Millimeter-wave spectroscopy of MgF: Structure and bonding in alkaline-earth monofluoride radicals

The pure rotational spectrum of the MgF radical in its ground electronic state (X²∑⁺) has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from the v = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, ²⁴MgF, have been observed. In addition, spectra of the isotopomers ²⁶MgF and ²⁵MgF in the natural abundances of magnesium have been detected. Rotational and fine structure constants have been determined for these species, as well as hyperfine parameters for the fluorine nucleus (I = 1/2). For ²⁵MgF, the hyperfine structure was also resolved arising from the magnesium nucleus, which has I=5/2, yielding the ²⁵Mg hyperfine and quadrupole constants. Comparison of these hyperfine parameters with those of the heavier alkaline-earth monofluorides and the free ²⁵Mg⁺ atom suggests that there is an increase in covalent bonding in MgF vs its heavier fluoride counterparts. This behavior is also apparent in the hybridization of the wave function of the unpaired electron in MgF, which appears to consist of almost equal s and p character.