A matrix isolation ESR investigation of the MgCH radical

The MgCH radical and its magnesium-25, carbon-13, and deuterated isotopologs have been isolated in low temperature neon matrices and examined by the matrix isolation electron spin resonance technique for the first time. The radicals were formed through the reactions of laser ablated natural abundance magnesium metal and magnesium-25 enriched magnesium metal with carbon-13 and deuterated isotopologs of acetone. The MgCH radical was shown to have a X⁴Σ^- ground electronic state, and the magnetic parameters determined for this state were g_⊥ = 2.001 81(45), g_∥ = 2.0018(10), D = 4970(5) MHz, A_⊥(¹³C) = 115(6) MHz, A_∥(¹³C) = 65(15) MHz, A_⊥(H) = 34(6) MHz, A_∥(H) = 5(10) MHz, A_⊥(D) = 5(3) MHz, A_⊥(²⁵Mg) = 82(5) MHz, and A_∥(²⁵Mg) = 85(10). Comparisons are made between the electronic structure of this radical and the MgCH₃ and MgN radicals. Theoretical hyperfine parameters were also evaluated for the MgCH radical, and a potential energy surface for the low-lying electronic states was constructed using complete active space multiconfigurational self-consistent field theory. The leading configuration (96.6%) for the X⁴Σ^- ground electronic state was shown to be 1σ²2σ²3σ²1π⁴4σ²5σ²6σ²7σ¹2π¹2π¹ with an Mg-C bond length of 2.041 Å for a fixed C-H bond length of 1.090 Å. The Mg-C bond dissociation energy (D_e) was 48.26 kcal/mol. The optimized geometry from a density functional theory calculation using the B3LYP functional gave a Mg-C bond length of 2.061 Å and a C-H bond length of 1.090 Å.