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 XΣ 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(C) = 115(6) MHz, A(C) = 65(15) MHz, A(H) = 34(6) MHz, A(H) = 5(10) MHz, A(D) = 5(3) MHz, A(Mg) = 82(5) MHz, and A(Mg) = 85(10). Comparisons are made between the electronic structure of this radical and the MgCH 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 XΣ ground electronic state was shown to be 1σ2σ3σ1π4σ5σ6σ7σ2π2π 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) 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.