Electron spin resonance and theoretical studies of the 14N⋅⋅⋅⋅14N and 15N⋅⋅⋅⋅15N spin-pair radicals in neon matrices: The effects of mixing among the 1Σg+, 3Σu+, 5Σg+, and 7Σu+ electronic states

Abstract

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 1Σg+, 3Σu+, 5Σg+, and 7Σu+ 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.

Matrix Isolation ESR and Theoretical Study of ZnN

“…Small interactions between the host and the trapped species can result in small changes in the spectroscopic properties observed, in this case, the D -value, and as the matrix is believed to be crystalline, these interactions are specific to a particular site . The absorption near 1730 G corresponds to two spin-coupled N atoms, N···N, which has been described by Knight et al The position of the three peaks is consistent with the spectrum generated by a 4 ∑ – radical with | D | between 5000 and 10 000 MHz. A quartet radical with this | D | value produces a set of perpendicular ( xy 1 ) lines around 1900 G, a set of off-angle lines around 5000 G and another set of perpendicular ( xy 3 ) lines around 6000 G, which are all shown in Figure .…”

Electronic, Structural, and Hyperfine Interaction Investigations on Rydberg Molecules: NH4, OH3, and FH2

“…Each neon atom is surrounded by 12 neon atoms. The distance between two neon atoms is 3.16 Å . In our calculations, only one shell was employed and the center neon atom was replaced with NH 4 and OH 3 molecules.…”

“…ESR assesses the interaction of the intrinsic electronic spin with the magnetic nuclei. In recent years, there has been a number of ESR investigations (both theoretical and experimental) for gaining knowledge about electronic structures, spin density distributions, and hyperfine splittings for various radical/ion systems. − In this paper, we reexamine the electronic structures of NH 4 , OH 3 , and FH 2 at the MP2 level with a large basis set augmented with Rydberg-type diffuse orbitals. The potential energy surfaces are calculated, and the relative stabilities of NH 4 , OH 3 , FH 2 , and their isotopic counterparts are discussed.…”

Analysis of wave functions for open-shell molecules

“…In a pair of papers, Knight et al, have demonstrated how eqn (2.1) with the Heisenberg interaction term can be used to fit the ESR spectrum of matrix separated H atoms in 2 S states and for matrix separated N atoms in 4 S states. 3,4 As both experiments involved atoms with zero orbital angular momentum (S states), additional complexity from rotational degeneracy was avoided and the separate radical D KK values were zero. The separation distances were large enough however that the D KL values (which decrease like the inverse cube of the separation distance) were larger than J (which decreases exponentially).…”