Relative stabilities of (NO)2 Original Research Article

Geometrical structures for the (NO)2 are calculated using ab initio Hartree–Fock (SCF), second-order Møller–Plesset perturbation, and coupled cluster with the single, double, and triple substitution methods with a triple zeta plus polarization basis set including diffuse Rydberg basis functions. The structure of (NO)2 can be described by two interactions (N⋯N, N⋯O). One is the ONNO structure with an (N⋯N) interaction. In this structure, acyclic cis-ONNO with C2v-symmetry, acyclic trans-ONNO with C2h, and cyclic ONNO with trapezoidal structure (C2v) are optimized at the MP2 level. The other structure is the ONON structure with an (N⋯O) interaction. In the structure, acyclic cis-ONON with Cs-symmetry and cyclic ONON of the rectangular (C2h), square (D2h), rhombic (D2h), and parallelogramic (D2h) geometries are also optimized. It is found that acyclic cis-ONNO (1A1) is the most stable structure. The binding energies and the relative energy gaps among the isomers are found to be relatively small.