ESR spectra of the MnO, MnO2, MnO3, and MnO4 molecules at 4 °K

Abstract

The molecules MnO, MnO₂, MnO₃, and MnO₄ have been prepared by the vaporization and reaction of manganese atoms with O₂, N₂O, or O₃ and isolated in various inert‐gas matrices at 4 °K. ESR has been used to determine magnetic parameters which are interpreted in terms of molecular geometry and electronic structure. MnO is confirmed to have a σπ²δ², ⁶Σ⁺ ground state with g_⊥=1.990(7) (assuming g_∥=g_e) and a zero‐field splitting in accord with the gas phase value ‖D‖=1.32 cm⁻¹. Hyperfine splittings due to the ⁵⁵Mn (I=5/2) nucleus are ‖A_∥‖=176(8) and ‖A_⊥‖=440(11) MHz. MnO₂ is a linear ⁴Σ⁻ molecule with probable configuration σδ², ‖D‖=1.13 cm⁻¹ (assuming g_∥=g_⊥=2.0023), ‖A_∥‖=353(11), ‖A_⊥‖=731(11) MHz. MnO₃ exhibits very large hf splittings ‖A_∥‖=1772(3) and ‖A_⊥‖=1532(3) MHz indicative of a sd_z2 hybrid ²A₁ ground state of D_3h symmetry. The spectrum of MnO₄ is consistent with a C_3v molecule distorted from a ²T₁ electronic state in tetrahedral symmetry by a static Jahn–Teller effect. g and A tensors are slightly anisotropic: g_∥=2.0108(8), g_⊥=2.0097(8), ‖A_∥‖=252(3), ‖A_⊥‖=196(3) MHz. The electron hole is almost entirely in an oxygen π‐bonded orbital with one oxygen atom displaced along its Mn–O bond axis.