Millimeter and submillimeter rest frequencies for the MgF radical

The pure rotational spectrum of the MgF radical in its ground X ²Σ⁺+ electronic state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Rotational transitions arising from the υ = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, ²⁴MgF, have been recorded, as well as those arising from the υ = 0 state of the ²⁵Mg and ²⁶Mg isotopomers. Rotational and fine-structure constants have been determined for these molecules, as well as hyperfine parameters for both the ¹⁹F (I = 1/2) and ²⁵Mg (I = 5/2) nuclei. The rest frequencies presented here for MgF have an estimated accuracy of ±200 kHz, and will enable astronomical searches to be carried out for this fluoride radical. Magnesium fluoride may be present in the late-type carbon star IRC + 10216, where AlF appears to be abundant.