]. Another two stable isomers are the three-membered ring isomers 11 P-cSiSiO (35.0 kcal/mol) and 6 O-cPSiSi (47.5 kcal/ mol), respectively. The bonding nature of the four isomers is analyzed. Meanwhile, the calculated results are compared with its analogs SiCPO, Si 2 NO, and Si 2 PS. Implications in the laboratory and interstellar space are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of Si 2 PO in the laboratory and space.