SiC₂P: A promising molecule with two stable cyclic isomers

The structures and isomerization of SiC₂P species are explored at various levels. Thirteen minima are located connected by 19 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest energy isomer is a linear form SiCCP 1 whose structure mainly resonates between |Si=C=C=P|· and |Si=C·-C≡P| with the former bearing somewhat more weight. The second and third low-lying isomers are cyclic cSiCCP 5 (with Si-C cross-bonding) at just 3.2 kcal/mol and cSiCPC 7 (with C-C cross-bonding) at 10.4 kcal/mol, respectively. All the three isomers 1, 5, and 7 possess considerable kinetic stability either toward isomerization or dissociation, and thus are expected to be observable. The calculated results are compared to those of the analogous molecules C₃N, SiC₂N, and C₃P. Implications in the interstellar and P-doped SiC vaporization processes are discussed.