ESR spectrum and structure of the MgOH radical

The MgOH molecule has been trapped in solid argon and neon at 4 °K, and its ESR spectrum measured. It has been isolated in these matrices by (1) code positing Mg atoms with a matrix gas containing 1% H2O2, (2) codepositing Mg atoms with a matrix gas and the products of a microwave discharge of H2O vapor, or (3) passing the metal atoms, along with H2O vapor, through a tantalum cell at 1700 °C before quenching in the matrix gas. g tensors and nuclear hyperfine components for interaction with 25Mg and H were determined. In both argon and neon these magnetic tensors appear to have axial symmetry, indicating that the molecule is probably linear (2Σ ground state). In neon g‖= 2.0017(1), g⊥= 2.0007(1), |A‖ (25Mg)|= 312.7(3) MHz, |A⊥ (25Mg)|= 300.7(3) MHz, |A‖(H)|= 14.8(3) MHz, |A⊥(H)|= 10.1(3) MHz. Spin density distribution derived from hyperfine splittings places a majority of the spin on Mg and implies that the molecule is highly ionic. A CNDO calculation slightly favors a linear structure and supports the observed spin distribution. Trapped Mg+ and probably MgO2H were also observed in the ESR spectra. The large excess of Mg atoms in the matrices dominated the optical absorption spectrum in the ultraviolet.