MuCO: Elusive isotopomer of HCO

Abstract

Calculations are presented of the structure, stability and certain molecular properties of the formyl radical, HCO, and its muonium-substituted counterpart, MuCO. Møller-Plesset perturbation theory and quadratic configuration interaction calculations arrive at similar results, whereas those using density functional theory appear less reliable. Special attention is paid to the effects of zero-point energy, with the remarkable conclusion that whereas the reaction × + CO → XCO is exothermic for × = H, it must be endothermic for × = Mu. The isomer COMu is less stable still and both MuCO and COMu are close to dissociation. These findings help explain the fast muon spin relaxation observed in MuCO and, together with the unusually high spin density on the muon, the difficulty in detecting a muon spin rotation spectrum.