Electron spin resonance and theoretical studies of the ~(14)N....~(14)N and ~(15)N....~(15)N spin-pair radicals in neon matrices: The effects of mixing among the ~1#SIGMA#_g~+, ~3#SIGMA#_u~+, ~5#SIGMA#_g~+, and ~7#SIGMA#_u~+ electronic states

摘要

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 ~1#SIGMA#_g~+, ~3#SIGMA#_u~+, ~5#SIGMA#_g~+, and ~7#SIGMA#_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 ~(15)N....~(15)N radical in the dominant trapping site had magnetic parameters of g = 2.0016(2), A(~(15)N) = 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 A. 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.