Electron spin resonance and theoretical studies of the \u3csup\u3e14\u3c/sup\u3e N\u3csup\u3e....14\u3c/sup\u3eN and \u3csup\u3e15\u3c/sup\u3eN\u3csup\u3e....15\u3c/sup\u3eN spin-pair radicals in neon matrices: The effects of mixing among the \u3cem\u3e\u3csup\u3e1\u3c/sup\u3eΣ+g, \u3csup\u3e3\u3c/sup\u3eΣ+u, \u3csup\u3e5\u3c/sup\u3eΣ+g,\u3c/em\u3e and \u3cem\u3e\u3csup\u3e7\u3c/sup\u3eΣ+u\u3c/em\u3e electronic states

The first experimental and theoretical study of the N⋅⋅⋅⋅N spin-pair radical is reported. Its high-resolution ESR (electron spin resonance) spectrum has been observed in neon matrices and interpreted on the basis of weakly interacting atoms using a model recently developed for the H⋅⋅⋅⋅H spin-pair. To fully interpret the N⋅⋅⋅⋅N radical results it was necessary to include electronic state mixing effects among all possible spin states, namely the 1Σ+g, 3Σ+u, 5Σ+g, and 7Σ+u states. Several different trapping sites were observed which indicated the interaction of N atoms at distinctly different separation distances in the neon lattice. Calculated J values at the complete active space self-consistent field (CASSCF) level (TZP basis set) were compared with the experimental results for the various trapping site distances. The 15N⋅⋅⋅⋅15N radical in the dominant trapping site had magnetic parameters of g=2.0016(2), A(15N)=15.9(1) MHz, D=−178(1)MHz and J=468(2) MHz. Using the point dipole approximation this corresponds to a N⋅⋅⋅⋅N separation distance of 6.41 Å. A most unusual type of magnetic dipole transition was observed that involves a transition between electronic states of formally different S values where S is the total spin quantum number for a given electronic state