A matrix isolation ESR investigation of Mg ⁺ -N ₂

The adducts formed between ²⁵ Mg ⁺ with ¹⁴ N ₂ and ²⁵ Mg ⁺ with ¹⁵ N ₂ 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 ⁺ -N ₂ radical species was found to have a ground electronic state of ² ς ⁺ 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- ¹⁴ N) = 32(3) MHz, A _⊥ (1- ¹⁴ N) = 34(5) MHz, A _∥ (1- ¹⁵ N) = 45(4) MHz, A _⊥ (1- ¹⁵ N) = 47(6) MHz, A _∥ ( ²⁵ Mg) = -581(5) MHz, and A _⊥ ( ²⁵ Mg) = -582(5) MHz, and estimates derived for A _∥ (2- ¹⁴ N) = 1(2) MHz, A _⊥ (2- ¹⁴ N) = 2(5) MHz, A _∥ (2- ¹⁵ N) = 2(2) MHz, and A _⊥ (2- ¹⁵ N) = 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.