The missing halide: Millimeter-wave spectroscopy of the MgI radical (X2Σ+)

The pure rotational spectrum of the MgI radical in its ground electronic state (X-2 Sigma(+))has been measured using millimeter/submillimeter wave direct absorption techniques in the region of 200-300 GHz. The molecule was created in a DC discharge by the reaction of magnesium vapor, produced in a Broidatype oven, with CH3I. Between five to twelve transitions were recorded for the v = 0, 1, and 2 vibrational states of (24)Mgl, as well as the v = 0 state for the isotopologues (MgI)-Mg-25 and (MgI)-Mg-26, measured in their natural magnesium abundance. All observed transitions exhibited large spin-rotation splittings. Rotational, centrifugal distortion, and spin-rotation constants were determined for each isotopologue and the excited vibrational states of (24)Mgl. Equilibrium parameters B-e, alpha(e), D-e, beta(e), gamma(e) and gamma(e) were derived for the main isotopologue, as well as the equilibrium bond length, r(e) = 2.5730 (1) angstrom. The large spin-rotation constant of gamma similar to 300 MHz in MgI is thought to arise from second-order spin-orbit coupling originating in the nearby A(2)Pi state, with possible contributions from other excited (2)Pi states. (C) 2017 Elsevier Inc. All rights reserved.