A matrix isolation ESR investigation of Mg⁺-N₂

The adducts formed between ²⁵Mg⁺ with ¹⁴N₂ and ²⁵Mg⁺ with ¹⁵N₂ have been trapped in a solid neon matrix and studied with electron spin resonance (ESR) spectroscopy. These radical species were formed through the interaction of laser ablated magnesium and nitrogen gas. The Mg⁺-N₂ radical species was found to have a ground electronic state of ²Σ⁺ in a linear configuration with discrete coupling to the proximate nitrogen resolved in the spectra. Fitting the ESR spectra allowed magnetic parameters to be determined as follows: g_⊥ = 2.0012(5), g_∥ = 2.0015(8), A_⊥(1-¹⁴N) = 32(3) MHz, A_∥(1-¹⁴N) = 34(5) MHz, A_⊥(1-¹⁵N) = 45(4) MHz, A_∥(1-¹⁵N) = 47(6) MHz, A_⊥(²⁵Mg) = -581(5) MHz, and A_∥(²⁵Mg) = -582(5) MHz, and estimates derived for A_⊥(2-¹⁴N) = 1(2) MHz, A_∥(2-¹⁴N) = 2(5) MHz, A_⊥(2-¹⁵N) = 2(2) MHz, and A_∥(2-¹⁵N) = 4(6) MHz. Ab initio calculations using the coupled-cluster single double triple methodology showed that the linear form was 59.7 kcal mol^-1 more stable than the T-shaped form. The potential energy curve around the equilibrium geometry was explored using the complete active space self-consistent field approach, and Hartree-Fock singles and double configuration interaction and multireference singles and double configuration interaction calculations of the hyperfine coupling constants were undertaken, and reasonable agreement with the experiment was observed.