Theoretical investigation of the potential energy surface of the Si ₂NP molecule

The structures, energetics, spectroscopies, and stabilities of the singlet and triplet Si₂NP isomeric species are explored at the DFT/B3LYP, QCISD, and CCSD(T) (single-point) levels. A total of 23 minimum isomers and 32 interconversion transition states are located. Generally, the triplet species lie energetically higher than the singlet ones. At the CCSD(T)/6-311+G(2df)// QCISD/6-311G(d) level, there are two nearly isoenergetic singlet isomers as global minima, i.e., a linear SiNSiP¹1 (0.0) and a puckered cSiNSiP¹4 with P-N cross-bonding (-0.6). The third low-lying isomer is a planar four-membered ring cSiNSiP¹5 (3.3) with Si-Si cross-bonding. All the three isomers have reasonable kinetic stabilities and might be observable either in laboratory or in space. Moreover, the structural and bonding analyses indicate that¹1 possesses typical Si≡P triple bonding. Since up to now, stable Si≡P triply bonded species are still experimentally unknown, isomer¹1 may represent such a good example. Finally, the similarities and discrepancies of Si₂NP are compared to the other analogous 18-valence electrons species AA′BB′ (A, A′ are group IV elements and B, B′ are group V elements) such as C₂N₂ and Si₂P₂. The present study is the first one to consider such series with three higher-row atoms.