Theoretical study on the potential energy surface of the Si2PO system

The structures, energetics, spectroscopies, and isomerization of the doublet Si2PO 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 (2B2) (0.0 kcal/mol) corresponds to a rhomboidal-type structure similar to the global state of Si2NO, followed by another three-membered ring isomer 3 O-cSiSiP (2A′) (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, Si2NO, and Si2PS. 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 Si2PO in the laboratory and space.